San Diego Bay TMDL Modeling

A Total Maximum Daily Load (TMDL) study is conducted for three estuary mouths in San Diego Bay that receive freshwater and particle-bound contaminant loads from the surrounding watersheds via three creeks: Chollas, Paleta and Switzer. These three estuary mouths are on the State of California’s 303(d) list of impaired waterbodies, which requires a TMDL study on total suspended solids (TSS), trace metals, polynuclear aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons (CHCs) in the estuary mouths.

For this study, joint efforts have been initiated by both Southern California Coastal Water Research Project (SCCWRP), Regional Water Quality Control Board (RWQCB)-San Diego, and Spawar Systems Center, San Diego (SSC Pacific). An integrated model is being developed that links the watershed model with a fate and transport model for the receiving Bay water. The land-based contaminant loads, along with the freshwater inflows, are simulated using LSPC, which is an EPA-approved watershed model. The model is set up at scales that can resolve both spatial and temporal variabilities, both dry and wet seasons will be simulated. The LSPC predicted freshwater inflows and contaminant loads at the mouths of the three creeks are linked to the CH3D model which simulates the hydrodynamics and fate and transport of these contaminants in San Diego Bay.

Capabilities (direct support):

• Fate/Transport
• TMDL Modeling

Applications:

• Model for TMDL study
• Simulation for designed load reduction scenarios
• Provide particulate loading source for long-term fate/transport in sediment

The integrated watershed (LSPC, left figure) and fate/transport (CH3D, right figure) model for TMDL at the mouths of three creeks, including Switzer, Chollas and Palate Creeks in San Diego Bay.