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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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SESSION E.
NEW FACILITY DESIGN CONSIDERATIONS

CHAIR

Leonard Van Houten

SPEAKERS

E.J.Schmeltz, P.E.

Jens Korsgaard

C.Lincoln Crane

Richard Harley

Glen Pickering

Douglas L.Inman*

Scott A.Jenkins

*  

Presentation not made during the Symposium

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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PLANNING CONSIDERATIONS FOR PORTS IN COHESIVE SEDIMENTS

E.J.Schmeltz, P.E.

PRC Engineering, Inc.

Ports located in an estuarine environment dominated by fine-grained or cohesive sediments present problems in port planning that differ in some respects from locations characterized by more coarse-grained material and rock. In general these locales are characterized by shallow water, shifting shoals, and a significant freshwater input.

The basic difficulty associated with the installation of port facilities in this type of an environment is that dredging requirements can be very high. This is true both of initial construction and subsequent maintenance. Essentially, sediment deposition results from modifications in the flow regime induced by construction of the port facilities. An awareness of the basic impacts on deposition patterns caused by manmade changes such as channel dredging and installation of port structures is necessary in order to minimize future maintenance while maximizing the safety and operational efficiency of the port.

The purpose of this paper is to briefly discuss some of the factors that require attention in the planning of port facilities in this type of location and to provide examples highlighting these considerations.

SITE LOCATIONS

Ideally, a port location is characterized by protection from wave action, naturally deep water, favorable bottom conditions, access to existing infrastructure, and upland areas that are adequate for the development of shoreside facilities. The site of a port is, however, often dictated by factors other than engineering criteria, such as proximity to existing markets, and diverse economic and political factors. The lack of availability of natural harbors in a specific region may dictate that a selection be made between the lesser of several evils.

Port facilities require straight, deep navigation channels with dimensions adequate for safe passage of the largest anticipated vessels. Turns in channels need to be a large enough radius to minimize assistance in navigation. Turning circles adjacent to piers and wharves are necessary, and anchorage areas are generally desirable if not always mandatory. Structures such as piers, wharves, bulkheads and moorings should be easy to construct given the site conditions.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 1 San Francisco, California.

FIGURE 2 Kings Bay, Georgia.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Dredging requirements, both in terms of initial construction and maintenance, should be minimal. Many of the world’s finest harbors are located at sites that have many of the above attributes, including San Francisco, New York, and Rio de Janiero to name but a few. Part of the port of San Francisco is shown in Figure 1.

Existing conditions in estuaries are often dramatically different from the ideal case. Extensive areas of naturally shallow winding water courses are more characteristic of these areas than straight deep channels. In much of the developed world, the more desirable port sites are already utilized so that many of the alternatives tend to be less than perfect. An example of a less than ideal port site is Kings Bay Georgia Figure 2.

In evaluating a port location, it is generally desirable to minimize disruption of the estuarine system induced by man-made improvements. Changes introduced for the port can have a significant impact on circulation patterns, saline intrusion, and sedimentation patterns and rates. The less the magnitude of the required changes in the natural system, the less will be the adverse impacts on port operations.

The impacts on sedimentation rates and patterns are most noticeable where sediments are composed of clays and other lightweight material affected by relatively weak currents. Figure 3 shows annual shoaling rates as a function of channel depth for Savannah Harbor. Clearly the result of increasing channel depth is a marked increase in sedimentation rates in the channel.

Ultimately a balance must be achieved between initial dredging, future maintenance, port operations, and adverse environmental impacts. For example, available evidence indicates that the majority of U.S. estuaries were in a state of dynamic equilibrium prior to disruption of the entrance bars and shoal areas for navigation purposes (Ippen, 1966). In the majority of these ports, significant maintenance dredging is currently necessary to maintain navigable depths.

The following sections discuss planning factors associated with more specific port improvements.

CHANNEL GEOMETRY/DREDGING

Because of the potential magnitude and extent of its impact on the flow regime in an estuary, dredging is a major factor in the changes in sedimentation rates due to port development. Increases in sedimentation are primarily associated with changes in flow velocity and direction and saline intrusion induced by the introduction of navigation channels, turning basins, and berth facilities.

In planning for port facilities the depth and size of navigation channels are controlled by a combination of environmental factors affecting vessel navigation as well as the maximum size of the vessel expected to utilize the port facilities. Detailed discussions are provided by Bruun (1981) and Quinn (1982) among others. Depth of the channel is generally controlled by tides, maximum vessel draft,

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 3 Shoaling rates as a function of channel depth (Savannah Harbor).

underkeel clearance requirements, ship motions, vessel squat, and anticipated shoaling.

In an estuarine environment vessel draft, underkeel clearance and anticipated shoaling can be affected by flow characteristics and bottom conditions. If a significant freshwater inflow exists in the vicinity of port facilities, vessel draft can change as a result of changes in water density. If this condition is anticipated, an increase in vessel draft beyond that realized in salt water must be accommodated.

In ports with hard bottoms, an underkeel clearance of 10 percent of the vessel draft plus anticipated motion is normally desirable in order to preclude damage to the ship from contact with the bottom. In this regard, one of the redeeming values of ports located where bottom conditions are characterized by silts and clays presents itself—soft bottom. As a consequence, a reduction in underkeel clearance requirements and dredging tolerances is acceptable. With a soft bottom, underkeel clearance can be reduced to about 4 ft; dredging tolerances can be decreased.

Channel side slopes are generally flatter in fine-grained sediments than in granular materials, increasing initial dredging quantities. Flow velocities are also reduced further due to the increase incross-sectional area. Increases in the channel cross section and changes in alignment generally reduce current velocities in the area resulting in increased deposition and commensurate increases in maintenance dredging.

One of the less obvious difficulties encountered in establishing dredged depths/quantities where fine-grained sediments are encountered lies in defining “bottom.” With hard bottoms the process is relatively straightforward, and simple fathometer or lead line survey will suffice.

Where fine-grained sediments predominate, a fluid-mud suspension may exist on the bottom, which complicates definition of a navigable

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

depth. Lead lines yield the depth to a reasonably solid bottom while depth recorders do not clearly define the water-mud interface.

An assessment of this problem has been undertaken by the Permanent International Association of Navigation Congress. This group defines a nautical depth considered safe to accept as the bed of the channel which precludes damage to vessels and that does not adversely affect maneuverability. At the port of Rotterdam, the group recommends that the “bottom” be defined where the specific gravity of the layer is 1.2. The working group further recommends, however, that the particular value for individual sites be based on local conditions and requirements. The condition also has been noted at the entrances to the Suez Canal at Port Said. In Rotterdam, the thickness of the layer was reportedly 2.5 m. The relationship between depth and density in the fluid mud layer is shown in Figure 4.

SALINE INTRUSION

While making navigation practical, changes in the hydraulic characteristics of an estuary induced by dredging also increase saline intrusion in the waterway. A saline bottom wedge overlain by fresh water discharging to the sea exists in various forms in all estuarine situations. Flocculation at the interface results in the deposition of material on the bottom. Whether the saline intrusion is highly stratified, partly mixed, or well mixed, the introduction of navigation channels, turning basins, etc. will modify the type and extent of the wedge.

Changes in saline intrusion result in, at a minimum, changes in the deposition patterns in the port area and often affect the rate of accumulation as well. Returning to the earlier example of Savannah Harbor, Figure 3 shows the changes in maintenance dredging requirements as a function of depth for an upstream (7.4 mi) and downstream (5.1 mi) reach. Note that increases in channel depth tend in this case to increase relative shoaling in the upstream areas, while decreasing deposition in the lower portions of the harbor on a relative basis.

DREDGED MATERIAL DISPOSAL

Disposal of both initial dredged material and subsequent maintenance dredging may also prove difficult for fine-grained sediments. For ports in areas with granular materials, the dredged spoil can be utilized as fill in upland areas. However, with fine-grained sediments, dredged material cannot generally be used immediately as fill, if at all. Rather, dewatering is required and a considerable amount of time may be necessary prior to utilization on a site.

If not structurally adequate for port facilities, dredged material can be disposed at sea, deposited in holding areas on land, or perhaps

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 4 Bed density survey, Immingham dock entrance, 1975.

used as capping material for landfills. In more developed ports, there is the risk of encountering contaminated materials requiring special treatment and handling. Some portions of lower New York Bay are characterized by this type of problem to greater or lesser extents.

Finally, dredging of fine-grained sediments results in significant turbidity and can pose an environmental threat to downstream areas. As a consequence it is often necessary to control this problem with sediment screens and special controls at spoil areas.

ORIENTATION AND ALIGNMENT

Proper orientation and alignment of channel improvements and port structures can minimize the amount of maintenance dredging required for the safe operation of a port. Large-scale dredging in order to realign and deepen approach channels or to provide turning basins generally results in increased sedimentation. In addition, the deepening and improvements in the hydraulic characteristics of the channel will result in an increase in salinity intrusion and the deposition of material within the harbor as noted above.

In general, orientation of both channels and berth will be best if they are arranged parallel to the flow of the natural channels. This arrangement tends to minimize disruption of the flow regime and keep sediment moving to the maximum extent possible past the port facilities. Of course, increases in channel depth and/or dimension tends to reduce flow velocities and increase the resultant settling of fine materials.

From the perspective of port operations, large-radius turns are desirable, but the introduction of these types of channels may result in a tendency for the channel to meander. A balance must therefore be achieved between the operational needs of the vessels and the stability of the facility.

Care must also be exercised in the placement of structures along the banks of the waterways in the estuary. Facilities located to the outside bank of a curve will have a tendency toward erosion; those

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

placed on the inside of the curve will have a tendency toward deposition.

In addition to the problem of limiting maintenance dredging at the facilities, caution must be exercised in terms of the effect of dredging on other areas downstream of the facility. The dredging conducted will not only disrupt the dynamic equilibrium of the immediate area, but can result in a sediment trap. Material deposited in the vicinity of the channel will not continue downstream and can starve other areas of their sediment supply. The result is a potentially adverse impact at other locations such as erosion.

LAYOUT AND CONFIGURATION

The layout of ports for commercial, military, recreational, and other uses have been widely treated in the literature. Detailed discussions are available in Bruun (1981) and Quinn (1982) among others. It is not the intention of this paper to discuss all aspects of port layout and configuration in detail, but rather to highlight particular factors that should be considered for ports in estuarine situations as they differ from those with granular sediments.

The effect of relatively small changes in current magnitude and patterns in an estuary can have a marked impact on sedimentation rates. Notwithstanding the large-scale changes from dredging of turning basins and channels, the introduction of piers, berths, and other port structures can induce localized changes that may be equally damaging to the maintenance of the facility.

A relatively common structural type for marginal facilities is the relieving type platform shown in Figure 5. These types of structures are particularly common at sites with poor foundation conditions not conducive to gravity structures. In addition, they have the advantage of being economically attractive in many applications. The difficulty with this type of structure, however, is that the pile fields can result in a reduction in current velocity locally with attendant deposition of material in the structure. The result is sediment deposition that eventually spills into the adjacent berth area.

Slip-type berthing facilities have also been widely used in a variety of ports and have the advantage of minimizing the length of channel required for a fixed number of berths. However the parallel structures essentially form settling basins where material is deposited on flood tides, but is not easily removed on the ebb tides, particularly fine-grained materials.

