Evaluating the Effectiveness of Best Management Practices in the Los Angeles River Watershed

Best management practices (BMPs) are now an essential component of urban infrastructure as impermeable surfaces have disrupted the natural hydrology in developing watersheds. BMPs can be used to offset the extreme changes to surface flow due to urbanization. In this work, a series of infiltration basins were added to a hydrologic model to evaluate their effect on the urban hydrology of the Los Angeles River watershed. The watershed was represented using EPA’s BASINS model that extracted the river network and existing land cover patterns, geomorphology, and other physiological features using remotely sensed observations. Hydrologic simulations were conducted using the Environmental Protection Agency’s (EPA) hydrologic simulation program—Fortran (HSPF). Calibration results demonstrate reasonable representation of annual streamflows and storm peak flows when compared to historical observations. After calibration, percent land cover was allocated to the infiltration basins (increasing from 0 to 6) in an attempt to lower streamflows to pre-urbanization levels. Results of the model indicate that BMPs do reduce streamflows within the channel; however, there is an effective threshold—flows exceeding the threshold are not reduced (in some cases they increase), and flows below the threshold are reduced. As we increase the number of BMPs, there is not an increase in effectiveness as originally hypothesized. We found that infiltration basins will not sufficiently reduce streamflows within the Los Angeles River watershed. In future work, we will explore the inclusion of other BMP types and placement in an effort to reduce hazardous flows in the face of an uncertain climate.