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APPENDIX B SELECTION FROM ENGINEER lo* CHANNEL AND HARBOR DESIGN .~. I:~.~EL ~ IDTH, DEPTH, .\LIG~. IE1~T, AND ORIENTATION. a. Based on na~i~,atio requirements. General. Channel width is premised on the beam and steering characteristics of the design vessels, the traffic density and the characteristics of other vessels encountered in the channel, the characteristics of the waves likely to be experienced in the several reaches, as well as the characteristics of the banks. Channel depth is determined by the in-motion draft of the design vessel, the density of the water, wave characteristics, the tidal character- istics, the characteristics of the bottom, and the economics of greater depth as a factor in reducing power requirements for the propulsion of the design vessel. Channel alignment and orientation from the viewpoint of navigation are determined on the basis of the length of the design Vessel, the characteristics of the Raves in the several reaches, and the strength and direction of the currents. It will be noted that the characteristics of the design vessel enter into every aspect of channel design. The In vessel. It is well known that there are nationwide and worldwide trends towards larger general cargo and bulk-carrying vessels. Similar trends may or may not be applicable to traffic on the ``raterway under consideration, due to peculiarities of the commerce that is expected. For example, if the existing depths in the other ports of call involved in the prospective commerce are not likely to be increased, then it is probable that the characteristics of the vessels will remain constant throughout the economic life of the project. The selection of the design vessel will be made realistically, as it would be wasteful to provide a channel of greater depth and width, or a better alignment, than is necessary to accommodate the vessels likely to use it. The initial step should consist of an examination of general trends in the classes of vessels involved, then determinations may be made as to their applicability. Data on general trends may be seen in "General Cargo Vessels - Trends and Characteristics," ~6 "Study of Trends in Petroleum Supply and Re- quirements and Tanker Fleets and Characteristics," ,: and "Trends in Dry Bulk Carriers." ~8 Channel depth. The design depth of the channel will be premised upon the drafts of the design vessel while in motion, including the effect of squat, rolling, and pitching; plus a nominal clearance of 2 or more feet; plus an allowance for frequent low tides that are below mean lo`v water, when vessel delay is uneconomical, or minus an allowance for some stage above mean low water when the resulting delay of vessels is not uneconomic. Consideration will be Wren to the provision of greater depths than those required for safe navigation, as determined by the foregoing considerations, when it can be shown that the reduced power required to propel the vessel at a maximum safe speed at the greater depths produces savings commensurate with the costs of providing the greater depths. T; he draft of ~ vessel, An. m~~ m; dstermi~d by the Ratio- draIt of- the vessel in water of the density of that which will be in the channel to be designed; the speed of the vessel relative to water, in the channel to be designed; the distance between the channel bottom and the vessel keel; the characteristics of the vessel; the characteristics of the channel, i.e., whether it is located in open waters or is fully restricted; the likelihood that the vessel will meet and pass other large veneer; and the amount of the roll and pitch of the vessel due to wave action. The draft of the vessel while transiting the channel to be designed may vary from reach to reach depending on the safe speeds for the various reaches, water speed variations, water density variations, and variations of the geometry of the waterway and the navigation channel. *U . S . Army Corps of Engineers ~ 1965 ), Tidal Hydraulics, Engineer Manual EM 1110-2-1607 (Washington, D.C.: U. S . Army Corps of Engineers), pp. 7-12. B-1

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B-2 The static draft of the design vessel will not necessarily be assumed to be that in its fully loaded condition. In marry instances, it has been found that the draft on both arrivals and departures is less than that of the fully loaded ship. On the other hand, it may be found that the as-Ioaded condition results in a greater draft aft than forward, or vice versa. The static drafts taken for channel design purposes ~~] be those considered to be normal for the particular operations of the design tresses in the channel under consideration. The static draft of a ship is usually stated with reference to its flotation in "summer salt water." In passing from sea water of normal ocean salinity to fresh water, a ship having a static draft of 35 feet in sea water at lS degrees centigrade (density 1.026) will have a static draft of 35.9 feet in fresh water at the same temperature. If the channel to be designed traverses a waterway having brackish or fresh water, care wait be taken to assure that the static draft to be used in the design of the channel is commensurate with the normal density of the water in the proposed channel. In some waterways, the density may vary from mouth to head of tide. The increased draft of a vessel while under way, or "squat," as it is more