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6 Conclusions and Recommendations The Committee on Coastal Engineering Measurement Systems conducted this study with three objectives in mind: (1) to assess the needs for coastal data, (2) to determine the availability and suit- ability of instrumentation to meet these needs, and (3) to provide recornrnendations regarding specific development of coastal instru- ments and measurement systems. Because the modeling function has a fundamental role in analyzing and forecasting coastal changes, the committee was requested also to assess how the capability and practice of modeling of processes in the high-energy coastal waters influence the development of measurement systems. The committee was also responsible for providing guidance on measurement devel- opment priorities. The committee agreed that there is a pressing need for develop ment of instruments and measurement systems. There ~ a need for a commitment at the national level to stimulate and coordinate de- velopment of measurement systems and techniques. Presently, those who use instrumentation and measurement systems both scientists and engineers are few in number and operate at such limited fund- ing that industry interest in developmental technology is also slight. Yet the benefits that might accrue from more timely and accurate data can be of major value to national, state, and local coastal management interests. These interests are just beginning to be influ- enced by recent changes in public law that place major responsibility 95

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96 on local government to finance coastal works, which put increas- ing emphasis on the validity of the environmental impact estimates for coastal development and have extended the federal government's economic imvolvement in coastal erosion. A federal laboratory with extramural funding capability could serve the purpose of coordination and support for a national prm gram. The committee recognized that, at present, development of instruments and measurement systems is carried out on a small scale and is usually driven by individual research needs. Therefore, avail- ability and suitability of existing systems is often unknown to much of the potential user community. Thus, a need exists for a forum to provide information, collaboration, interaction, and coordination on measurement systems development. The committee agreed to 19 recommendations regarding specific development of coastal instruments and measurement systems. The committee used the procedure schematically represented in Figure 6-1, and recommendations were derived from a conclusion reached by a consensus of its members. Each committee member ranked these recommendations and prioritized them as high, medium, and low, based upon their perception of the need and expected benefits to be gained in solving coastal engineering challenges from a national perspective. These individual priorities were integrated to arrive at a consensus prioritization, accepted by the entire committee. Of the 19 committee recommendations,`4 were ranked as having high priority. Of the remaining 15 recommendations, 5 were ranked high-t~medium, 9 were ranked medium, and 1 was ranked medium- to-Iow priority. It is the committee's feeling that the 4 high-priority recommendations need to be supported at the national level in the immediate future. The 5 recommendations ranked high-to-medium are also regarded as essential to coastal engineering advancement for the rest of this century. The remaining recommendation, categorized as being medium-to-Iow priority, is important but applies to more limited areas of the coast. The four sections that follow present the prioritized recornmen- dations of the committee. Each recommendation is preceded by the specific related conclusion reached by the committee. HIGH-PRIORITY RECOMMENDATIONS CONCLUSION: Wave direction measurement techniques, either for

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97 r Identify | Engineering Issues I 1 I Identify l . Important Processes | I Identify Measurement Reouirements Assess Present Measurement Capabilities 1. art Identify Development Needs 1 ~ -'-''-a ~ I ~ Develop Conclusions Establish Recommendations, Ranking and Priorities Reach Consensus Integrate Conclusions and Recommendations Establish Final Recommendations FIGURE 6-1 Analytical process for development of conclusions and recom- mendations.

