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1 Introduction Coastlines border 30 of our 50 states and Guam, Puerto Rico, and the Virgin Islands. Approximately 85 percent of the nation's population resides in these coastal states and possessions, with nearly 53 percent of the total U.S. population now living within 50 miles of a coast.: Concurrent with this growing population is an increasing strain on econorn~c, legislative, and political decision-making processes that attempt to maintain a balance between population pressures and en- ~rironmental equilibrium. As an example, harbors are essential for baking our nation's land transportation systems to vital overseas trade routes. But few harbors, if any, have been built without a significant effect on adjacent shoreline configuration. The appropri- ate design, construction, and maintenance of harbors is still a major ~ ~ Issue In coastal engineering. Harbors are only one example of the growing need for coastal and ocean engineering research. Numerous other issues must be addressed before the nation can cope with the increasing pressures iStatistical Abstract of the United States, 1984. The population of all coastal counties and municipalities in 1984 (123 million persons) was 52.6 percent of the total U.S. population (235 million persons). A county is designated as being acoastal" if the geographic center of the county is 50 miles or less from the ocean or the Great Lakes. 7

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8 being focused on its coasts. ~ a presentation made in 1976 at the Specialty Conference on Dredging and its Environmental [~sues in Mobile, Alabama, Mr. W. H. Sanderson, Chief of Construction Operations Division 1 (Wilmington District), U.S. Army Corps of Engineers noted that, while dredging ~ one of the oldest forms of engineering works, the modern-day engineer faces practically the same ocean inlet and navigation problems that confronted settlers in colonial times in their efforts to gain and keep access to the open sea. The long-standing problem of how to stabilize and maintain our harbor entrances and assure the use of navigational waterways continues to challenge coastal engineering. The size of the task is ev- idenced by the fact that maintenance dredging now costs the nation over half a million doDars annually. However, with the cost-sharing provisions of the Water Resources Development Act of 1986 (P.~. 9~662), related large-scale combined Corps of Engineers and lo- cal government research ~ searching for ways to reduce the cost of dredging while enhancing shore protection. One example of such research, which reflects the close relationship between dredging tech- nology and coastal engineering, is the feeder berm concept. The feeder berm will take beach-quality material excavated from harbor entrances or offshore channeb and place it at selected sites just off the beach where storm wave action would gradually move the material in the downdrift direction. This sediment movement would increase the volume of material available in the littoral zone, resulting in a more gentle underwater slope or gradient, and contribute to reducing shoreline erosion rates. The success of this innovative approach must be gauged largely by the ability of the engineer and researcher to measure coastal changes. The drive to live and play near the water has led to urbaniza- tion, which has presented significant challenges for coastal engineers. Structures have been built on the beaches, in the dunes, on the cliffs, and even over the water. Developers have flattened dunes, built in natural cuts, and sliced through natural barriers. Canals have been carved and dredged in wetlands and lowlands, sometimes with little regard to circulation, potential erosion, and sediment disposal. In- deed, our society has often disregarded the forces of the sea and the natural phenomena associated with them. Now we must cope with the resulting environmental damage. To repair this damage and prevent further destruction, coastal

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9 engineers require better and more complete data on coastal pros ceases. Additionally, theoretical and modeling studies, requiring spe- cific data sets, are needed to develop a better understanding of coastal processes and their effects on beaches, harbors, and structures. These data needs require that better coastal engineering measurement gym tems be developed and deployed. According to the jointly sponsored National Science Foundation and Office of Naval Research report titled "Natural Hazards and Research Needs in Coastal and Ocean Engineering" (NSF, 1984), Each year in the United States, natural and man-made hazards in our coastal and ocean environs cost many lives and sometimes billions of dollars in loss of property and commerce. These losses can be reduced through engineering research which produces better understanding of the hazards and better ways of dealing with the physical and economic results of severe events. Clearly instrumentation and measurement systems are required to provide the data and modem necessary to the attainment of this "better understanding." Reports and articles such as Shrinking Shores," in Time, August 10, 1987, or ~Bayside Owners Fight Erosion, Inevitable Tide," in The Washington Post, October 3, 1987, highlight the dilemma of coastal residents. The Time article indicates that development and poor planning have contributed to several coastal problems and cites examples of beach erosion undermining fashionable homes on Long ~land, bluffs dropping out from under homes on the California coast, and beaches receding in the Carolinas at rates from a few feet to as many as 100 feet per year. Beach recession is further exacerbated by the episodic onslaught of tropical storms and damaging hurricanes. Adding to these conditions is the rise in relative sea level over the past 100 years. Seldom can an accurate econorn~c value be placed on the damage caused by winter storms on areas exposed to high-energy wave forces. The January 1988 storm that hit the Southern California coast was one exception; the coastal damage wan estimated to cost $28 million. Equally important to the evaluation of the storm's effect was the ability to quantify the characteristics of that stormto measure wave parameters and document beach erosion and benthic profile changes. This knowledge can be attributed partly to the in-place coastal wave monitoring program for the San Diego Coastal Region of the U.S. Army Corps of Engineers (COE, 1989~. This system costs

