Beach Nourishment and Protection (1995) / Chapter Skim
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G Physical Processes Monitoring
G Physical Processes Monitoring
Pages 294-310
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From page 294... ...
Measurements may include both the forces that move sand and the response of the beach to these forces. However, many physical processes monitoring programs address only the response of a beach to these forces for example, beach profile changes and shoreline recession.
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From page 295... ...
One purpose of performance monitoring is to understand fundamental coastal processes and how they influence beach nourishment project performance for example, to understand how a project impacts adjacent areas as sand is moved along and across the shore.
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From page 296... ...
The physical data needed include measurement of waves, currents, water levels, beach profiles, and meteorological conditions. Construction monitoring might be undertaken to verify payment to a contractor, to ensure quality control, to obtain as-built information or to document construction practices and how they affect project performance.
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From page 297... ...
Long-term monitoring consists of systematic collection of physical data needed to support assessment of project performance and to guide the renourishment program. PHYSICAL PROCESSES MONITORING Monitoring the physical processes and their effects relevant to a beach nourishment project needs to be done within the framework of a sediment budget for
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From page 298... ...
~ ~ 'g"'0"'-' i" the project area and adjacent areas. A sediment budget expresses the principle of conservation of sand: sand is neither created nor destroyed.
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From page 299... ...
Numerical models of coastal processes are, in fact, the limiting case of sediment budget equations constructed for an infinitesimally small time interval and subsequently integrated over time. Numerical models apply knowledge of coastal processes to predicting sand movement within and out of a beach nourishment project.
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From page 300... ...
Profiles also need to be spaced closer to each other near the ends of nourishment projects to monitor end losses. Profiles outside of the project area need to be located in a manner so as to permit determination of how much sand is gained by adjacent beaches at the expense of the project.
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From page 301... ...
Profile surveys must be spaced close enough in time to define seasonal profile changes, beach response to storms, and long-term profile evolution. Survey frequency might also change during a monitoring program with more frequent surveys taken shortly after construction when changes are rapid and less frequent surveys taken later when changes are slower.
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From page 302... ...
................ FIGURE G- 1 Sea sled far measuring beach prohlos Tom the dry beach through [he surf zone to depth of closure.
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From page 303... ...
Beach profile errors are not cumulative, and an error made during one survey affects only that survey and possibly only a portion of the profile. Volume calculations made using erroneous profile data lead to errors in estimating volume changes, but those errors can be corrected by subsequent surveys.
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From page 304... ...
Wave data can be obtained by direct measurement or by using mathematical relationships that transform meteorological data such as atmospheric pressure fields or wind data into wave heights, periods, and directions.
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From page 305... ...
Tidal currents might be important in causing end losses from a nourishment project. Beach nourishment projects located near tidal inlets can be affected by flood and ebb currents; however, tidal currents at inlets are rarely measured during typical beach nourishment monitoring programs.
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From page 306... ...
Water-level data are available from NOAA for sites near most beach nourishment projects in the United States. For stations with long records, data on relative sea-level changes can also be obtained (Hicks, 1983~.
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From page 307... ...
In order to acquire sufficient data for analysis, monitoring programs must identify the types of structures present; · how they are constructed; · their planform, orientation, spacing, and height; · their effect on waves and currents; · their permeability to waves and sand; and · their effect on the stability of the beach nourishment project. The effects of structures on the stability of a beach nourishment project can vary over the project's lifetime.
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From page 308... ...
Real-time measurements are generally not needed for beach nourishment project monitoring, so GPS does not, at present, offer advantages over standard surveying techniques for measurements like profile surveys. In the future, however, as costs decline, accuracy improves, and DGPS is more widely adopted, it may prove to be an economical system for surveying nourishment projects.
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From page 309... ...
Periodic controlled vertical aerial photography can provide data on changes in the location of the shoreline and, using standard photogrammetric methods, can provide data on changes in the topography of the subaerial beach. Videotape can supplement regular photography and can also be used to document project conditions and performance before, during, and after storms.
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From page 310... ...
1994. Guidelines for surveying beach nourishment projects.
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