commonly known, is a variable depending on man, factors including the characteristics of the vessel itself. It must be evaluated based on conditions likely to be experienced in the operations proposed in the channel to be designed. It sometimes happens that the owners of the design vessel have data on its squat under various conditions, but it is likely that dependence wild have to be placed on estimates. Chapter X of Reference 4 provides information that will facilitate making estimates of the squat, and References 19, 20, and 21 go into the theory of the phenomenon. A squat of about 3 feet is likely to be the maximum. The speed at which the design vessel will be operated in the proposed channel should be selected very carefully. It will normally be less than the full speed possible in the open ocean, as both squat and vessel-generated was es become excessive at high speeds in a relatively shallow and narrow waterway. It is unlikely that it will be economic to design a channel of such depth and width as to permit full speed of the design vessel, and such speed in most waterways would not be permitted because of the hazards. Large waves may damage shore establishments and moored vessels, and they could be very hazardous for small craft. The rolling and pitching of vessels due to ware action causes parts of the vessel to descend to depths greater than that due to squat alone. For example, a 5-degree roll of a vessel with a 100-foot beam would increase the draft of the vessel about 3.5 feet. The increase in draft due to- pitching cod be e~ greaten;< dependiTrg our the hedge and length of the waves experienced, and the length of the vessel. Consultation with masters of ships similar to the design vessel may yield reliable information on the amount of roll and pitch under conditions likely to be experienced' in the channel under design. This subject has been given considerable study; see "On the Motion of Floating Bodies," or "The Motion of a Ship, as a Floating Rigid Body."~3 Determination of minima] channel depths will be premised on the drafts of the design vessel under normal operating conditions in the channel. They will include allow- ances for sinkage due to fresh or brackish mater, squat, rolling, and pitching. In addition, an atIowa;ncE of :3 beet wills narmathr be add to tite draft of t}m vessel -while in Minoan, including increments due to rolling and pitching. As a safety precaution, this clearance between the-keel and the bottom will be increased to 3 or more feet if the bottom is rock.

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s-3 Examples of the computations that should be made for several reaches of a hypothetical channel follow: Reach 1. Entrance channel, full speed permitted, severe wave action possible, sea water of normal ocean salinity, sandy bottom. Design vessel static draft 29.0 feet (Summer sea water) Squat for economic speed 3.0 feet Rollins: and pitching 6.0 feet feet - Clearance Required channel depth ; 40.0 feet Reach 2. Intermediate reach, shoreline undeveloped, traffic density low, full speed per- mitted, moderate wave action, water of half-normal sea water salinity, sandy bottom. Design vessel static draft 29.0 feet (Summer sea water) Sinkage due to brackish water . _ ~ 0.o foot Squat for economic speed 3.0 feet Rolling and pitching 2.5 feet Clearance . ~ ~ 2.0 feet Required channel depth 37.0 feet Reach 3. Terminal section, shoreline highly developed, traffic density great, reduced speed required, no wave action, fresh water, rock bottom. Design vessel static draft ~ ~ 29.0 feet (Summer sea water) Sinlcage due to fresh water . _ 1.0 foot Squat for safe and economic speed . ~ ~ 2.0 feet Rolling and pitching 0.0 foot Clearance . _.~ 3.0 feet Required channel depth 35.0 feet The depths thus determined may be referred to mean low water (or mean lower low water on the Pacific coast of the United States) or above or below these datums. In cases where design vessel traffic will be low, it may be in order to provide a channel of the design depth when the tide is, say, at half tide level. Where the number of transits of the design vessel and other vessels of comparable draft will be large, and the frequency of tides below mew or mllw also is large, consideration will be given to the provision of the design depth when the tide is at some stage below mew or mIlw. In all cases. the basis of the decision will be an economic analysis involving the delays that will be experienced by vessels and the saving in dredging costs. In making such an analysis, it must be kept in mind that a vessel can ordinarily carry a given tidal stage throughout mfl~.of~ i=. iour.ney upstream in the majority of estuaries of the United States, but this cannot be done during downstream passages in the longer estuaries. In waterways where the selected plane of reference for providing the design depths varies significantly in absolute elevation from reach to reach, the waterway should be sectionalized and a separate datum used for each section rather than a single datum for the entire waterway. In some cases, local mean low water is as much an a foot higher in the upstream reaches as compared with the lower sections. If the design depth is excavated relative to a common datum throughout such a waterway, the resulting depth would be ~ foot greater in the upper section than would exist in the lower section. This useless increment of depth cou~ be ve" Conk.