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10 less than $500,000 to install; annual operating expenses are about $100,000. We are hearing cries for environmental protection, for deter- m~nation of cause, and for solutions. Calm for design skills in the construction of jetties, groins, seawalis, and other protective struc- tures to hold receding beaches are commonplace. Some actions being taken are beach restoration and sand bypassing by using weirs in jet- ties and using small dredges in channel areas to return sand to beach areas. PREVIOUS RELEVANT REPORTS AND STUDIES The growing awareness of coastal engineering problems has in the past decade resulted in a number of studies directed at spe- cialized and general needs for future research and development. A comprehensive conference on ocean current measurements was spon- sored by the Institute of Electrical and Electronics Engineers (IEEE, 1982~. Recommendations from this conference indicated the need for hardware and software standards and a government-sponsored cen- tral testing and calibration facility. The National Research Council (NRC) Symposium and Workshop on Wave Measurement Technol- ogy (NRC, 1982) emphasized the need for long-term wave-recording systems to establish reliable wave statistics for engineering design. Additional NRC conferences have been held, including one on remote sensing of the ocean surface (NRC, 1986) and another on directional wave spectrum applications (NRC, 1982~. The Institution of Civil Engineers (ICE, 1985) in England convened a pane! in 1984 to assess the research and development requirements in coastal engineering. This pane} concluded that the most common design requirement for coastal engineers is the need for good wave information, particularly directional information. Adequate knowledge of waves in deep water is necessary to forecast the impact of waves in shallow water. The National Science Foundation (NSF) sponsored a workshop called "Shallow-Water Ocean Engineering Research: Research Needs and Facilities" in 1983. The NSF, in cooperation with the Once of Naval Research (ONR), also sponsored an ad hoc Committee on Nat- ural Hazards and Research Needs in Coastal and Ocean Engineering, in 1984 (NSF, 1984~. Both groups identified specific research needs that should be addressed. The Shallow-Water Ocean Engineering Research workshop group

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11 identified needs in eight pr~rnary areas of research in coastal engineer- ing. Within five of these eight research areas specific needs were iden- tified for coastal instrumentation and measurement systems. These needs included the flowing: AREA breaking waves. wave attenuation... coastal protection..... NEED . instrumentation to measure velocity fields in aerated water; .... instrumentation for measurement of bot- tom shear stress; . measurement of wave-impact forces on structures, measurement of fluid flow in and around protection structures, more wave data in vicinity of coastal struc- tures, . more monitoring of submerged and de- tached breakwaters; sediment transport- instrumentation to withstand severe storm waves for high-energy-surf-zone measure meet; diffusion and mixing. measurement in multilayer and reversing flow, . measurement of wind-induced shear and wave formation, . measurement of velocity gradients in the horizontal and vertical. The Shallow-Water Ocean Engineering Research workshop group also stressed physical and mathematical modeling of coastal processes as a critical area for development. The ad hoc Committee on Natural Hazards and Research Needs in Coastal and Ocean Engineering identified needs in five areas of field-related research. Within each of these five areas there were either specified or implied needs for coastal measurement systems. Following is a summary of these needs: AREA hazard assessment.... NEED . information about physical and statistical anatomy of natural hazards such as winter storms, hurricanes, and tsunamis,

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12 long-term studies - long-term measurement of wind speeds, wave heights, and recurrence intervab, instruments and techniques for measure ment of physical phenomena in the surf zone and nearshore during high-energy events; long-term studies (years) to identify im- portant slowly varying phenomena such as gradual changes in ocean sea level and shift- ing of geological features; post-event surveys . rapid response to measure post-storm dam- age to obtain data otherwise lost within a few weeks of the event prototype . accurate measurements of the response measurements (stresses, motions) of seaward, breakwaters, moored platforms, piers, pipeline ballast, and other structures. Certain of the aforementioned research measurement needs have been investigated in recent cooperative field studies. The Nearshore Sediment Transport Study (Seymour, in press, 1989) provided two extensive sets of data on nearshore currents and surf-zone waves, bottom response, and sedunent transport. The Canadian Coastal Sediment Study (NRC-Canada, 1986) was a research study designed specifically to investigate sand transport on beaches. The Nearshore Environment Research Center (Horikawa, 1988) project in Japan was a multi-institution study that incorporated field measurements In an attempt to develop numerical models for predicting beach evolution caused by coastal structures. DUCK 'S2, 'S5, and 'S6 (SUPER- DUCK) were three multi-institution field experunents conducted at the Coastal Engineering Research Center (CERC) facility in Duck, North Carolina. DUCK 'B2 focused on storm-induced nearshore pro- cesses related primarily to morphologic response (changes in shape at the seabed). DUCK '85 was a more broadly based study to enhance fundamental understanding of nearshore processes under both low- and high-energy wave conditions. Finally, SUPERDUCK was con- ducted as an improved and expanded version of DUCK '85, intended to provide high quality, comprehensive sets of data to evaluate and improve numerical and analytical models of nearshore processes. Cornrnon to all of these field studies was the use and testing of state-of-the-at measurement systems and techniques. Various findings emanating from these field studies provide useful input to the assessment of measurement needs undertaken in this report.

