Economic & Floodplain Assessment
  San Diego Creek | FEMA Support | 2D Flood Modeling | American River Watershed Floodplain Studies

On behalf of the Orange County Watershed and Coastal Resources Division, a study was performed to define the 100-year floodplain from I‑405 to Jamboree Road.  Existing hydrologic information was utilized and a HEC-RAS model was developed using new topographic information outside of the main channel banks and an assessment of the Manning’s n-value of the channel and floodplain.

Three scenarios were modeled as part of this study:

Scenario 1-With Levee and 40-foot Vegetation Buffer:  This scenario assumes the levees along both channel banks remain in place and do not fail during a 100-year storm event.  It also assumes that the existing vegetation along the toe of the east bank is maintained at 40 feet wide from Jamboree Road up to the I-405 Freeway.

Scenario 2-Failed Levee and 40-foot Vegetation Buffer:  This scenario assumes the levees along both channel banks are ineffective and fail during a 100-year storm event.  It also assumes that the existing vegetation along the toe of the east bank is maintained at 40 feet wide from Jamboree Road up to the I-405 Freeway.

Scenario 3-With Levee and Existing Vegetation Buffer:  The levees along both channel banks remain in place and do not fail during a 100-year storm event.  The width of the in-channel vegetation buffer is 40 feet wide upstream of Campus Drive.  Downstream of Campus Drive the width of the in-channel vegetation buffer was modeled to reflect existing conditions.  Calculations were made to determine the volume of flow that left the main channel and stage-storage curves were developed for the floodplain to determine the flooded area.

Mapping was produced for each scenario to show the floodplain area associated with the 100-year storm event under the scenario conditions.