Examples of this type of deposition can be seen in many ports where slips are the norm, i.e., New York. It is not uncommon for loss of depth in such slips to reach 6 to 8 ft/yr under normal circumstances. Deposition in these types of structures is particularly bothersome given the difficulties associated with dredging in confined areas. Arrangement of the berths parallel to the flow can limit the impact of this type of situation, although the approach is not always practical.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 5 Relieving platform.

Solid structures, i.e. caissons, sheetpile cells, etc., can result in local increase in flow velocity and erosion. Restrictions in channel cross section have a similar effect and have been used to advantage, such as at the port of Abidjou where, after a recurring maintenance dredging problem, training structures were added to result in a self-scouring channel (Silvester, 1974).

Upland development associated with a port can also have an adverse effect on sedimentation in that increased drainage contributes a greater sediment load to the port.

EFFECTS OF VESSEL NAVIGATION

Interestingly, the transit of vessels in ports with predominantly fine-grained sediments can serve to clean navigation channels, turning basins, and berth areas of sediments, reducing the amount of maintenance dredging required. This is particularly true in areas where a fluid mud layer exists.

Turns in the navigation channels can exacerbate erosion in the channel areas. The problem is induced by vessels navigating the curve in the channel. Changes in power applied entering, through, and leaving the turn can induce erosion of the bottom of the banks particularly where the radius of the curve is relatively small compared to the vessel size. Vessel traffic, even in straight channels can induce bank instabilities which contribute to sedimentation as a result of ship generated waves at the shore.

Vessels moving in the channel and in and out of berths can also keep materials in suspension until normal currents can move them. An example of this phenomenon is illustrated in Figure 6 for a location in Bahia Blanca, Argentina. Measurements obtained from October 1976 through September 1977 show a distinctly rapid siltation to a depth of

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

about 8.4 m. At this depth, which was comparable to the draft of the loaded vessels in the area, further deposition seems to have halted (PIANC, 1979).

METHODS OF SEDIMENTATION CONTROL

Some alternatives exist that can be considered to assist in the control of sedimentation in port areas. Depending on the particular circumstances, a number of different structural and nonstructural solutions have been utilized with varying degrees of success.

The approach to limiting sedimentation in specific areas is centered on one of three possibilities:

  1. Stop the sediment from reaching the site.

  2. Keep the material in suspension through the site.

  3. Divert the sediment flow from critical areas.

Sediment traps can be utilized to stop sediment from reaching a given area. In their simplest form a pit dredged into the bottom updrift of the port structures can serve to trap some of the material that would normally reach the facilities. Maintenance dredging is facilitated since the location can be controlled. In some instances installation of fixed dredging plants at the location of these traps is possible. The practicality is, however, somewhat contingent on the consistency of sediment flow since the equipment is immobile and significant oversizing may be required to deal with seasonal fluctations.

Sediment supply can also be reduced through the use of bank stabilization of navigation channels as well as upstream segments subject to natural erosion.

A variety of training structures can be considered to increase local flow velocities, thereby keeping material in suspension through a locale. Walls, skirts below finger piers, and even bubbler systems can be used to accomplish this end. The intent is to locally increase flow velocities keeping material in suspension that would normally settle out of the water column. Obviously periods of slack flow can pose a problem for these types of systems, and substantial analysis is necessary prior to their use. For example, bubbler systems have been used with some success in marinas to minimize sedimentation and to reduce icing in northern locations.

Diversion of sediments prior to their reaching a port has also been used to reduce maintenance dredging in harbors. For example, a dike was constructed in the lower part of Newark Bay in the 1930s to divert sediment flow from the Arthur Kill and Kill Van Kull. Significant infilling upstream of the dike is a testament to its early success.

In the Dominican Republic consideration was given in a recent master plan to diverting the Haina River to reduce sediment load and flood damage to the Port of Haina. Although the scheme was not adopted, it is shown for illustrative purposes in Figure 7. Investigations indicated that the river was contributing the largest

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 6 Siltation at Bahia Blanca.

FIGURE 7 Haina River diversion.

proportion of sediments to the port, particularly in the more protected inner areas. The coarse-grained fraction was concentrated in the outer areas of the port, so that a significant saving in maintenance dredging could be anticipated with the diversion of the river. Economically, however, maintenance dredging was a more practical alternative.

In each of the methods of control identified above, one factor must be recognized. Whether the material is trapped, maintained in suspension, or diverted, the maintenance dredging problem is not eliminated, it is simply relocated. While the volume of material to be removed may not be significantly altered by these measures, the location of the dredging can be controlled, thus potentially lowering both cost and environmental consequences of maintenance.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

CONCLUSIONS

While the planning process for ports in fine-grained sediments may differ in some respects from that employed for ports in granular materials, there are many similarities. In planning for the installation of port facilities in estuaries, a number of factors require consideration in terms of their impact on future maintenance requirements.

Minimizing the disruption of the natural flow regime reduces the potential maintenance requirements of the port. Although the problem of maintenance dredging cannot be entirely eliminated in most cases, judicious planning combined with sound engineering can serve to limit its impact.

REFERENCES

Bruun, P. 1981. Port Engineering, 3rd Edition. Houston, Tex.: Gulf Publishing Co.


Ippen, A.T. 1966. Estuary and Coastline Hydrodynamics. New York: McGraw-Hill.


Permanent International Association of Navigation Congresses. 1985. Navigation in Muddy Areas. Bulletin, Permanent Technical Committee II. Vol. 43.

Permanent International Association of Navigation Congresses. 1979. Bahia Blanca and River Ports Terminal Study, Final Report. New York: Dravo Van Houten.


Quinn, A.DeF. 1972. Design and Construction of Ports and Marine Structures. New York: McGraw-Hill.


Silvester, R. 1974. Coastal Engineering II. New York: Elsevier Scientific Publishing Co.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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SEDIMENTATION CONSIDERATIONS IN THE DESIGN OF NEW PORTS OR MODIFICATIONS TO EXISTING PORTS

Jens Korsgaard, P.E.

Parsons, Brinckerhoff, Quade & Douglas, Inc.

Many ports and harbors require periodic deepening to maintain depths for safe operations. In some cases the burden of this maintenance is more than can be supported by the port and as a consequence the port is abandoned or the central treasury of the country has to shoulder the economic burden.

In many such cases the extent of the required maintenance dredging was either not appreciated or grossly underestimated. In other cases an existing port which had been economical when orginally built was deepened to accommodate larger ships, resulting in longer and deeper entrance channels, with consequent increase in maintenance dredging costs.

The purpose of this paper is to briefly discuss some aspects of the problems that confront the practicing engineer engaged in the design of ports and harbors.

ECONOMIC CONSIDERATIONS

When evaluating a port project, the projected maintenance, including maintenance dredging, is often a very important factor to be considered when determining the economical and financial feasibility of the project. Basically the engineer is confronted with three situations when considering the impact of the expected sedimentation on costs:

  1. The maintenance dredging cost is the most important economic factor in determining the viability of the project.

  2. The maintenance dredging cost is important, but even large errors in the estimate cannot render the project unfeasible.

  3. The maintenance dredging cost is not important for viability of the project.

In order to determine the category into which the project falls it is necessary to make a preliminary estimate of the maintenance dredging likely to result. Most disasters have resulted from believing that the project was in the third category when in fact it was in the first.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

When making preliminary sedimentation estimates the following must be kept in mind:

  • In order to make a reasonable estimate, the physics of what is taking place must be understood.

  • The margin of error of the estimate is likely to be as large as the estimate itself.

If the evaluation of sedimentation indicates that the project falls into one of the first two categories, help should be sought from experts in the field and extensive field investigations might be called for. It is obviously better to spend $2 million on studies to determine that the project is not economically viable, than to find this out after having spent $100 million for construction.

TECHNICAL CONSIDERATIONS

A number of technical solutions exist to various sedimentation problems in harbors. This paper presents typical problems, concentrated in areas that are the most troublesome, and includes examples of problems and their solutions.

Sediment Supply Restrictions and Traps

Rivers and estuaries in their natural condition usually have relatively deep channels that vary in depth through the year and often shift in horizontal location. Even thoughout the interior of the estuary may be navigable, access from the sea is often restricted by a bar in front of the estuary. Such systems are often permanently in transition due to seasonal variations in water flow and sediment supply. Once artificial channels are dredged in such a system, nature will try to revert to the original natural state.

This reversion takes place through sedimentation of the dredged channels but can be counteracted by three means:

  1. Cutting off the supply of sediments by reducing the sediment content in the water.

  2. Cutting off the supply of sediment-laden water.

  3. Maintenance dredging.

Usually the first two options are uneconomical compared to the third when considered for the purpose of the port only. However when considered in combination with hydropower schemes, irrigation projects, or flood control projects, upstream control dams may be feasible. Upstream dams have the following effects:

  • For a number of years, sediment content in downstream waters is reduced due to retention in the lake behind the dam.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
  • The flow has less seasonal variation, with increased minimum flow and reduced maximum flow.

Both of these factors tend to reduce sedimentation; in addition, the second tends to increase the minimum depth available in the low flow season. This principle has been applied in the port of Hamburg, West Germany, for example through the regulation of the Elbe River (Anderson, 1964).

The sediment content of the water reaching the port can also be reduced by constructing an upstream sediment trap. This procedure has the advantage of removing the maintenance dredging operations from the working port. However, it usually results in larger quantities to be dredged compared to maintaining the port area proper, and further it does not completely eliminate sedimentation in the port. This procedure is only rarely applied since the cost of the increased quantity to be dredged causes it to be uneconomical, the operational advantages notwithstanding.

Diversion of Flow

In cases where the water has alternative means of flowing to the sea, sedimentation in the port area can be reduced by isolating the port system at the upstream connection. This solution was considered for the port of Haina, Dominican Republic but never implemented (Schmeltz, Ibid). The procedure was implemented for the port of Guayaquil, Ecuador, which was built on a nearly isolated arm of the Guayas River delta. The arm was subsequently isolated and connected to the river at the upstream end by means of a lock (Figure 1).

Current Velocity Modification

This procedure is often used where the flow has only one path such that flow volume is not changed by modifications. Where the water has multiple paths, current velocity modification should be very carefully considered so that adverse consequences do not result. Since increased depth is the objective, this can only be achieved through an increase in current velocity by reducing the width of the flow. An overall reduction of the flow area is required, which, for example, can be evaluated by the Manning formula. This procedure is both a very common and very successful one for making estuaries and waterways navigable. The means by which the width can be reduced are covered later.

The fact that this process is not always straightforward can be witnessed from the history of the entrance to the port of Barranquilla, Columbia. This entrance is the main outlet into the Carribean for the Magdalena River. In the 1950s, a trained entrance to the port was constructed from the Caribbean. Based on extensive model tests a width of 850 m was constructed, which according to the tests, would provide

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 1 Port of Guayaquil, Ecuador.

for sufficient natural depth without maintenance. Nature however did not oblige and and a new training dike had to be constructed reducing the width to 500 m which solved the problem of shoaling seaward of the entrance (Figure 2).

