Predictability of Beach Nourishment Performance

by Robert G. Dean, Univ of Florida, Gainesville, United States,
Chulhee Yoo, Univ of Florida, Gainesville, United States,



Document Type: Proceeding Paper

Part of: Beach Nourishment Engineering and Management Considerations

Abstract:

Beach nourishment projects represent planform anomalies and are generally placed steeper than the natural profile. These disequilibrium conditions induce cross-shore and longshore sediment transport components that diminish both the dry beach width and the volume of sand remaining in the region placed. For projects of usual dimensions, the time scale associated with the cross-shore equilibration is much shorter than that for the planform. The equilibrium additional dry beach width is shown to depend primarily on quality and quantity of material added. The time required for a proportion of the material to be transported from the region placed by longshore transport is shown to proportional to the square of the project length and inversely proportional to the 2.5 power of the wave height. If sand is placed to depths greater than the waves can transport, so-called 'residual' bathymetry is left behind and, depending on its planform characteristics, can affect the quasi-equilibrium planform of the shoreline. This may explain, at least in part, erosional 'hot spots' that occur after beach nourishment and/or may offer an approach to controlling such phenomena. The use of retention structures to prolong the useful life of a beach nourishment project is reviewed. Projects placed on a seawalled beach exhibit significantly different behavior than those on a sandy beach. In particular, the planform anomaly migrates in the direction of net longshore sediment transport and the rate of spreading depends strongly on wave direction. Finally, estimates based on judgement and experience are presented for the predictability of two scenarios of beach nourishment projects.

Subject Headings: Littoral drift | Sediment transport | Beach protection and nourishment | Project management | Coastal management | Beaches | Water waves

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