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s-4 Channel with. The width of the channel is measured at the bottom of the side slopes, i.e., at the design depth. The design width depends on whether the design vessel is likely to meet and pass other vessels that must stay in the main navigation channel, whether the channel is in a wide waterway, the characteristics of the bed and banks, the design depth, the existence of yawing forces such as currents and waves at angles to the channel, and the characteristics of the pressers and their operators. There is no formula for evaluating all of these factors and their complicated interrelationships, but Reference 4 should be consulted for guidance. In addition, study of other waterways having commerce similar to that expected in the channel being designed may be helpful. However, it should not be assumed that the proper width is necessarily that of an accident-free channel in another waterway u ith similar characteristics; it may be that that channel is uneconomically wide. Channel alignment. Knowledge pertaining to this area of channel designing is presently inadequate. Experience has shown that it is more difficult to navigate a vessel on a curve than in a tangent reach; that the difficulty increases as the radius of curvature decreases, also as the size of the deflection angle increases; that reverse curves are undesirable; and that sighting distances in the curve must be adequate for the safe passing of other vessels in the curve. It is thought that the radius of curvature should be related to the lengths of the larger vessels expected to use the waterway, but there is little experi- mental or theoretical data available for determinations of limiting values for the radius of curvature, the deflection angle, the tangent length between curves, and the sighting distance. In Reference 19, it will be found that conclusions were reached, based on judgment alone, that the minimum radius of the proposed sea-level Panama Canal should be 12,500 feet, the maximum deflection angle 26 degrees, the minimum tangent length 4.2 miles, and the minimum sighting distance 1.52 miles. Channel widening at turns should be accom- plished in accordance with the criteria presented in chapter X of Reference 4. It is noteworthy, that the channel alignments of important existing projects in the United States are often inferior to those proposed by the Panama Canal engineers. In brief, if curves must be used, the best practice will be to lay out the channel with the maxima radii and the minima deflection angles, and the maximum tangent distances that the physical conditions permit, without incurring excessive first or annual costs. A radius of less than 5000 feet appears undesirable for major commercial waterways for vessels over 500 feet in length. Ckanne' onentat?on. The orientation of the channel within the waterway depends largely on the orientation of the natural deep reaches. In general, these follow the direction of the currents, which is desirable from the viewpoint of navigators. If the current is at err angler to the Mean - ; steerage wr}! be Somers - t more d~f5~. The? orientation of entrance channels should be such as to head them into the direction of storm waves, if practicable. b. Channel width, depth, alignment, and orientation based on case of maintenance. General. The design of a channel for ease of maintenance must of course go hand in hand with design in the interest of navigation. It is rare that the channel which is most favorable to navigation is also the one that requires the least maintenance, and it is there- fore sometimes necessary to consider a channel that is less than the optimum, from the viewpoint of nas~igat~on, to keep annual cow ok Tnaintena~ within retainable boun~- For example, channels that do not follow the natural thalweg usually are more subject to shoaling than those that are located generally along its course, but as the thalu~eg is often

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B-S somewhat sinuous, it is more difficult to navigate than a channel with longer tangents. Coni- mercial or recreational needs often indicate the desirability of extending a channel into the upper limits of the estuary, or into coves, tributary streams, or interior basins, but it often happens that such channels shoe] much more rapidly than the existing downstream channel. Chantte! depth. The construction of a channel that is appreciably deeper than the natural depths along the course of the thalweg, or the deepening of an existing channel, may engender a difficult maintenance problem. After the depth required for safe navigation of the design vessel has been determined, it may be found that such a channel cannot be justi- fied. Consideration will then be given to channels of lesser depths that would be suitable for the design tresses u hen advantage is taken of the tide. The governing considerations frequently are the natural depths of the thalweg, the depths beyond the limits of the pro- posed channel, the magnitudes of the changes in the cross sections of the estuary if the pro- posed channel is constructed, and the kinds of material available in the waterway beyond the limits of the channel for transport into the channel by density flows and by the tidal currents. For example, the shoaling rate of a channel of a Even width and 40-foot depth located in