Salinity Modifications

Deepening of entrance channels causes deeper penetration of salt water into an estuary for two reasons:

  1. Outward flow velocity is reduced, reducing the retarding forces on the salt water wedge.

  2. Depth is increased, thereby increasing the hydraulic head caused by density differences.

Clay particles carried by fresh water tend to flocculate and precipitate when encountering salt water. Thus, deepening of an entrance channel can both move the location of the sedimentation upstream and increase its magnitude. This can be counteracted by increasing the current velocity at some location downstream such that the saltwater wedge is kept downstream of the restriction. This remedy is not feasible at locations with a significant tidal range where the flow normally reverses in the tidal cycle, nor is it feasible at locations with insufficient river flow. This author is not aware of projects where salinity modifications have been attempted to avoid sedimentation.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 2 Port of Barranquilla, Colombia

Wave Height Modifications

The shear stresses determining the stability of the seabed orginate from a combination of the current and the orbital velocity of the water waves. However, inside a river or estuary the waves are usually too short to have significant orbital motion at the bottom of navigation channels and thus are not important for the stability of the channel. They do however have a significant influence on the general sediment content of the water if there are extensive shallow mud flats where even small waves break. In such cases there is a high correlation between the wind velocity that generates the waves and the sediment content of the water. There is no practical way to deal with this phenomenon, except by establishing vegetation on the mud flats.

At open coast harbors, water waves are often the driving mechanism for sediment transport through nearshore wave-driven currents which, when combined with the turbulence created by breaking waves, are responsible for littoral drift. This sediment transport mechanism is well known. Another often ignored mechanism for sedimentation in open coast harbors is that created in the lee of a breakwater. Breakwaters create relatively calm waters behind the breakwater, thereby reducing the height of breaking waves on the coast in the lee of the breakwater. The breaking waves raise the mean water level shoreward of the breaker zone, thus a hydraulic gradient is created setting up a

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

longshore current toward the harbor along the shore. This gradient only exists during periods with high waves, when the sediments are brought in suspension and large accumulations can result in the harbor.

This phenomenon was observed at the harbor of Marsa El Berga in Libya where a sedimentation rate of 300,000 m3/yr was experienced following the construction of the breakwater in 1967, (Van Houten Associates, 1970). This was unexpected as the littoral drift was on the order of 30,000 m3/yr (Figure 3).

Several solutions were evaluated, and the problem was effectively solved by placing a 150 m long groin perpendicular to the shoreline extending beyond the breaker zone. The groin acted as a dam against the longshore current, preventing the current and hence the sedimentation.

Enclosures and Barriers

Many British and French ports are enclosed by locks that maintain a high water level in the port. This in done to avoid the problems associated with large changes in tide levels in order to maintain sufficient depth in the port. While probably not a consideration when these projects were planned, this isolation also shields the port area from sediment-laden water and only the quantities admitted during locking carry sediments into the port.

FIGURE 3 Harbor of Marsa El Berga, Libya.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

To consider the possibility of enclosing the port and using locks requires an economic evaluation of the cost of constructing and operating the locks plus the added cost to ship waiting time versus the reduced initial and maintenance dredging costs.

While locking is an effective solution to sedimentation problems, it is not likely to be considered today because of the very high construction costs of the enclosure and locks.

Other types of barriers have been considered, such as near-bottom bouyant “silt curtains” to prevent density driven bottom currents, and opposing water jets injecting just sufficient momentum into the water to counteract and neutralize the density driven currents. While these devices may work from a theoretical point of view they are doomed in practice because once in a while an anchor is dropped during ship maneuvers that destroys either the jet system or the curtains.

Bank Stabilization

In some cases the sources of the sediments causing the sedimentation are nearby banks or shores. This was the case in the previous example of Marsa El Berga, Libya. Several actions are possible:

  1. Protect the bank by parallel or angled training walls or revetments.

  2. Do nothing and await the maximum erosion of the banks after which time the sources can no longer supply sediments.

  3. Protect the banks by natural or planted vegetation.

The second option was employed in a project at Zawia, Libya. It was known that the rocky shores that could supply sediment to the harbor contained approximately 20,000 m3 of sand. This quantity entered the port within 3 months, after which further sedimentation stopped.

In most cases it is not economically feasible to protect all banks that can supply sediments to the project, as compared to adopting other measures previously discussed. However, in the case of valuable land being eroded away because of the project, legal liabilities may exist that become overriding factors.

Current Training Devices

To regulate the width of a channel in a river or estuary, physical devices must be constructed that effectively narrow the channel. Two types are common: parallel training walls or dikes, and angled walls encroaching on the flow. Each principle is illustrated in Figure 4.

Angled walls have the advantage reducing the width of the channel by lengthening each wall, whereas parallel walls require an entirely new wall when a new channel width is needed.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

In some cases it is possible to take advantage of the natural tendency for erosion on the outer side of bends in the waterway. In such cases maintenance dredging at the berth can be avoided by constructing at the location with the largest natural depth (Figure 5)

FIGURE 4 Parallel training walls (a) and angled walls (b).

FIGURE 5 Areas of largest natural depth.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

CASE HISTORY OF A PORT ABANDONED DUE TO EXCESSIVE SEDIMENTATION

Puerto Rosales, Argentina

This port, formerly known as Puerto de Arroyo Pareja was constructed by a French consortium in the bay of Bahia Blanca, Argentina. On September 15, 1908, the consortium received a 60-year license to construct and operate a port with 5 km of wharf. Roughly one fifth of the port was constructed between 1908 and 1914. The plan was straightforward—to construct part of the port, put this part in operation and then use the revenues to slowly expand the port to its full capacity. Modular construction was to be employed using a standard caisson type for all wharves. The harbor basins were to be dredged from the mud flats that were the natural environment in the area of the port. Due to unique and uniform soil conditions the modular construction concept was entirely feasible. The port was planned for a uniform depth of 30 ft.

Construction of the port was started by procuring a dredging plant consisting of one bucket dredge and two bottom dump barges. At the same time a concrete caisson construction plant was erected. It was planned that after opening the port for commercial activity early in the construction period this plant would complete the port.

The plan was feasible except for one problem; there was no provision for maintenance dredging. It was assumed that sedimentation in the port would be negligible. The initial part of the port was opened as required by the concession. By then World War I had broken out, making it impossible for the consortium to raise additional funds. Contrary to expectations the sedimentation rate in the port was about 1 ft/mo, so the dredging plant had to be employed exclusively to keep the already-opened section in use, making further expansion of the port impossible without additions to the dredging plant. Additions were impossible due to lack of funds, and the port did not generate sufficient revenues to finance the expansion from internal funds.

The concessionaire limped along trying to keep the project alive until the economic depression of the 1930s finally forced the concessionaire to give up. The project was given to the government of Argentina, which made several attempts to reopen the port by performing the necessary dredging. Each time the reopening was short-lived because of the high rate of sedimentation. The port is today only used by shallow draft fishing vessels. The present condition is shown in Figure 6, in which the initial part can be seen completely silted in.

CONCLUSIONS

Calculation of expected maintenance dredging in ports and harbor projects is one of the most uncertain aspects of the design process. History shows many examples of projects which failed or had a much reduced financial return due to major miscalculations of sedimentation rates. A few such cases are illustrated in this paper.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

A number of different sedimentation problems are shown with possible remedies. It is stressed that proper understanding of the physical processes causing the sedimentation in each case is an absolute requirement for proper calculations.

FIGURE 6 Port of Rosales, Argentina.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

REFERENCES

Armada del Ecuador, Direccion de la Marina Mercante y del Litoral Estructura Portuaria Ecuatoriana, June 1980, (in spanish).


Communications with Direccion Nacional de Construciones Portuarias y Vias Navegables, Buenos Aires, Argentina (not published).


E.J.Schmeltz, Planning Considerations for Ports in Cohesive Sediments, Ibid.


J.Korsgaard, Report on Inspection of the Entrance to the Magdalena River in Columbia, Boca de Cenizas—Observations Made on March 3, 1983, Danish Hydraulic Institute, Copenhagen, Denmark 1983 (not published).


Primer Congreso Nacional de Ingenieros, 23 de Septiembre a 8 de Octubre 1916, Centro Nacional de Ingenieros, Seccion Vias de Communicacion, Subseccion: Navegacion pp. 674–675, Buenos Aires, Argentina, 1919 (in Spanish).


Van Houten Associates Inc. (now Dravo Van Houten), Siltation Study for Harbor at Marsa El Berga, Sept. 1970, for Esso Standard Libya, Inc.

V.Mandrup Andersen, Vandbygning II (Hydraulic Structures II), Akademist Forlag, 1964, Copenhagen, Denmark (in Danish).

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

NEW FACILITY DESIGN ISSUES AS CONSIDERED BY MARINE TERMINAL USERS

C.Lincoln Crane

Exxon International

Richard B.Harley

Exxon Research and Engineering Company

For most industries, marine terminals are simply a means to an end, such as receipt of raw materials or delivery of finished products. Since terminals provide little opportunity for positive cash flow, a primary objective is usually to minimize associated costs without affecting safety or reliability.

Traditionally, the accumulation of sediments at terminals is controlled by maintenance dredging, which is absorbed as an operating cost. Usually, relatively little design work is done to definitively reduce this cost. While operability and safety issues are typically recognized and resolved, the practical advancement of sediment control technology must also address the economic criteria against which new proposals for facility design will be evaluated. For a ship, the key economic factor is allowable vessel draft, which determines how much cargo can be carried. For the shore facility, the cost of maintenance dredging and any alternatives are significant factors. Operability and safety issues that affect both the ship and shore include project feasibility, probability of touching bottom, and effects of sediment on ship maneuvering, intake manifolds, and mooring.

PROJECT FEASIBILITY

Feasibility is a leading issue that needs to be addressed in designing a new port facility. While cost trade-offs are normally not addressed in the feasibility planning stage, the ultimate criterion for feasibility is often whether a project can be done at reasonable cost. In the case of sediment deposition, any early assumption about reasonable costs can potentially be invalidated if appropriate site-screening investigations are not carried out.

In 1968, Exxon had to abandon a terminal site at Benicia, California, after dredging 1 million m3 for a new pier. The site is just upstream from Mare Island on Carquinez Strait in the San Francisco Bay area (Figure 1). In hindsight, the location shows a definite potential for sedimentation because it is on the inside of a bend, in the shadow of another pier, and in an area of eddies and shearing that promotes flocculation of the clay sediments that are

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

available from multiple sources. Still, prior examination of historical soundings, work by technical consultants, and discussions with local authorities did not reveal any concerns.

In fact, the site filled in at the pierhead line from a depth of 35 to 17 ft in 4 months. As a result, a substantial premium was paid for temporary use of an existing pier until a reasonable alternative could be found. Ultimately no reasonable solution could be found, largely because construction in deeper water beyond the pierhead line was not allowed, and the temporary pier became a permanent facility.

WATER DEPTH, ALLOWABLE VESSEL DRAFT, AND ITS VALUE TO THE USER

Water must exist between the ship’s keel and the waterway bottom for a ship to move, maneuver, avoid damage, and not be stranded. This allowance is called underkeel clearance. However, increasing the required underkeel clearance reduces allowable vessel draft and the carrying capacity of the ship. Factors determining underkeel clearance are related to the ship’s motions, the water level, and the waterway bottom (Figure 2). To properly determine underkeel clearance, all the factors depicted in Figure 2 must be quantified.

FIGURE 1 Benicia product loading pier.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 2 Factors used to determine net underkeel clearance: deterministic approach.

The “channel dredged level” includes an allowance for the limited accuracy of soundings and the dredging tolerance. Where siltation or other bottom changes occur, an allowance for sediment deposit between successive maintenance dredgings or sounding surveys must also be included. Siltation can be accounted for if rates are known. However, if siltation rates are not known, uncertainty or deviation must be included to account for possible depth reduction due to siltation. In fact, most of the ship and waterway factors which contribute to the required allowance for underkeel clearance are not known accurately enough for unqualified channel design or ship operating analysis. The uncertainties are classified as relating to either predicting the behavior of a ship sailing under given conditions, or the inability to accurately define these conditions. The analysis must therefore be balanced against practical experience. Most marine operations and design decisions are based on experience. However, analysis can usefully supplement experience in these matters.

