cbec was recently contracted by Moosa Creek, LLC, who proposes to develop the Moosa Creek Mitigation and Conservation Bank (mitigation bank) to rehabilitate, re-establish, establish, and enhance wetlands, riparian floodplain, and upland buffer along the San Luis Rey River and Moosa Creek.

In addition to wetland and stream resources, the mitigation bank is proposed to provide mitigation for federally and state listed species, including the coastal California gnatcatcher, least Bell’s vireo, southwestern willow flycatcher, and arroyo toad. The mitigation bank is located approximately 12 miles northeast of Oceanside, San Diego County, CA near the confluence of the San Luis Rey River and Moosa Creek, and will be developed in two phases.

Phase 1 will re-establish hydrologic connectivity and enhance ecologic habitats. Additional mitigation opportunities exist in adjacent parcel, between Moosa Creek and the San Luis Rey River that will be developed under Phase 2 of the project.

Construction activities will include grading and removal of topsoil associated with the San Luis Rey Downs Resort Golf Course to restore floodplain connectivity along the San Luis Rey River and Moosa Creek and restore riverine wetland, seasonal wetland, riparian wetland habitat, and non-wetland riparian habitat. Riparian and upland areas will be replanted with a combination of cuttings and nursery container plants and seeds to restore native vegetation.

cbec assisted in developing the proposed concept design for Phase 1 and Phase 2 by assessing the geomorphic and hydraulic feasibility of the proposed concept design for the mitigation bank. To inform the baseline, cbec conducted field studies to include establishing three stream gauging wells to coincide with the groundwater well transects, collecting bed sediment data, and surveying Moosa Creek, the San Luis Rey River, and adjoining floodplains with RTK GPS to replace and/or verify the photogrammetric data. cbec performed a rigorous hydrologic analysis to establish appropriate design flows for geomorphic / ecological conditions and flood conditions.

A detailed 2D hydrodynamic model of the study area was developed using MIKE21FM, which was used to inform the development of the restoration concept and evaluate the feasibility of specific features based on the 2-, 5-, and 1-year design hydrology. The 2D model was also used to evaluate the hydrodynamic effects of the proposed mitigation bank concept under the 100-year design flood within the project site as well as upstream and downstream of the project site to demonstrate that the project was not impeding flood conveyance.

As the proposed concept is refined, the model will be rerun to reflect proposed changes in topography and vegetation distribution and density.