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13 Specifically, there was an overald concern for better ways of measuring bed-Ioad sediment transport, as well as for continuous measurement of suspended sediments In the vertical water column. Concern was expressed for improved methodology for making high-wave-energy surf-zone measurements on bathymetric, sedimentologic, and fluid dynamic parameters. All of the preceding studies and committee recommendations focus attention on the urgent need for a well-coordinated national effort to develop costar measurement systems. It is the intent of this report to integrate previous findings with a comprehensive evaluation of existing needs and capabilities in order to provide a specific set of conclusions and recommendations to the research and development con~nunity. It is hoped these reconunendations and conclusions will spur expanded efforts to develop measurement systems for coastal engmeerlng. COASTAL ENGINEERING AND PROCESSES The term Coastal engineering," as discussed in this report, has been limited to the inner continental shelf and nearshore zone, rang- ing from water depths that are just within the zone of wave shoaling to the shoreline, where the energy from these waves is dissipated. The report also addresses backshore engineering considerations where damage from storm surge often occurs. By restricting considers tion to these zones, several critical coastal environments are not addressed, including estuaries and lagoons and the m-to-outer con- t~nental shelf. Recent NRC reports have addressed some aspects of estuarine-lagoonal engineering; the mid-to-outer continental shelf presents engineering design problems somewhat different from those of the inner shelf-nearshore zone and ~ beyond the scope of this re- port. Successful engineering within this inner coastal zone is essential if people are to live there in harmony with the environment. MEASUREMENT COMPLEXITIES Diversity of Conditions Processes in the open ocean show a broad uniformity over large (kilometers and more) space scales. The coastal zone, on the other hand, exhibits nonuniformly in the cross-shore direction because of wave shoaling, in the longshore direction because of changes in shoreline orientation and shoreline structures, and in every direction

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14 because of distributed shoals, bars, and irregular bottom bathymetry. The diversity of scales makes tints environment unique, as does the overall high-energy characteristic of the coastal region. Coastal en- g~neering measurement systems for the inner continental shelf and nearshore zone must be designed to accommodate the diverse spacer time scales of processes and conditions that interact within this shallow-water column. Measurement systems must be designed to characterize the broad, basin-wide atmospheric pressure systems driving waves toward the coast; other measurement systems must resolver the much smaller, beach-scale processesprediction of which is the ultunate goal of much of coastal engineering. Conditions in the coastal wave zone are exceedingly "noisy to measure"; that is, the signal-t~noise ratio there ~ often very low. Measurement system must be fast enough to measure processes occurring within the few seconds of a single breaking wave while also acquiring accurate data over much longer tune scales, including climate-change-induced occurrences like rely tive sea level change. Most of these measurement systems must sur- Yive the large forces accompanying breaking waves, strong tidal and nontida] currents, and high levels of sediment concentration within the water column. The combination of shallow water, high sedi- ment mobility, eroding shorelines, and poor predictability not to mention constantly changing wave conditions, currents, and bottom fortune (small-scale topography features)all make this environment a difficult one to monitor. W~n~, Waves, Currents, and Tides The important driving forces in the coastal zone include winds, waves, currents, and tides. While local winds generate local waves and create higher water levels during storms, pressure systems thou- sands of kilometers from the coast create winds that ultimately may have a severe impact on the shoreline. Waves are perhaps the outstanding characteristic of the inner shelf-nearshore zone. Waves change from their relatively predictable dee~water form once they encounter the shallow water of the shelf. 2Resolution in measuring systems refers to the minimum unit or quantity that can be discerned. For example, on a ruler, one millimeter might represent the resolution limit. At the other extreme, atmospheric pressure gauges are not typically close enough together to resolve compact storms like tornados.