In the conventional deterministic approach, the underkeel clearance factors shown in Figure 2 are directly combined using addition and subtraction. This approach was described by the Committee on the Reception of Large Ships of the Permanent International Association of Navigational Congresses (PIANC, 1980). They used

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

“maximal” numerical values, so their results tend to be conservative. Figure 2 suggests how these factors are combined. Notice that water depth, for example, is corrected for known or estimated sediment deposits. After all factors are accounted for, an additional allowance may be applied to cover unknowns or uncertainties that aren’t considered. The remaining portion of the water depth should then be available for the ship to maneuver over.

In the probabilistic approach, the uncertainties of ship behavior under given conditions, and the conditions themselves, are considered for determining underkeel clearance. The variances of the factors are added together and combined with the average, or steady, values of the factors, as shown in Figure 3. Using statistical rules, the required underkeel clearance is then calculated for a very low target probability of the ship striking the bottom. To make it practical, simplifications reduce the procedure to a relatively few arithmetical steps.

A semi-probabilistic approach was presented by Kimon (1982) for tankers operating in virtually any hard-bottomed port area, including

FIGURE 3 Factors used in probabilistic approach to determining underkeel clearance mean values plus variances.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

an offshore fairway with waves or swell present. Under the method’s restrictions of nonchanging boundary conditions, such as found in selected fairway reaches and in the absence of waves or swell, the underkeel clearance (UKC) is given by

Kimon states that each of the variances is obtained from observations or calculation, and is normally distributed. By reducing the data to graphic form, it is simple to obtain a value for each variance factor. The squat factor added on the right side of the expression represents the average value for a given operating condition (e.g., in shallow water or near a bank or passing ship). Assumptions are made that the different factors are normally distributed and independent of each other, and that the waterway bottom is flat. These are generally acceptable assumptions for a preliminary assessment, but for specific circumstances they might not be acceptable; for example, where large siltation variances or a very uneven seabed exist. In the case of soft bottoms, and where much vessel experience exists, experience factors may overrule the analysis. The procedure described by Kimon also accounts for the effects of the ship motions in waves on underkeel clearance.

The above sum represents the required underkeel clearance. To obtain maximum permissible draft, the required underkeel clearance is subtracted from the nominal water depth (i.e., charter depth plus-or-minus tide allowance, minus siltation, plus undercut).

Figure 4 is an example input data sheet for a calculation of required underkeel clearance for Exxon’s Fawley Refinery terminal, near Southhampton in the south of England. Figure 5 is the associated k coefficient calculation worksheet. Recall that k is the required underkeel clearance value, less the combined variance due to all uncertainties except for squat, which is added separately.

The 1986 report of the NRC Marine Board Committee on Advances in Environmental Information Services for Ports discusses the value of additional draft if allowed by on-line reports and short-term forecasts of water levels in ports. The factors are discussed for typical container vessels, tank vessels, tug barges, and bulk carriers. A caveat of using water level information to increase allowable draft is that considerable forecasting lead time would be necessary to enable increased vessel loading with confidence. However, the problem is much reduced where increased water depths can be maintained through control of sediments. The numerical values provided in the above Marine Board Report for increased revenue per 1 ft of draft of representative vessels calling at U.S. ports are summarized below:

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 4 Underkeel clearance input data sheet.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 5 Coefficient calculation worksheet.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

Vessel

Size

Drafta

TPIb

Additional Revenue Pier 1-ft Draftc

Container Vessel

750 ft LOA

-

120.0

72–288

Tank Vessel

30,000 dwt

36′–2″

108.8

16–22.5

 

50,000 dwt

40′–7″

150.8

17–22.5

70,000 dwt

43″–3″

179.0

20–26.7

120,000 dwt

51′–9″

253.9

23.6–30.6

Tug Barge

30 bbl

-

-

1

a Draft when fully loaded

b TPI is tons per inch immersion

c Thousands of dollars

MAINTENANCE DREDGING COSTS AND WHAT THEY CAN BUY

The cost of maintenance dredging clearly represents an incentive for capital expenditures to reduce sedimentation. The intent would be to reduce operating costs such as dredge mobilization, berth down time, and actual dredging. At the same Fawley marine terminal previously cited, Exxon spends about $300,000–400,000 per year just to maintain depths at the upstream berths (Figure 6). In addition, down-time berths while dredging is taking place might cost $100,000–200,000 in ship delays and demurrage. The Fawley terminal staff is currently evaluating alternatives to conventional suction dredging that may be more economical, such as use of vortex foils moored near the bottom to keep sediments in suspension. An issue at the moment is satisfying local authorities that there will be no significant downstream effects.

It is important to make a note, however, about the Fawley situation, and any other case in which initial dredging for a particular ship size has already been completed. In such cases, the economics of handling large ships for which dredging is already complete may not fully apply as justification for reducing sedimentation. They would apply only if ship draft has to be periodically reduced due to sediment deposition. Often, however, an overdredge allowance precludes the need for adjusting draft. In such instances, methods for reducing sedimentation must be justisfied primarily by the lower cost of maintenance dredging that will result.

Exxon investigated these incentives in a study aimed at evaluating alternatives to conventional maintenance dredging in berthing areas.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 6 Fawley Marine Terminal.

The results are shown in Figure 7, which summarizes the associated economics. The graph shows that sediment accumulation and dredging costs need to be substantial to justify energized systems such as eductors or jets. On the other hand, passive systems such as silt curtains or vortex foils could prove to be economically viable.

PROBABILITY OF TOUCHING BOTTOM

Only a very small probability of grounding on a hard-sand or rocky bottom can be considered acceptable. For that reason only 1 touching in 10,000 transits was suggested as a tolerable risk by Kimon (1982). The consequences of touching a soft bottom are much less, however. Touching may be hardly noticed, and a minor stranding may amount to little more than some embarrassment and nuisance. Some pilots have suggested that if unnecessarily large underkeel clearances are kept

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 7 Evaluation of alternatives to conventional maintenance dredging. *A particular system is justified if, for the average annual sediment accumulation occurring at a site, the unit cost of conventional maintenance dredging exceeds the value depicted by the above graph. The justification is based on a required rate of return of 15 percent and typical application of the alternative systems. Applicability may also be limited based on soil type, pier configuration, current velocities and directions, or energy costs.

over silted bottoms, existing bottom clearance will disappear all the more quickly.

Entry to the port of Las Salinas, in Lake Maracaibo, Venezuela, requires transiting of a long silted channel extending from offshore and through the entrance to the lake. Light silt abounds, and loaded vessels frequently “smell” the bottom or even experience deceleration. Shipmasters sometimes record the sounder readings, and refer them to their main offices for help in selecting drafts for loading. Modest ship speeds are also maintained. However, the consequences of a trifle too little underkeel clearance are usually not severe.

OTHER RELIABILITY AND SAFETY ISSUES

Ship handlers have long appreciated that restricted underkeel clearances affect maneuverability, but the degree was not well quantified until the 278,000 dwt Esso Osaka underwent a series of

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 8 Water depth effect on turning circle paths.

maneuvering trials in the Gulf of Mexico (Crane, 1979). Effects of underkeel clearance on turning circles and stopping are shown in Figures 8 and 9 respectively.

Modern self-polishing hull coatings are soft and easily worn if subjected to frequent or prolonged exposure to much silt in the boundary layer of the bottom. On the other hand, there is also a bottom cleaning effect of silt, which can be useful to a harder-coated bottom if a vessel trades regularly into such waters. In that case, it is impractical to apply expensive and soft hull coatings to a vessel’s bottom.

Sediments ingested in a vessel’s seawater intake may plug the saltwater tubing of condensers and coolers. For this reason many vessels are provided with high and low intakes; i.e., one in the bottom for deep water, and one in the side above the double bottom height for shallow water. This system alleviates the problem, as long as the crew remembers to shift intakes upon entering port. If plugging of a main condenser of a steam vessel does happen, the crew may be able to clear it, but the vessel will have to shut down for a day or two.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

For large oil tankers, the loads created on the ship by wind and currents require special attention to the capacity of the mooring lines. The loads due to currents are aggravated when siltation reduces the underkeel clearance of the vessel in berth. Figure 10 shows that the current force coefficient (OCIMF, 1977) increases dramatically when reduced underkeel clearance (water depth to draft ratio) restricts current flow under the tanker hull.

FIGURE 9 Water depth effect on stopping path.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 10 Lateral current force coefficient.

At Exxon’s crude oil unloading pier in Benicia, California, siltation occurs in the area where moored ships are often subjected to significant current loads. The mooring loads are worsened when siltation has reduced the underkeel clearance. It is suspected that the siltation may have been a contributing factor when two vessels nearly broke away from the berth when mooring lines were overloaded.

REFERENCES

Crane, C.L. Jr. 1979. Maneuvering trials of a 278,000 dwt tanker in shallow and deep water. Trans. SNAME.


Kimon, P.M. 1982. Underkeel clearance in ports. Ship-Trans-Port Symposium, Rotterdam.


OCIMF. 1977. Prediction of Wind and Current Loads on VLCC’s. London: Witherby and Company, Ltd.


Permanent International Association of Navigational Congresses (PIANC). 1980. ICORELS: Final Report Bulletin No. 35, Vol. I.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

NEW FACILITY DESIGN CONSIDERATIONS: FOR FORMULATING A DATA BASE

Glenn A.Pickering

Hydraulics Laboratory

U.S. Army Engineer Waterways Experiment Station

The purpose of this paper is to summarize and familiarize planners and designers with resources available for the layout and design of a new port facility. The object of the paper is not to present detailed design information, but rather to furnish the designer with factors that need to be considered, and to direct them to where this detailed information can be found or how additional information can be generated when needed. In doing this it will be impossible at times to totally segregate generalities and details. There will, no doubt, be an overlap of information contained in this paper with material presented in other papers at this symposium.

I will assume that the designer has limited experience in facility design and is given the task of determining if a given location is feasible for construction of a facility, and if so, to design the various elements of the facitity. Design of a project requires an understanding of the problems and factors that affect the design, and evaluation of all pertinent facts. In many situations there will be no right or wrong solution, only a degree of adequacy.

Before undertaking a problem as vast and complicated as locating and designing a port facility, the designer would be well advised to study publications pertaining to the subject. An excellent start would be the book Port Engineering (Bruun, 1976).

FACILITY LOCATION

Prior to the design and layout of a facility, one must first determine the feasibility of the desired location. A port should not be located on a shore with heavy erosion and littoral drift or where heavy accretion occurs. Ports have been built in areas where it was impossible to maintain an open harbor and entrance channel, and exposed shores, where they were destroyed by the sea. Examples of such ports are shown in Bruun (1976). Thus it is very important to be able to predict the amount of littoral drift and shore erosion at a particular site.

The Shore Protection Manual (U.S. Army COE, 1984), presents the current state of the art of coastal engineering and provides guidance

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

for solving coastal design problems. Section VIII of Chapter 4 of the manual discusses the engineering study of littoral processes. In order to study the littoral process one must first obtain pertinent data. If the area is located on a U.S. coastline, the Report on the National Shoreline Study (U.S. Army COE, 1971), can provide a general description of the area and may give some indication of the littoral processes occurring in the vicinity of the problem area.