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98 deep or shallow water, do not provide the necessary resolution for accurate prediction of littoral processes. RECOMMENDATION: It is recommended that both in situ and remote-sensing systems, including radar and acoustic techniques, be explored and developed. CONCLUSION: There ~ a need for a U.S. coastal observation data base on height, period, and direction of ocean waves. RECOMMENDATION: It is recommended that a perma- nent national system be established for the measurement and timely dissemination of nearshore wave data to include height, period, and direction. CONCLUSION: Sediment-transport modeling (conceptual and math- ematical) in the nearshore zone is largely empirical and poorly veri- fied. RECOMMENDA TION: It is recommended that program- matic emphasis be placed; on theoretical improvement and rigorous fiield testing fin an interactive fashion} of existing sediment-transport models, while more physically based mod- els are derived and field-tested. CONCLUSION: There is no existing capability to reliably measure high-concentration sediment motions, especially within the region immediately above the mobile bed. RECOMMENDA TION: It is recommended that high-resolu- lion sediment transport measurement systems be developed for use in high-energy wave environments such as the surf zone and tidal inlets. HIGH-TO-MEDIUM-PRIORITY Rl:COMMl:NDATIONS CONCLUSION: There is a need for the development of both mea- surement and modeling capability for understanding the internal dynamics of rubble-mound structures. RECOMMENDATION: It is recommended that mathemati- cal modeling efforts be undertaken in combination with in situ measurements on the dynamics of rub6te-mound structures.

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99 CONCLUSION: Mechanics of breakwater failures are poorly un- derstood because of the unknown nature of the deformations and displacements of pieces of material in rubble-mound structures. RECOMMENDA TION: It is recommended that simultaneous measurements of pore pressures in breakwater cross-sections be recorded during storms. Pressure-measuring devices of adequate sensitivity are available, but means of deployment, protection, and transportation of data to safe off-site o~oser- vation stations need development. CONCLUSION: More and better data are needed on wave setup during storm events. RECOMMENDATION: It is recommended that measure- ments of wave forcing and sea-level response be made during storm events to quantify wave setup. CONCLUSION: Improved understanding and prediction of fluid tur- bulence ~ essential to improve prediction of coastal flows and sedi- ment transport. RECOMMENDATION: It is recommended that significant effort be directed toward developing instrumentation for mea- suring turbulence in the demanding nearshore environment. Concurrently, turbulence modeling must be extended to en- hance prediction of turbulence under conditions of waves, currents, and a movable bed. CONCLUSION: Adequate current data are needed for verification and further development of two-dimensional and three-dimensional limited-area circulation models. RECOMMENDATION: ~ is recommended that development of low-cost current meters and associated telemetry or record- ing systems be undertaken to provide a feasible means of ob- taining data vital to the verification and further development of two- and three-dimensional hydrodynamic models in the coastal region. MEDIUM-PRIORITY RECOMMENDATIONS CONCLUSION: There is a need for improved three-dimensional models of nearshore currents.

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100 RECOMMENDATION: It is recommended that an improved three-dimensional nearshore current model, including im- proved description of breaking waves and awash, foe devel- oped for complex Eathymetry, and that the necessary three- dimensional field data be acquired to verify the model. CONCLUSION: Quantification of tide and storm-surge phenomena requires measurement of currents in tidal inlets to supplement infor- mation on water levels. RECOMMENDAT ON: It is recommended that efforts be made to develop reliable current meters, which can be de- ployedF during either normal or storm events, for measuring low-frequency currents in tidal inlets. The use of acoustic- Doppler profilers, tomography, OF electromagnetic methods for monitoring volume transport in channels and inlets needs to toe explored. CONCLUSION: Existing storm-surge models that allow for overland flooding of tidal flats and upland vegetated areas are based on ad hoc methodology. Adequate field data do not exist to calibrate storm surge models. REGOMMENDATION: It is recommended that further de- velopment of storm-surge models be directed at improving the physical basis and numerical implementation for overland Doodling. A program of field; measurement should be con- ducted to provide data sets for calibration and verification. CONCLUSION: There is currently no welI-tested proven capability to measure, or to estimate accurately, boundary shear stress beneath combined waves and currents in shallow water. RECOMMENDATION: It is recommended that acoustic trav- e! time, acoustic-Doppler velocimeler, or laser-Doppler ve- locimeter techniques be improved so that adequate velocity profiles can be obtained in energetic rapidly varying Tow fields. Alternative technology (optical methods, hot-fiimJ, which may provide estimates of boundary shear stress under a broader spectrum of environmental conditions, should be pursued. CONCLUSION: Measurement of small-scale (centimeter to decime- ter) changes in bed topography are needed for understanding local scour around structures and bottom roughness.

