A Model-Based Watershed Implementation Planning Tool for TMDL and Municipal Stormwater Permit Compliance in Orange County, California

Newport Bay, located in central Orange County, California, USA, is a precious natural resource for wildlife habitat, boat harbors, and recreation. However, it faces significant challenges to meet the numeric targets for many total maximum daily loads (TMDLs), including those for sediment, nutrient, bacteria, selenium, trace metals, legacy organochlorine pesticides, and others. The challenges are due to a heavily urbanized watershed, current and historical land uses, complex and numerous sources of pollutants, and unique climatological and hydrological nature of the region characterized by sparse but often intense storms and flashy stormwater runoff. With the wasteload allocations of these TMDLs specified in the municipal separate storm sewer system (MS4) discharge permits, the TMDL requirements will be key drivers of the MS4 permit compliance.