Historical records of shoreline changes are usually in the form of charts, survey profiles, dredging reports, beach replenishment reports, and aerial photographs. An example of such data is shown in Figure 1, taken from the Shore Protection Manual (U.S. Army COE, 1984), which shows the position of the shoreline of Sandy Hook, New Jersey, during six surveys from 1835 to 1932. Such shoreline change data are useful for computing longshore transport rates. In its district and division offices, the Corps of Engineers maintains survey, dredging, and other reports relating to Corps projects. Charts may be obtained from various federal agencies including the Defense Mapping Agency Hydrographic Center, Geological Survey, National Ocean Survey, and Defense Mapping Agency Topographic Center. A map called “Status of Aerial Photography” (which can be obtained from the Map Information Office, Geological Survey, Washington, D.C.), shows the location and types of aerial photographs available for the United States and lists the sources from which the photographs may be requested. Other kinds of data usually available are wave, tide, and meteorological data.

FIGURE 1 Growth of Sandy Hook, New Jersey, 1835–1932.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

A field study of the site is usually necessary to obtain types of data not found in the office study, to supplement incomplete data, and to serve as a check on the preliminary interpretation and correlations made from the office data. Information on coastal processes may be obtained from wave gauge data and visual observations, sediment sampling, topographic and bathymetric surveys, tracer programs, and observations of effects of natural and man-made structures. After the necessary data have been obtained, they can be used to make sediment transport calculations and a sediment budget. Methods for making these calculations are shown in the Shore Protection Manual (U.S. Army COE, 1984). Knowing the transport rates, historical problems at the site, and other pertinent data, one can make a decision as to the costs, time and equipment required to maintain the facility, or if it is possible to maintain a facility at all at a particular location.

Chapter 7 of Port Engineering (Bruun, 1976) lists ten demands in coastal geomorphology versus port engineering, which provide good guidance for siting a port with respect to such factors as littoral drift, currents, and coastline shape.

FACTORS TO BE CONSIDERED

Once it has been determined that a facility can feasibly be located in the desired area, several elements must be designed and there are numerous factors that will influence the design of each of them. These factors must be identified and data compiled for use in making decisions.

Design Vessel

Selection of the design vessel(s) will depend on the amount and type of traffic that will use the facility. It is identified by dimensions, maneuverability or controllability, speed, and type of cargo. There may be situations in which the design vessel will be a large vessel that is loaded to less than its full capacity. It is selected after an economic analysis involving construction and maintenance costs to accommodate various vessels. An examination of general trends in the classes of vessels involved, the depths of other ports that vessels will use, and other site-specific requirements should be made. Data on general trends of vessels can be found in the Bruun (1976) and U.S. Army COE 1971 and 1961a.

The Maritime Administration maintains a series of Maritime Data Network (MARDATA) libraries that contain pertinent vessel characteristics for the world fleet. Data for these libraries are furnished by Lloyd’s Register of Shipping, Ltd., and are continuously updated.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Weather

Wind, waves, visibility, and ice will significantly affect the design of various elements of a project, as will vessel motions and controllability, sediment erosion and deposition, and the extent and characteristics of salinity intrusion. Wind data are available from the Department of Commerce National Climatic Data Center. Information should be coordinated with the U.S. Coast Guard for any particular problems affected by local topography or features.

Wave heights, periods, and direction can be obtained from prototype observations and computed using wind records. Methods for predicting wave information are discussed in Chapter 3 of the Shore Protection Manual (Bruun, 1976). Wave information for various areas in the United States can be obtained from a series of reports called “Wave Information Studies of U.S. Coastlines” (continuing series).

Smog, fog, and snow will affect visibility and at times result in delays because vessels will be unable to transit the channels. These factors are unpredictable on a daily basis, but general information for the area can be obtained from local records and the U.S. Weather Service.

Hydraulics

Tides affect water levels and information about them are needed to design channel depths. The National Ocean Service (NOS) publishes tide height predictions and tide ranges. Published tide predictions are sufficient for many channel designs; however, prototype observations are often required.

Currents affect maneuverability of vessels, sediment movement, and water depths. Currents are caused by tides, tributary streams, and/or river discharge. Tide current predictions are published by NOS. River discharge data are published by the U.S. Geological Survey. Local surveys and field data may be required to obtain discharge and current data for small local tributaries that can affect design.

Salinity will affect the draft of vessels, currents, and shoaling. Changes in channel dimensions can change the degree of salinity and sediment movement. The salinity of a tidal waterway varies greatly, both areally and vertically at a given time, and as to time at a given point by both short time cycles and long periods. Thus prototype observations to obtain salinity samples must be obtained over a large area for a long period of time. Guidance for salinity sampling is provided in “Environmental Engineering for Deep-Draft Navigation” (U.S Army COE, in preparation).

Physical Characteristics

Physical characteristics that influence design include type of bottom material, sediment size, natural channel alignment and configuration, possible dredge disposal areas, bridges, powerline

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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crossings, underground utilities, and other obstructions such as sunken vessels and abandoned structures. This information can be obtained from maps, aerial photographs, and field measurements.

Environmental

Construction of new facilities usually involves removal or relocation of large volumes of bottom sediment and resultant changes in bottom geometry. Environmental considerations associated with this construction include those related to dredging and disposal of dredged material, and the possible alteration of water circulation patterns, water levels, flushing rates, etc. Changes in water quality and biological populations can result. “Environmental Engineering for Deep-Draft Navigation” (U.S. Army COE, in preparation) provides guidance for incorporating features in projects to attain environmental quality objectives.

ELEMENTS TO BE DESIGNED

After gathering and analyzing pertinent data concerning factors that influence design of a facility, and making decisions concerning the type of traffic and vessels that will use a port, one can proceed to the layout and design of the various elements for the project. Layouts should be prepared using various channel alignments and dimensions, and each layout should be evaluated on the basis of tonnage moved, trip time, safety, environmental and social impacts, and construction and maintenance costs. Comparison of costs to benefits will indicate the most economically feasible layout for the specific project.

Channel Design

The navigation channel is usually separated into two sections: an entrance channel and the interior channel. The entrance channel is exposed to more severe weather conditions (wind and waves) that will affect motions of the vessel (pitch, roll, yaw, heave, etc.). Elements of the channel design include depth, width, and alignment. Optimum placement of aids to navigation will affect channel width and alignment. This should be coordinated with the Coast Guard.

Adequate channel depth is the first requirement of safe navigation in a waterway. Channel depths substantially greater than the loaded static drafts of the vessels using the waterway are required in order to ensure safe and economical navigation. Therefore, in the design of a channel, the minimum depth must be considered first, then width and other requirements. The depth should be based on the draft of the design vessel, sinkage due to squat of the vessel, sinkage in fresh water, effect of pitching and rolling of the vessel, and safety and

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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efficiency clearance underneath the keel of the vessel. The draft of the loaded vessel will be determined during the selection of the design vessel as previously discussed. Methods for determining the sinkage due to squat, fresh water, pitch, and roll are shown in various publications. Two of these are “Layout and Design of Deep-Draft Navigation Projects (U.S. Army COE, 1983b) and “Evaluation of Present State of Knowledge of Factors Affecting Tidal Hydraulics and Related Phenomena” (U.S. Army COE, 1965a).

Safety and efficiency clearances are a function of the type of material on the channel bottom. There is a great difference between touching soft fluff and striking rock bottom. A clearance of at least 2 ft should be provided between the bottom of the vessel in motion and the channel bottom to avoid damage to propellers from sunken timbers and debris and to reduce displacement of the bottom material. When the bottom of the channel is hard this clearance should be increased to 3 ft. Since the static draft of the vessel may be different in entrance channels and interior channels due to the salinity of the water, and wave action may cause the vessel to roll and pitch more in entrance channels, a greater depth may be required for the entrance channel than the interior channel for the same design vessel.

In designing a channel, the impact of proposed deepening on sediment transport and maintenance dredging requirements should be considered. Advanced maintenance (overdepth dredging) should be evaluated to determine its effectiveness in reducing dredging frequency (U.S. Army COE, 1983b and 1965a). Channel width depends, on design vessel size and maneuverability; channel shape, alignment, depth, and whether it is in a restricted or wide waterway; wind, waves, currents, and visibility; and type and spacing of navigation aids. There is no formula or equation that takes all of these factors into account; however, guidance is available based on investigations made during the study of the proposed sea level Panama Canal and verified during physical model studies at the Waterways Experiment Station (Turner, 1984).

Channel width is divided into maneuvering lanes, clearance between vessels when passing, and bank clearance (Figure 2). The recommended width of each of these sections is based on controllability of the vessel (very good, good, poor) in ideal weather and hydraulic conditions. Judgment is required to determine the additional width of the maneuvering lane required where yawing forces will be encountered or where weather conditions affect visibility.

Curves or bends in the channel are more difficult to navigate than straight reaches, thus the channel must be widened at bends to assure safe navigation. Bends can be widened using the cutoff method or parallel bank method (Figure 3). Some limited guidance on the amount of widening required was provided from the Panama Canal study is included in U.S. Army COE (1983b). A physical model study underway at the Waterways Experiment Station to provide additional data on bend widening includes testing of bend angles of 30, 45, and 60 degrees with slack water and with various currents. Both the cutoff and parallel bank methods of widening are being tested. These tests will be completed in 1987.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 2 Interior channel width elements.

FIGURE 3 Two methods of channel widening.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Navigation in entrance channels is often adversely affected by strong variable tidal currents, rough seas, breaking waves, wind, fog, and other difficulties. Safe navigation will generally require an entrance channel much wider than that of the interior channel since control under such conditions tends to be difficult. Channel widths in entrances will have to be judiciously selected based on an analysis and evaluation of conditions at each project.

In order to minimize initial and maintenance dredging, the alignment of the navigation channel should follow the course of the deeper channel in a river or estuary as much as is practical. However, the overriding requirement for channel alignment is that all vessels expected to use the channel be able to navigate with reasonable safety under adverse conditions of tide, current, and wave and wind action. Consequently, the minimum permissible radius of curvature or maximum deflection angle at bends is governed by the turning characteristics of the least maneuverable vessel, which in some instances may not be the design vessel. Widening at bends has been discussed previously.

In selecting the alignment for a new or improved channel, the designer must balance the anticipated benefits from straightening against those of following the natural alignment, or a compromise between the two. The cost of maintenance for various alignments must be considered in addition to the initial costs to determine the most economical cost. Changes from the natural cross section and alignment invite conteractions by nature.

Critical locations for a vessel navigating a channel are at the ocean entrance, bridges, and approaches to locks, barriers, and control structures. Straight approaches, long enough for vessels to become properly aligned are a necessity in these areas. In these channels, vessels may encounter strong currents and transverse wind and wave action. A straight entrance channel parallel to the resultant of these forces is generally safest for navigation, but shoaling influences frequently require adjusted alignment to obtain economic maintenance.

Physical and/or numerical ship simulation models can be used to assess the safety of various channel widths and alignments. These tools can be very valuable in assisting designers in solving site-specific problems.

