HYDROLOGIC AND HYDRAULIC FEASIBILITY ASSESSMENTS FOR ECOLOGICAL RESTORATION: THE GIACOMINI WETLAND RESTORATION PROJECT, POINT REYES NATIONAL SEASHORE, CA

Point Reyes National Seashore (Seashore) is planning a wetland/riparian corridor restoration project for the former 500-acre Giacomini Ranch at the south end of Tomales Bay, California. Logging and forest land conversion within the contributing Lagunitas-Olema Creek watersheds have significantly increased sediment production and deposition within portions of the Project Area, while channel realignment and levee creation in the Project Area has shifted the main delta depositional fan further into Tomales Bay. As a result, a large mosaic of former tidal salt-marsh habitats have been filled and converted to alternate habitat types, including uplands and freshwater marsh. The primary restoration goal identified by the Seashore is to restore natural tidal and freshwater hydrologic processes in a significant portion of the Project Area, thereby promoting restoration of natural ecological processes and functions. The Seashore is also committed to take a watershed-based approach to restoration such that it will emphasize opportunities to improve conditions with the entire Tomales Bay watershed.

A broad suite of field monitoring and investigation activities were conducted to characterize historic and existing geomorphic, hydrologic and water quality conditions in the Study Area and vicinity. Using this information along with results of baseline studies on existing wildlife, vegetation, wetland, and cultural resources, a range of restoration alternatives were developed that re-establish and optimize the hydrologic and ecologic function of a combination of tidal marsh, fluvial, freshwater wetland, riparian, and upland habitats in the Study Area. One significant challenge of the hydrologic design process was to balance sedimentation processes and flow dynamics to create a self-maintaining channel system that promotes restoration of natural ecological processes. A MIKE 11, one-dimensional hydrodynamic model was used as an integral tool to complete fluvial and tidal hydraulics, flood analyses, water quality, and sediment transport analyses. Other technical challenges faced included identifying restoration components that would promote desired channel and flood plain evolution along low-gradient reaches and, in turn, predicting trajectories for long-term geomorphic evolution.