Simulation of Beach Hydraulics for Smith Island, Prince William Sound, Alaska

We investigated beach hydraulics in a gravel beach on Smith Island, Prince William Sound, Alaska that was previously polluted with the Exxon Valdez oil spill in 1989. The beach contains Heavy Oil Residue (HOR) in the lower intertidal zone. The slope of the beach decreases in the seaward direction. Measurements of water pressure and salinity were analyzed and simulated using the model SUTRA (Saturated-Unsaturated Groundwater Flow and Solute Transport Model). The results indicated that the beach consists of two layers with contrasting hydraulic properties: an upper layer with a high hydraulic conductivity, on the order of a few centimeter per second and a lower layer whose hydraulic conductivity is around three orders of magnitude lower. The lingering of oil in the lower intertidal zone is probably due to the decrease in slope in that region, which resulted in small flow in that region that brings nutrients and oxygen to the oil. Thus, it is likely that the oil has not degraded due to stochiometric limitation rather than kinetic limitation.