Ship and tow simulators have been developed that enable researchers to study the interactions of man, vessel, and environment. A test scenario is developed for channel design alternatives and conditions: e.g., flow rates, tidal conditions, wind, visibility, and navigation markings, and test runs are conducted through simulated conditions. As the vessel is navigated through the test area, it is subjected to forces resulting from the environmental factors and its motion is determined. As it progresses through the scene or changes orientation, a computer-generated view from the pilot’s window is displayed on a screen. Key navigation information is also displayed on a precision navigation display. Data pertaining to the ship’s motion, location, and orientation in the test area are recorded for later analysis. A tracking of the vessel through the test area is recorded during the simulation run for immediate evaluation of the results.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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In order to create the simulation of vessel maneuvers through a particular study area, certain data must be available. Unique coefficients must be available for the design vessel for use in the mathematical model that computes the vessel hydrodynamics and vessel response to the external forces and the vessel controls. These coefficients must be developed from physical models in towing tanks and correlated with prototype tests when possible. A good description of the channel dimensions and the bottom topography of the area to be tested is needed. Recent hydrographic surveys are very valuable for this purpose, as well as charts with the dimensions of the channel and the heading of the channel center line. For the generation of the visual and radar scenes, detailed maps, of the general area including land masses and principal features such as major buildings, bridges, other landmarks, navigation aids, and range markers are needed. This information can be obtained from aerial photographs, maps, and photographs of the area as seen from a vessel transiting the area.

Simulations can be used to study such factors as channel depth, bottom width, presence and layout of banks or other obstacles in or near the channel, turning basins or anchorage areas, alignment of the channel, presence of navigation aids, location and alignment of bridges, and locks and other physical obstacles in the waterway.

A tow and ship simulator has been developed and placed into operation at the Waterways Experiment Station. Information pertaining to this facility and an inventory of vessels and areas that can be simulated is shown in Engineer Technical Letter No. 1110–2–289 (U.S. Army COE, 1983c). The U.S. Maritime Administration operates the Computer Aided Operations Research Facility (CAORF) located at Kings Point, New York. Information pertaining to the facility can be found in various publications and papers, including proceedings of periodical symposia held at the CAORF facility and in minutes of deep-draft navigation channel design courses held at the Waterways Experiment Station (U.S. Army COE, 1983a and 1980).

Waves and drawdown generated by vessels can cause bank erosion, and propeller wash can cause scour of the channel bottom. This is discussed by Maynord (1984).

Turning Basin

A turning basin should be provided in interior channels to enable the vessel to reverse direction and leave the harbor or make a substantial change in direction. The basin is usually located at the upstream end of the channel, upstream of each port on a long channel, or at the entrance to a side channel. The size of the basin should be such that the vessel can turn under its own power by maneuvering within the basin or with tug assistance. Information for determining the size, shape, and depth of turning basins is shown in report EM-1110–2–1613 (U.S. Army Coe, 1983b).

A turning basin produces an increase in the channel cross-sectional area and changes in current will tend to increase the normal

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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rate of shoaling. Increase in shoaling in the basin could cause a reduction in the shoaling farther downstream and could reduce the area to be dredged; however, in systems with large sediment loads, the total dredging requirements will probably be increased by the turning basin due to the reduced velocity. The configuration of the basin may make it a very effective sediment trap.

Anchorages

Anchorages are provided in some ports or along the navigation channel for vessels awaiting berthing space, undergoing repairs, receiving supplies and crews, being inspected, and occasionally lightering off cargo (see U.S. Army COE, 1983b and 1965b for guidance).

Jetties

Jetties are structures that extend into the water to direct and confine river or tidal flow into a channel and prevent or reduce the shoaling of the channel by littoral material. Jetties located at the entrance to a bay or river also serve to protect the entrance channel from wave action and cross currents. In most cases two jetties are needed to keep littoral drift from entering the channel. They are normally aligned parallel with the selected channel alignment. Detailed design information for jetties can be obtained from U.S. Army COE (1986 and 1984). Hydraulic model tests are generally advisable for jetty layout to optimize alignment and lengths. Information pertaining to the capabilities and limitations of this type of model can be found in Coastal Hydraulic Models (U.S. Army COE, 1979).

Jetties can be constructed of rock (rubble mound), rubble with concrete armor units, sheet-pile cells, caissons and cribs using timber, steel or concrete. The type of jetty selected should be based on the imposed loads (waves, ice, vessel impact). They can be solid (impervious), semi-impervious, or with low sections (weir) to allow controlled deposition of littoral drift in semiprotected waters inside the jetty. Physical hydraulic models are generally useful in optimizing armor unit size and jetty height. A report by Hudson (1974) provides information and guidance in selecting the shape and size of concrete armor units for use in constructing rubble-mound structures that will be stable at a minimum cost.

The proper siting and spacing of jetties for improvement of a coastal inlet are important. Careful study must be given to sedimentation and maintenance costs. Effects of both net and gross longshore transport on methods of sand bypassing, size of impoundment area, and channel maintenance must be considered. Sand bypassing and/or channel dredging will usually be required, especially if the cross-sectional area required between the jetties is too large to be maintained by the currents associated with the tidal prism. Methods for sand bypassing are discussed in the Shore Protection Manual (U.S. Army COE, 1984).

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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A jetty (other than the weir type) interposes a total littoral barrier in that part of the littoral zone between the seaward end of the structure and the limit of wave uprush on the beach. Jetties are sometimes extended seaward to the contour position equivalent to the project depth of the channel. Accretion takes place updrift from the structures at a rate proportional to the longshore transport rate, and erosion takes place downdrift at about the same rate. The quantity of the accumulation depends on the length of the structure and the angle at which the resultant of the natural forces strikes the shore.

Breakwaters

Breakwaters are partial barriers at the entrances to the embayments, coves, or jettied channels in waters subject to severe wave action for the purpose of providing shelter from waves.

The principal criteria to be observed in the layout of breakwaters are adequate depths in the area to be protected from waves; adequate depths in the approaches to the entrance of the harbor; and an entrance that will minimize wave action within the harbor while providing adequate clearances for navigation. If the breakwater forms a harbor area, that area should not receive discharges of pollutants or natural water courses, since it is possible that the resultant water quality within the harbor will be unsatisfactory, and the suspended solids discharged by the stream can cause shoals due to the poor flushing characteristics of the enclosed area.

The orientation of the entrance should be such that approaches or departures to the entrance may follow a course generally at right angles to the direction of the more severe waves. The design of the entrance for the purpose of excluding or minimizing the propagation of waves into the harbor may be accomplished by procedures described in Committee on Tidal Hydraulics Report No. 3 (U.S. Army COE, 1965a). In many cases, model tests can be beneficial in optimizing entrance configurations.

Breakwaters interfere with shoreline processes and cause accumulation of beach material and erosion of beaches downdrift. Breakwaters attached to the land will accumulate sand on their updrift side. Detached (or offshore) breakwaters cause the accumulation of sand on the beach in their “wave shadow.” It will generally be necessary to plan some means for transferring the accumulated sand to the downdrift side to prevent shoaling of the harbor and to prevent erosion of the downdrift beaches. The Shore Protection Manual discusses means for accomplishing this end.

Breakwaters may be rubble mound, composite, concrete caisson, sheet-piling cell, crib, or mobile. In the coastal United States, breakwaters that have been built on the open coast are generally of rubble-mound construction. Occasionally, they are modified into a composite structure by using a concrete cap for stability. Precast concrete shapes such as dolosse, tetrapods, or tribars are also used for armor when sufficient size rock is not obtainable. Several types

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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of floating breakwaters have been designed and tested. Various types have been installed in the United States with varying degrees of success.

As with jetties, model studies are usually required to optimize the layout and stability of breakwaters. Literature referenced previously for design of jetties also will apply to breakwaters.

Salinity Barriers

Salinity barriers are structures that extend across the waterway for the purpose of excluding saline waters from upstream areas. They may be submerged weirs, locks, or a combination of the two. Information pertaining to these structures and their environmental aspects can be obtained from U.S. Army COE (1965b, 1983, and in preparation).

SEDIMENTATION MODELING

Modeling is widely employed to solve estuarine and coastal sedimentation problems. Sediment transport research and modeling efforts are presented in a paper written for a deep draft navigation channel course (U.S. Army COE, 1983a). In order to decide if modeling is an appropriate approach for a particular problem, we must understand the physical processes contributing to sedimentation, have a general idea of remedies that might be used to solve the problem, and know the strengths and weaknesses of methods available to study it. Sedimentation is dependent upon (1) the supply of depositable sediment and (2) flow conditions near the bed.

Four primary methods are available for studying sedimentation: field methods, analytical methods, physical modeling, and numerical modeling. Field methods include trial-and-error remedial measures, in which remedial works are constructed without benefit of corroborating study, full-scale experiments, and field measurements of physical parameters. They are usually expensive, but often indispensable.

Field measurements are necessary for understanding of physical processes and verification of models. Analytical methods employ simple mathematical expressions for which a closed form solution can be obtained. They are inexpensive, but cannot provide many details. Their usefulness declines with increasing complexity of geometry or increasing detail of results desired.

Physical scale models can be used to obtain reliable solutions to problems that often cannot be solved by any other method. Fixed-bed hydraulic models are extremely valuable tools in studying the effects of coastal construction projects on wave, tide, and current conditions. In recent years, the use of relatively small quantities of sediment tracer material in fixed-bed models has generally been accepted as a reliable and relatively inexpensive method of studying sediment transport due to wave and tidal action. Results of these tests are usually qualitative rather than quantitative. Physical hydraulic models of estuaries and coastal areas can reproduce tides and

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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other long waves, some aspects of short-period wind waves, longshore currents, freshwater flows, pollutant discharges, some aspects of sedimentation, and three-dimensional variations in currents, salinity, density, and pollutant concentrations. Applicability of model laws and choice of model scales are dependent on the problem of interest. Coastal Engineering Research Center Special Report No. 5 (U.S. Army COE, 1979) addresses this subject.

Numerical modeling employs special computational methods such as iteration and approximation to solve mathematical expressions that do not have closed-form solutions. A numerical model applies numerical analysis to solve mathematical expressions that describe physical phenomena. Numerical models are classified by the number of spatial dimensions over which variables are permitted to change, i.e., one-dimensional, two-dimensional, or three-dimensional. Numerical modeling provides much more detailed results than analytical methods and may be substantially more accurate, but it does so at the expense of time and money. Once a numerical model has been formulated and verified for a given area, it can quickly provide results for different conditions.

In practice, two methods of modeling may be used jointly, with each method applied to that portion of the problem for which it is best suited. For example, field data are usually used to define the most important processes and to verify a model that predicts hydrodynamic conditions in an estuary. Combining physical modeling and numerical modeling to provide results not possible any other way is termed “hydrid modeling.” Judicious selection of solution methods in a hybrid approach can greatly improve accuracy and detail of the results.

RESEARCH LABORATORIES

Throughout this paper I have discussed the use of modeling to assist in the design of various elements of a facility. The types and methods of modeling vary greatly, depending upon the element to be modeled. Many public, private, and university research institutions are capable of conducting the studies required. A Directory of Hydraulic Research Institutes and Laboratories is published by the International Association for Hydraulic Research (1980). A description of the facilities and capabilities of each of these institutions is shown in that publication.

SUMMARY

I have attempted to present a synopsis of factors that should be considered in designing a new facility and resources that are available to assist the designer. I have barely scratched the surface in most areas, hoping to whet the appetite of those with a real nead. Several of the subjects will be covered in much more detail in other papers in this symposium. Most of the reference manuals, reports, etc. are somewhat general in nature but contain many references for anyone desiring more detailed guidance.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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ACKNOWLEDGMENTS

Much of the information presented in this paper was obtained from publications of the Corps of Engineers. Permission was granted by the Chief of Engineers to publish this information.

