Physical factors affecting the siting of dredged material islands

Dredge material islands are significant features formed very rapidly in comparison to normal geologic processes. Most geologic, engineering, and environmental studies of dredging and dredged material islands are short term analyses directed toward their environmental impacts. Since these islands are located in a dynamic environment, geologic processes actively erode, transport and redistribute the island material. In many cases, the siting of islands contributes to increased maintenance dredging due to the redistribution of sediment. It would be desirable to site the islands so that the sediment does not contributeto channel infilling. A study of the affect of geologic processes on the redistribution of island sediment has identified ten physical factors that should be considered in selecting disposal sites in bays and lagoons. These factors include: wind; waves; tidal fluctuations, both astronomic and wind; currents, both fluvial and tidal; the physical characteristics of the dredge material; climate of the area; physiography of the basin; islands design, shape and height; affects of man, such as ship wake and land subsidence; and the biology of the site, both flora and fauna. These ten factors were found to interact in a complex manner that cannot easily be quantitatively evaluated. As-a-result, the physical environmental data needed for the selection of disposal sites or sites for island construction will remain a geological art rather than mathematical calculation.