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15 Complexities of bottom topography, currents (such as the Gulf Stream), and local winds mold these deep-water waves into forms that are poorly predictable in many important circumstances, such an during storms. The constant change in waves as they move into shallow water and interact with each other and the sea bottom or seabed combines with the time variation ~ wave conditions to make description and prediction elusive. Winds drive and modify surface currents. Waves, as they bread and run up on beaches, drive currents that parallel the shore. Tides also contribute to the complexity of the nearshore envi- ronment. Near the many coastal inlets characteristic of the Atlantic and Gulf coasts of the United States, tides alter wave height and direction and coastal currents in an intricate fashion. Varying tidal elevations (m some areas exceeding 10 meters) cause the waves to act on different parts of a beach during low tide and high tide; sometimes the high-tide position can reach inland several kilometers. Topography Coastal engineering measurement systems are used to monitor the shape of the shoreline and submarine topography. A central diffi- culty in predictions based on these measurements is the interrelation of physical forces such as wind, waves, currents, and tides and the resulting responses. A wave may alter the bottom topography in an area, and that change in bottom topography can In turn change the characteristics of the wave. A common example is the nearshore sandbar. Under certain wave conditions, a nearshore bar is formed by moving sed~rnents from the beach out to deeper water, forming a local shoal. The presence of this shoal in turn changes the breaking characteristics of the incoming waves, causing them to break over the bar first instead of on the beach. This interaction or feedback is a limiting factor in our understanding of coastal processes. One cannot study waves by themselves, or bed forms by themselves, neglecting the other processes. Instead, this feedback requires the engineer to model or measure both the bed and the driving forces, a difficult theoretical and observational problem. Summary of Measurement Complexities The diversity of scales and the interactive nature of the water and shoreline complicate the design of coastal engineering measurement

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16 systems. Although measurement systems can be designed for specific conditions with some considerable success, it ~ doubtful whether a small number of instruments or techniques ever will be sufficient to make all the measurements coastal engineers require to perform their design tasks. The nature of the inner shelf-nearshore zone will require a diversity of techniques and approaches. Although some universal and versatile tools may be available for many coastal engineering applications, specialized tools always will be required to perform specific measurements or to provide predictions under certain conditions. ANALYTICAL METHODS IN THIS STUDY The purpose of this study was to identify the development needs for instrumentation and measurement systems ~ coastal eng~neer- ing. The committee gathered the available pertinent literature and analyzed and synthesized the results. A large volume of Formation had to be organized into meaningful and defendable conclusions and recommendations. Since an understanding of coastal engineering ret quirements involves such a diversity of measurements and modeling applied to a wide variety of coastal engineering projects, a scheme or structure was needed to organize and focus the results of this review. Determining that the most unportant measurements are those that are most needed to solve coastal engineering problems, the comurut- tee agreed on a structural approach that proceeded along the path shown ~ Figure Id. The committee saw this as a hierarchical analysm that is, each engineering problem has a variety of processes that must be under- stood, generally requiring a variety of measurements which in turn are used in engineering design or modeling to produce an engineering solution. The following example illustrates the approach used. ENGINEERING ISSUE: Design of a dredged harbor entrance channel. IMPORTANT PROCESSES AND MEASUREMENTS: PROCESS Sea Surface Molion and Level Wave Darameters MEASUREMENTS . . Direction or Height Period Directional Wave Energy Spectrum

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17 Tidal parameters. . Currents.. Storm Parameters . Storm conditions . . Elevation Magnitude Direction . Duration Strength Origin Runoff Volume I.ocation Type of sediment Volume Transport rate in suspension Transport rate by bed-Ioad From the literature and the individual experience of its members, the committee determined measurement and modeling capabilities in meeting the design requirements and, if necessary, identified the needs for further refinement or development. Some measurements are, of course, more critical than others; some can be measured with confidence (tides) and others not well at all (bed-Ioad sediment transport). Using this structured approach it was possible to see how each measurement requirement affected the solution to the engineering problem. Another consideration of importance to the measurement evalu- ation process is the difference in need that may arise from assessment of an applied engineering versus a basic research requirement. For example, the resolution of velocity and direction required for measur- ing longshore current ~ much less than that required for determining similar phenomena on a small scale (e.g., shear or drag forces). Of- ten the differences are not conflicting but simply represent immediate applied engineering needs versus the more subtle basic research re- quirements. In reviewing physical processes in the high-energy shore area such as wave breaking and its relation to wave-force effects, for example the committee noted where our theoretical understanding is weak. A comprehensive identification and assessment of all areas where theory is in doubt would be a large undertaking. In its as- sessment the committee chose to highlight those areas that have the greatest impact on the data required for coastal engineering. The remainder of this report applies the committee's analyti- cal approach (shown in Figure t-1) over the full range of coastal Sediment Movement

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18 Identify Engineering Issue 1. ~ 1 r - 1 Identify Important Processes r ~ Identify Measurement Requirements l ~ Assess Existing Capabilities 1 ' 1 Identity Development Needs FIGURE 1-1 Structural approach to collecting information on coastal engi- neering problems. processes that must be considered and understood by the engineer and those who are responsible for developing the technical basis for decision-making about the use and protection of our beach and coastal resources.