REFERENCES

Bruun, Per. 1976. Port Engineering. Houston, Tex.: Gulf Publishing Co.


Hudson, R.Y. 1974. Concrete armor units for protection against wave attack. Miscellaneous Paper H-74–2. Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station.


International Association for Hydraulic Research. 1980. Directory of hydraulic research institutes and laboratories. Delft, The Netherlands.


Maynord, Stephen T. 1984. Riprap protection on navigable waterways. Technical Report HL-84–3. Vicksburg, Miss.: Waterways Experiment Station.


Turner, H.O. Jr. 1984. Dimensions for safe and efficient deep-draft navigation channels. Technical Report HL-84–10. Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station.


U.S. Army Corps of Engineers. 1986. Design of breakwaters and jetties. Engineer Manual 1110–22–2904. Office of the Chief of Engineers, Washington, D.C.

U.S. Army Corps of Engineers. 1984. Shore Protection Manual. Vicksburg, Miss.: Coastal Engineering Research Center, U.S. Army Engineer Waterways Experiment Station.

U.S. Army Corps of Engineers. 1983a. Deep draft navigation channel design course. Vicksburg, Miss.: Waterways Experiment Station.

U.S. Army Corps of Engineers. 1983b. Layout and design of deep-draft nagivation projects. EM 1110–2–1613. Office of the Chief of Engineers, Washington, D.C.

U.S. Army Corps of Engineers. 1983c. Ship and tow simulators. Engineer Technical Letter No. 1110–2–289. Office of Chief of Engineers, Washington, D.C.

U.S. Army Corps of Engineers. 1980. Deep-draft navigation channel design course. Vicksburg, Miss.: Waterways Experiment Station.

U.S. Army Corps of Engineers. 1979. Coastal hydraulic models. Special Report No. 5. Fort Belvoir, Vir.: Coastal Engineering Research Center.

U.S. Army Corps of Engineers. 1978. Effects of depth on dredging frequency. Technical Report H-78–5, Reports 1–3. Vicksburg, Miss.: Waterways Experiment Station.

U.S. Army Corps of Engineers. 1971. Report on the national shoreline study. Washington, D.C.

U.S. Army Corps of Engineers. 1965a. Evaluation of present state of knowledge of factors affecting tidal hydraulics and related phenomena. Report No. 3, Committee on Tidal Hydraulics, Vicksburg, Miss.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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U.S. Army Corps of Engineers. 1965b. Tidal Hydraulics. EM 1110–2–1607 Office of the Chief of Engineers, Washington, D.C.

U.S. Army Corps of Engineers. 1961a. General cargo vessels—trends and characteristics. Board of Engineers for Rivers and Harbors, Washington, D.C.

U.S. Army Corps of Engineers. 1961b. Study trends in petroleum supply requirements and tanker fleet characteristics. Washington, D.C.

U.S. Army Corps of Engineers. 1961c. Trends in dry bulk carriers. Washington, D.C.

U.S. Army Corps of Engineers. Continuing series of reports. Wave information studies of U.S. coastlines. Vicksburg, Miss.: Waterways Experiment Station.

U.S. Army Corps of Engineers. In preparation. Environmental Engineering for deep-draft navigation. EM 1110–2–1202. Office of the Chief of Engineers, Washington, D.C.

U.S. Department of Commerce. 1978b. Merchant fleet forecast of vessels in U.S.-foreign trade. Maritime Administration, Washington, D.C. Prepared by Temple, Barker and Sloane, Inc., Wellesley Hills, Mass.

U.S. Department of Commerce. 1978a. A statistical analysis of world’s merchant fleets. Maritime Administration, Washington, D.C.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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BUDGET OF SEDIMENTS FOR ESTUARINE HARBORS

Douglas L.Inman

Scott A.Jenkins

Center for Coastal Studies

Scripps Institution of Oceanography

Proper siting of a harbor is by far the most important consideration in determining its overall utility, cost of construction, and annual maintenance costs. Experience shows that annual maintenance cost for sediment removal is usually underestimated and frequently, with time, becomes the highest harbor cost. The common problem of underestimation of future dredging costs results from an inadequate assessment of the natural sedimentary regime and incorrect analysis of the effect of the harbor structures on the sediment budget. The purpose of this paper is to discuss the budget of sediment within the context of a natural sedimentary compartment referred to as an “estuarine cell.”

Before a realistic estimate can be made of the effect of new construction on the environment, it is first necessary to determine the important natural relationships among the physical driving forces and the sediment responses. Once these relationships are known, we are in a position to begin assessing the natural budget. It is a basic principle of sedimentary systems that they seek various states of short-and long-term equilibria. The effect of new construction on the equilibria can best be estimated when the natural states of equilibria are understood.

The concept of the budget of sediment, balanced within the physiographical limits of a sedimentation cell or compartment, has proven to be a very valuable aid in understanding and evaluating sediment management procedures. A sedimentation cell is a coastal compartment or physiographic unit that contains a complete cycle of sedimentation, including sources, transport paths, and sediment sinks. Within a cell the principle of the conservation of mass may be applied to the evaluation and interpretation of coastal and estuarine sedimentation. The procedure, sometimes referred to as the “budgets of sediment,” consists of assessing the sedimentary contributions (credits) and losses (debits) and equating these to the net gain or loss (balance) of sediment within a given coastal segment. The concept of the budget of sediment within a coastal compartment, called a “littoral cell” has led to considerable success in the analysis of the effects of coastal structures in causing accretion and erosion (Inman and Chamberlain, 1960; Inman and Frautschy, 1965; Inman and Brush, 1973; Inman et al., 1986). The intent here is to extend this concept to estuarine systems.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

ESTUARINE VERSUS LITTORAL CELLS

It is important to recognize that most estuarine harbors, by nature of their location, may have problems with littoral sedimentation along their entrance and access channels. Generally, estuarine harbors are situated on a bay or river separated from the sea by spits, barriers, tombolos, or headlands (Figure 1a). Examples are San Francisco, Mare Island, Kings Bay and most harbors on the east and gulf coasts of the United States. Littoral harbors are those that border the coast and debouch directly to the sea across the littoral zone. Examples are Los Angeles, Long Beach, and San Diego, California and Port Canaveral, Florida. The sediments and transport processes for estuarine and littoral environments are quite different. Mud and dynamics of fresh-/ saltwater interface are common to estuaries, while sand transported by

FIGURE 1 (a) Schematic diagram of estuarine processes. (b) Saline wedge and formation of sediment flocs.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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FIGURE 2 X-ray spectrogram of sediment samples taken at Mare Island, California. The percentage occurrence of a given mineral is proportional to the area under the intensity peak, referred to the basic background level indicated by the dashed line. SOURCE: Van Dorn et al., 1975.

waves and tidal currents are essential aspects of the littoral harbor. Harbors such as Kings Bay, Georgia are examples of estuarine harbors with severe littoral problems (Inman and Luftglass, 1979).

ESTUARINE SEDIMENTATION

Flocculation (coagulation) and eventual deposition of muds occurs when silt-laden fresh water from a river contacts salt water. The river water is usually lighter and rides over the salt water, their boundary forming a missing shear-layer where the dispersed suspended load of the river combines with salt water to form sediment aggregates termed “flocs.” This floc-generating frontogenesis zone may extend a number of miles seaward of the river mouth where the freshwater plume spreads over salt water (Gross et al., 1965; Garvine, 1975; Trefry et al., 1985). Alternatively, the interface may occur landward of the river mouth over the “saline wedge” that may extend along the bottom for many miles upstream (Keulegan, 1966; Krone, 1974).

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×

FIGURE 3 Cumulative frequency distribution of particle sizes in uniform dilutions of Mare Island sediment, as function of salinity. Particle sizes are referenced to the settling velocity of a quartz sphere of the indicated diameter. The sample treated with peptizer approximates the basic particle-size distribution before flocculations. SOURCE: Van dorn et al., 1975.

Once the flocs are in the bottom layer they may be carried upstream with the moving salt wedge. This recirculation of solids, consisting of downstream transport of wash load and upstream transport of flocs, is an important mechanism for estuarine sedimentation (Figure 1b).

COMPOSITION AND PHYSICAL PROPERTIES OF MUDS

The composition of the muds from the Sacramento-San Joaquin River systems are shown in the x-ray spectogram of mud from Mare Island Harbor in San Francisco Bay (Figure 2). This mud results from the salt wedge that travels upriver from San Francisco Bay. The clay compositions in percent by weight of montmorillonite, kaolinitechlorite, and illite are 25, 46 and 29 respectively. Reconstruction of the particle-size distribution of the original wash load from which the mud was formed was attempted by adding peptizer of sodium hexameta phosphate to deflocculate the material (Figure 3). The effect of increasing salinity on flocculation was determined for salinities of 0, 12, and 34 percent. The resulting cumulative frequency curves shows the systematic increase in median size of material through 2.4, 7, 9 and 12µ. The actual sizes of the flocs are much larger than shown because of the low density of the flocs (1.22 g/cm−3), which gives them a lower settling velocity than their size would warrant when

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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TABLE 1 Characteristics of Representative Bottom Sediments in Three Navy Harbors

SITE

SOLIDS % BY WT.

VOLATILES % BY WT.

BULK DENSITY gm/cm3

CLAY COMPOSITION % BY WEIGHT

MONTMORILLONITE

KAOLINITE+CHLORITE

ILLITE

Mare Island

97.5

2.5

1.22

25

46

29

Norfolk

88.0

12.0

1.21

21

48

31

Charleston

96.5

3.5

1.21

52

46

2

 

SOURCE: Van Dorn et al., 1977.

compared with the settling velocity for quartz spheres, which is used as the standard for “size” in Figure 3.

The flocs resulting from the nucleation of the smaller particles are larger and, although less dense than the small particles, they have greater fall velocities and settle to the bottom more readily. Since the flocs are loosely combined conglomerates of a number of particles, including water molecules, their physical and chemical properties are varied and change with time. They undergo compaction with a marked increase in viscosity. For example, freshly settled flocs of the material shown in Figures 2 and 3 could be moved (onset of particle motion) by fluid shear stresses of 1 dyne cm−2. After several hours, onset required a stress of 2.5 dynes cm−2, and as much as 3 to 5 dynes/cm2 after several days to weeks (Van Dorn et al., 1975; Jenkins et al., 1981).

The detailed mechanics of flocculation and the physical behavior of muds that form from the flocs are also dependent upon the clay minerals that form the flocs. These may differ widely from harbor to harbor as shown in Table 1 and discussed by Krone (1963). Although most muds contain two or more of the clay minerals, Griffin et al. (1968) show that the typical clay mineral is determined by source rock, climate, and weathering. For example, chlorite is characteristically a high-latitude clay that results from erosion of metamorphic rocks. The Saint Lawrence River system is a major source of chloritic clays. Montmorillonite is characteristically formed in volcanic regions, and rivers of the Pacific coast of North and South America usually have medium to high amounts. Kaolinite is formed by intense chemical weathering and is a typical mineral for rivers in low latitudes that drain high rainfall areas. Illite is a general term for a group of stable, micaceous (mostly muscovite) minerals characteristic of detrital sediment runoff from the continents. The clays’ presence and relative abundance are easily determined from an x-ray spectrogram as shown in Figure 2.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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SEDIMENT BUDGET FOR AN ESTUARINE CELL

The sediment budget for an estuarine cell may be approached in the same manner as that for a littoral cell. The principle difference is in the type of sediment and its mechanics of transport. As we have seen, the muds of estuaries behave in a very different manner from that of littoral sands. Further, the estuarine cell may also include sands, particularly in entrance and access channels where currents are stronger. Because of the many complex interactions in estuaries, it is sometimes necessary to divide the estuarine cell into a series of subcells in accordance with the relative importance of the littoral, lagoonal, and riverine portions of the estuary (Figure 1a). It should be understood that the estuarine cell may include elements of the other three (Pritchard, 1967a,b).

