PREDICTIVE MODELING OF MIXED SEDIMENT CAP STABILITY DURING STORMS

摘要

The U.S. Army Corps of Engineers (USACE) assisted in design of a confined aquatic disposal (CAD) facility for storage of contaminated sediments in an existing borrow pit in Los Angeles/Long Beach (LA/LB) Harbor. A number of studies were conducted to define various design parameters and address regulatory agency concerns. One of these studies was performed to predict potential storm-induced erosion from capped sediments placed in one CAD cell. The proposed capping material is a nearby mixed sediment deposit of sand, silt, and clay. Field and laboratory experiments were performed to develop site-specific erosion rate algorithms for the proposed cap sediment as a function of shear stress and bulk density (depth below the sediment-water interface). Models were applied to simulate time histories of current and wave conditions inside the harbor for storms of record between 1970 and 1990. The erosion algorithms were incorporated into the USACE Long Term FATE of dredged material (LTFATE) model to predict cap erosion during each storm. Erosion tests indicated that the proposed cap material is more resistant to erosion than pure sand due to the approximately 10% clay-size content. Simulations indicated that the cap would partially erode but maintain coverage during energetic storms.