Global Climate Change Impacts in the United States 2009 Report Legacy site

It has been estimated that over 90% of the tidal freshwater wetlands of the Sacramento-San Joaquin Delta region in California, USA, have been leveed, removing them from tidal and floodwater inundation. One alternative for restoration of tidal freshwater marsh ecosystems is to reconnect regions currently managed for agricultural purposes to the adjacent rivers and sloughs. Two elements of such restoration efforts that have not been adequately addressed are the impact that restoration efforts are likely to impose on flood stages, and the extent of various habitat types that may develop. This study tests the hypothesis that habitat restoration and flood mitigation can be compatible. MIKE 11, a one-dimensional, unsteady hydraulic model is used to evaluate the flood stage impacts of five restoration scenarios for the McCormack-Williamson Tract, located in the northern Sacramento-San Joaquin Delta of California, USA. In addition to quantifying flood impacts, model results are used to quantify the volume of tidal exchange, and integrated with GIS to quantify the potential areal extent of subtidal, intertidal, and supratidal habitat zones within the project. The results indicate that the restoration would provide a mosaic of habitat types, and have a minimal adverse impact upon flood stages during a range of flooding conditions.