In detail, the procedure for estimating the sediment budget for an estuarine system can be handled like that previously described for a littoral cell (Bowen and Inman, 1966). That is, first identify all of the sediment sources, transport paths, and sinks. Then, use all available independent information to evaluate the rates associated with the sources, paths, and sinks. The result is an estimate of the budget of estuarine sediment. For an equilibrium system the three estimates of sources, paths, and sinks must all be equal. If the system is known to be in equilibrium, then balancing the budget suggests, but does not guarantee, that the budget is correct. If the estuary is not in equilibrium, the sources and sinks will not balance. Rather the net will equal the expected accretion or erosion. In this case the confidence of the result can only be assured by the most accurate possible determinations of sources, transport, and sink rates.

During early planning, the harbor engineer needs to have preliminary estimates of the sediment budget before all of the detailed studies and measurements have been completed. In this case it is necessary to apply principles of the controlling processes as an aid to obtaining preliminary estimates of transport rates. Examples of this procedure, which lead to first estimates of the sediment budget, are discussed below.

LITTORAL SEDIMENTATION

The littoral portion of the cell typically includes the shore zone where the principal transport mechanism is the longshore or littoral drift of sand driven by waves and wave—generated currents. This type of sediment transport is responsible for the shoaling of entrance channels and offshore access channels. It is usually the major sediment problem for littoral harbors such as Santa Barbara (Johnson, 1953) and Oceanside, California (Inman and Jenkins, 1983), and Port Canaveral, Florida (Van Dorn et al., 1977). At Saint Mary’s Inlet, the offshore access and entrance channel maintenance dredging for Kings Bay Harbor is estimated to be between 0.8 and 2.8 million m3/yr (Kings Bay Environmental Impact Review meeting, 1986).

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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The longshore transport rate of sand in the surf zone has been shown to be proportional to the energy flux or “stress flux” of the breaking waves. It can be estimated by summing the instantaneous transports obtained from the directional wave spectra (CERC, 1977; Inman et al., 1986).

The natural balance of sediment in the littoral portion of the cell requires that the supply of sediment equal the longshore transport of sediment, which in turn equals the sink of sediment:

(a)

(b)

(c)

supply=longshore transport=sink

For example, at Oceanside, California the supply of sediment (a) is from rivers, the longshore transport (b) is estimated using the stress-flux method, and the sink (c) is sediment lost down submarine canyons. Inman and Jenkins (1983) and Inman (1985) show that separate, independently derived estimates of these three quantities, in m3/yr, are:

(a)

(b)

(c)

213,000

194,000

200,000

It is apparent that these volumes of sediment are remarkably similar, and the budget of littoral sediment is essentially in long-term balance for natural conditions. This gives some assurance that the procedures and volumes are valid.

LAGOONAL/RIVERINE SEDIMENTATION

Lagoonal and riverine sedimentation are more complex as they include transport and deposition of sandy and muddy sediments. The processes include the important equilibrium between entrance channel cross-sectional areas and tidal prism; the mechanics of meandering tidal channels; saline wedge intrusion; salt marsh deposition; and for large lagoons and bays, littoral transport as well. In the long term, the geologic history of most lagoons is that of deposition and gradual disappearance. Although the continuing rise in sea level is retarding the rate of deposition, the demand for ever-increasing draft (about 20 cm/yr) far exceeds the eustatic sea level rise (about 20 cm/century).

The relationship between the cross-sectional areas of entrance channels and the tidal prism behind them (Jarrett, 1976) has proven to be a very useful guide for natural equilibrium conditions. The relation applies to sandy entrance channels and was originally developed by O’Brien (1931) and extended by Inman and Frautschy (1965). However, the relationship also applies approximately to the distributory channels within an estuarine system when the tidal prism is taken as the volume “upstream” from the channel section. For example, in a study of tidal relations along the coast of Vietnam, Inman and Harris (1966) found that natural channel areas near Chu Lai and Vung Tau (Dinh River) were in good agreement with estimates of

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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upstream tidal prisms. Estuarine harbor design usually leads to channel enlargement and deepening. Such channel enlargements have the potential for trapping sediment volumes equivalent to the enlarged section at intervals of only a few spring tidal cycles.

Preliminary studies for Kings Bay, Georgia (Inman and Luftglass, 1979) used the channel/tidal prism relationship for estimating maintenance dredging in the interior tidal channels, while the wave energy-flux method was used as an estimate for littoral fill in the entrance and approach channels. Together these procedures gave an annual maintenance dredging for 40-ft depth channels of 2–3 million yd3. For deeper draft Trident submarine maneuvering, the annual dredging was estimated to be much larger, almost 5 million yd3.

The saline wedge considerably complicates the budget of sediment by adding a mechanism that reverses the direction of transport from downstream to upstream (Figure 1b). Further, the concentration of sediment flocs in the saline wedge may be between 100 and 4000 g/liter, about 100 times greater than that in the waters above (Van Dorn et al., 1977; Jenkins et al., 1980).

In some European estuaries sediment may be introduced from the sea. However in most cases, the flocs in the saline wedge have their orgin in the wash load carried in the waters above the wedge. This is true even though the times of high deposition at any given locality in an estuary may lag by many days the times of high river runoff. The lag occurs because high discharges displace the saline wedge seaward and cause the load to be deposited farther downstream. High spring tides are important in re-establishing saline wedges that then transport flocs upstream. For example, deposition of mud from the flood of February 12–15, 1986, which occurred during a neap tide, did not begin at Mare Island until the following spring tide on February 25.

Thus, years with heavy deposition of mud correlate well with years of high river runoff when sediment is supplied to the estuaries (Van Dorn et al., 1977). Accordingly, the episodic climatic behavior that produces the 10-, 50- and 100-year floods becomes an important consideration in estimating the long-term budget of sediment in estuarine harbors.

REFERENCES

Bowen, A.J. and D.L.Inman. 1966. Budget of Littoral Sands in the vicinity of Point Arguello. Technical Memo 19. U.S. Army Corps of Engineers, Coastal Engineering Research Center. 41 pp.


CERC. 1977. Shore Protection Manual, Vols. I and II. U.S. Army Corps of Engineers, Coastal Engineering Research Center. 3rd edition.


Garvine, R.W. 1975. The distribution of salinity and temperature in the Connecticut River estuary. J. Geophys. Res. 80(9):1176–83.

Griffin, J.J., H.Windom, and E.D.Goldberg. 1968. The distribution of clay minerals in the World Ocean. Deep-Sea Research 15:433–459.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Gross, M.G., C.A.Barnes, and G.K.Reil. 1965. Radioactivity of the Columbia River effluent. Science 149(3688):1088–90.


Inman, D.L. 1985. Damming of rivers in California leads to beach erosion. Pp. 22–26 in Oceans ’85: Ocean Engineering and the Environment. Washington, D.C.: Marine Technological Society and IEEE. Vol. 1, 674 pp.

Inman, D.L. and B.M.Brush. 1973. The coastal challenge. Science 181(4094):20–32.

Inman, D.L. and T.K.Chamberlain. 1960. Littoral sand budget along the southern California coast. Pp. 245–246 in Volume of Abstracts, Report of the 21st International Geological Congress. Copenhagen, Denmark.

Inman, D.L. and J.D.Frautschy. 1965. Littoral process and the development of shorelines. Pp. 511–536 in Coastal Engineering. (Santa Barbara Specialty Conf.) New York: American Society of Civil Engineers. 1006 pp.

Inman, D.L., R.T.Guza, D.W.Skelly, and T.E.White. 1986. Southern California coastal processes data summary. Coast of California Storm and Tidal Waves Study, CCSTWS 86–1. U.S. Army Corps of Engineers, Los Angeles District. 572 pp.

Inman, D.L. and R.W.Harris. 1966. Investigation of sedimentation and dredging requirements, various locations, Republic of Vietnam. Prepared for U.S. Navy, OICC, Republic of Vietnam, under Contract by 79844 with Daniel, Mann, Johnson and Mendenhall, Saigon. 237 pp.

Inman, D.L. and S.A.Jenkins. 1983. San Malo Seawall. Letter report prepared for San Malo Beach Assn., Carlsbad, Calif. 3 pp.

Inman, D.L. and B.Luftglass. 1979. Summary report on nearshore processes affecting Kings Bay, Georgia. Special Report for Naval Facilities Engineering Command under Contract N00001476-C-0631. 10 pp.


Jenkins, S.A., D.L.Inman, and J.A.Bailard. 1980. Opening and maintaining tidal lagoons and estuaries. Proc. 17th Conf. Coastal Engineering, American Society of Civil Engineers 2:1528–1547.

Jenkins, S.A., D.L.Inman, and W.G.Van Dorn. 1981. The evaluation of sediment management procedures: Phase IV–VI, final report, 1978–1980. Scripps Institution of Oceanography Reference Series 81–27. 78 pp.

Johnson, J.W. 1953. Sand transport by littoral currents. Proceedings 5th Hydraulics Conf., Bulletin 34, Studies Engineering. State University of Iowa. Pp. 89–109.


Keulegan, G.H. 1966. The mechanism of an arrested saline wedge. Pp. 546–574 in Estuary and Coastline Hydrodynamics, A.T.Ippen, ed. New York: McGraw-Hill. 744 pp.

Krone, R.B. 1963. A study of rheological properties of estuarial sediments. Hydraulic Engineering Laboratory, University of California, Berkeley.

Krone, R.B. 1974. Anticipated effects of water diversions on the San Francisco Bay System. University of California, Berkeley. Preprint. 30 pp.


O’Brien, M.P. 1931. Tidal prisms related to entrance areas. Civil Engineering 1(8):738–739.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Pritchard, W.D. 1967a. What is an estuary: Physical viewpoint. Pp. 3–5 in Estuaries, G.H.Lauff, ed. Washington, D.C.: AAAS. Publ. 83.

Pritchard, W.D. 1967b. Observations of circulation in coastal plain estuaries. Pp. 37–44 in Estuaries, G.H.Lauff, ed. Washington, D.C.: AAAS. Publ. 83.


Trefry, J.H., S.Metz, and R.P.Trocine. 1985. A decline in load transport by the Mississippi River. Science 230:439–441.


Van Dorn, W.G., D.L.Inman, and R.W.Harris. 1975. The evaluation of sediment management procedures. Phase I, final report, 1974–1975. Scripps Institution of Oceanography Reference Series 75–32, 82 pp.

Van Dorn, W.G., D.L.Inman, R.W.Harris, and S.S.McElmury. 1977. The evaluation of sediment management procedures. Phase II, final report, 1975–1976. Scripps Institution of Oceanography Reference Series 77–10, 107 pp.

Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 327
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 328
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 329
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 330
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Page 331
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Page 332
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Page 333
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Page 334
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 335
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
×
Page 336
Suggested Citation:"Session E: New Facility Design Considerations." National Research Council. 1987. Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries: Report and Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1023.
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Page 337
Next: Appendix A: Committee Membership and Expertise »
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