a relatively very wide waterway may not be appreciably greater than that of a channel of the same plinth but 37 feet deep. The resulting cross sectional areas created by the turo channels may not be significantly different. On the other hand, if the range of tide is large it may be possible to serve the design vessel reasonably well with a channel depth of 30 feet instead of the optimum of 40 feet. In this case, the resulting cross sectional area may be sufficiently closer to the natural or pre-improvement cross sectional area to effect a considerable saving of maintenance costs. Similarly, if the natural depths along the thalweg fire 10 feet and a channel of 40-foot depth is the optimum, it is unlikely that there would be much difference in maintenance costs between a 40- and a 37-foot channel, other factors being equal, but the difference could be appreciably between 40- and 30-foot channels. Channel depth sometimes has a profound effect on the distribution of shoaling as well as the rate of shoaling. For example, a channel 40 feet in depth may cause the bulk of the shoaling to occur in a place where there are no disposal areas, while a channel depth of 35 feet may shift the location of the heaviest shoaling to a location downstream, where disposal areas are plentiful, or the effects of the two depths could be reversed from those discussed here. Distance of the disposal area from the bulk of the shoaling is, of course, a factor in the cost of maintenance. Channel depth helps determine the location where the upstream predominance of bottom currents over downstream bottom currents occurs. References and 15 should be consulted for additional information on this matter. Channel width. While channel width and channel depth are factors of equal signifi- cance insofar as cross sectional area is concerned, it appears that inadequate depths are much more hazardous than inadequate widths, and they cause greater delay to vessels. On the other liand, a choice between Lie provision of a channel of width adequate ~ permit two-way traffic and inadequate depths at low tide, as compared with a channel suitable for one-way traffic of design vessels and of adequate depth even at low tide, must take cognizance of the possibility that the greater depth may cause a shift in the location of the bulk of the shoaling. Channel alignment. Channels should be located as closely to the alignment of the thalweg as is practicable, keeping in mind that the larger vessels cannot navigate the sharp bends that sometimes are characteristic of the alignment of the thalweg. In cases where there are two deep areas of approximately equal depth, the relative merits of each should be considered before selecting one of them for improvement. When it is found that the align- ment of ~ c~} Iocated on the ikalwegr would be the 31DWOS ~;~ me;; V~~] reasonably, consideration will be given to the use of training works having for their pur-

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B-6 pose the shifting of the current, and with it the location of the natural thalueg, more nearly to conform with the necessary alignment of the channel for navigation. Local interests may desire to have the channel located adjacent to the inside bank of the waterway in order to permit development of the frontage for docking facilities. This is fundamentally unsound; both the channel and the water areas adjacent to the docks will shoal rapidly and there is generally no satisfactory remedy. Entrance or approach channels to tributary streams, harbor areas in coves or in canals, and docks located on the inside of curves, must be aligned across the currents of the main waterway. If the natural depths along the course of such channels are inadequate to serve the navigation for which the facility is designed, it must be expected that the dredged channel will be subject to rapid shoaling. As it is unlikely that a practicable remedy for this shoaling can be found, the channel may as well be aligned to follow the shortest path to the facility, consistent with the needs of navigation. c. Channel width, depth, alignment, and orientation based on effect of water quality. Changes in the geometry of tidal waterways caused by deepening, widening, or extending channels in the interest of navigation may have an important and far-reaching effect on the salinity of the water and on the flushing and dispersal characteristics of the regimen. These effects may cause pollution of water that formerly was used for domestic and indus- tria] purposes, and thereby cause a severe economic loss. The change in the salinity may af- fect the hydraulics of the waterway in a manner that will cause shoaling. These possibilities should be evaluated very carefully in formulating conclusions as to the advisability of modifying a channel. References 4, 8, and 15 should be consulted for guidance in setting up the study. In the event it is found that a channel modification of the nature most desirable for navigation will have adverse effects on the quality of the water and hence on its value as a source of water supply, further study may consider possible reduc- tions of the dimensions and/or extent of the channel, barriers to exclude salinity', upland reservoirs to enhance low fresh water flows, or the provision of an alternative source of water supply to replace the tidal waterway as a source of water supply.