California Zero Trash Policy and Its Impacts on Urban Drainage

The California Statewide Trash Amendments require that Phase I MS4 Permittees initiate retrofit programs to eliminate Trash in discharges from MS4s through the implementation of Trash Control BMPs. In addition, development projects are also required to incorporate LID BMPs that provide the full retention of the 85th-percentile storm runoff. This paper assesses how green infrastructure impacts compliance with the 100-year level of flood protection. Based on the findings of a literature review, two separate case studies were developed to assess the hydraulic impacts of green infrastructure. The implementation of infiltration chambers in an interior drainage pond located in the City of Oxnard resulted in a slight increase of the pond volume (1.3%) due to the loss in hydrostatic pressures on the outlet flap gate. Typical MS4 maintenance of catch basins are performed once to twice every year, when catch basins are 25% to 50% full. A 2D hydraulic model for the western part of the City of Simi Valley showed that a blockage factor of 25% would result in an additional 33 parcels in a designated flood zone. Maintenance and design recommendations are proposed to address these findings.