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101 RECOMMENDATION: It is recommended that nonintru~vc (remoteJ techniques be developed to measure local scour and bed forms under a variety of wave conditions, including storm events. Higher resolution side-scan sonars, buried di~eren- tial pressure sensors, and other acoustic, optical, and laser techniques should be explored for this application. CONCLUSION: There is currently a capability to measure bathym~ try across the coast under low-to-moderate wave conditions. Present techniques for measuring bathymetry across the coast cannot be used under high storm-wave conditions. RECOMMENDATION: It is recommended that technologies for measuring nearshore loathymetry toe improved to aIlou' measurements under higher wave conditions. Development efforts should evaluate both remote-senstng methods and in situ optical and acoustic technologies for estimating beach profile changes over a full range of oceanic conditions. CONCLUSION: There is a need for development and field verification of an improved operational model for refraction/diffraction. RECOMMENDATION: It is recommended that an efficient, compulationally fast, operational numerical mode! for refrac- tion/diffraction be developed for the general case of complex bathymetry. CONCLUSION: Spacially dense measurement of wav~radiation stress (wave momentum) is needed in shallow coastal water to provide long-term, reliable, accurate data for predicting littoral processes. RECOMMENDATION: It is recommended that elope arrays toe improved to touter costs, by making them more compact or by utilizing self-recording or telemetry to eliminate shore cables. Other techniques should also foe pursue`' such as combined pressure sensor and velocity meters (PUV} and shorebased radars. CONCI,USION: Coupled short-wave/Iong-wave models are needed to increase predictability of complex nearshore flow fields, particu- larly around tidal inlets. Improvement must be made in the physical understanding of nonlinear wave/current interaction and wave inter- action with the bottom. Detailed velocity measurements in the field are required to provide data sets to validate these models.

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102 RECOMMENDA TION: It is recommended that existing short- wave/iong-wave coupled models incorporate more complete physics. Particular emphasis should be placed on modeling complex puid/bottom interactions near tidal inlets. Measure- ment programs should be initiated to provide wave height and measurements in sufficient detail to test these models. M~DIUM-TO-[OW-PRIORITYRECO~n~ENDATIONS CONCLUSION: Quantification of tsunami models, coastal tide mod- els, and shelf circulation models requires deep water pressure gauge measurements at Pacific locations, seaward of the continental slope. RECOMMENDATION: It is recommended that the benthic pressure measurement program be expanded to include a West Coast array. DEVELOPMENT NEEDS In the previous sections of this report we have identified several unsolved problems in coastal engineering. These problems exist due in part to our limited understanding of some of the processes impor- tant in coastal engineering. Our understanding is lirn~ted in some cases because of the measurement difficulties that are encountered in the coastal zone. This is indeed a difficult measurement environ- ment, with a wide range of space and time scales to be resolved. High data rates are needed to resolve the short-period processes, en c] long recording times are needec] to resolve the Tong-period processes. Since many of the processes of interest are two- or three-dimensional, the simultaneous operation of several sensors is also necessary. Often, measurements are needed in remote locations where in- strumentation systems must operate in an automatic mode. Until recently data had to be telemetered from a sensor to a recording site via cable through the surf zone. It was difficult to get long-term measurements because of cable failures, even though experience with West Coast wave measurements has shown that properly designed cables can survive many years. Recent advances in telemetry and data acquisition systems have overcome some of these problems. Measurements are most needed under high-energy conditions and close to the interfaces (sea surface, bottom, and structure). Remote-sensing techniques using radar and acoustic techniques may

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103 provide some means to improve such measurements. Many of the processes of interest are subject to numerical modeling, but in many cases the data needed to specify initial and forcing conditions have been lacking. Many of the processes of interest are nonlinear and in- teractive and require relatively complex physics in simulation models. Advances in computer technology and modeling make it feasible to mode} some of these processes if the data requirements for the models can be satisfied. In summary, recent developments ~ sensor technology, data telemetry, recording systems, and computers offer promise of signif- icant advances in the resolution of coastal engineering problems in the next decacle.

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