SIMULATION OF DIKE REMOVAL/BREACHING TO RESTORE ESTUARINE WETLANDS HABITAT

摘要

Simulation of tidal hydrodynamics in marine wetlands or marshlands is complex because of wetting and drying of the habitat associated with movement of tide. During the flood tide, much of the habitat may be submerged. However, the water is drained through the inner wetland channels with the ebb tide exposing the tidal flats and marshlands. This causes failure of most commonly used coastal hydrodynamic models, which cannot handle intermittent wet and dry regions in the model domain. The U.S. Fish and Wildlife Service (USFWS) currently manages 1000-acres of the Nisqually National Wildlife Refuge (NWR) as freshwater wetlands, enclosed in a 20-foot-high, 7-mile-long dike. USFWS is evaluating the feasibility of converting the freshwater wetlands to estuarine habitat by a variety of alternatives including breaching and/or removing the surrounding dike. The hydrodynamic and transport model RMA-10 was used in this study with the "marsh-porosity" option to simulate flows and salinity transport at the Nisqually NWR wetlands. The marsh-porosity option in RMA-10 allowed continuous and stable operation of the model through neap and spring tides and helped evaluate a number of alternative dike configurations with varying degrees of wet and exposed dry surfaces. The model results showed that a fully functional tidal system with complete penetration of salinity was obtained when dikes were reduced down to grade.