H176-08
Wastewater discharges as a management tool to support beneficial uses of urban rivers

Tuesday, 15 December 2020: 07:28
Virtual
Jordyn Wolfand1, Daniel Philippus2, Reza Abdi2, Jennifer Taylor3, Katie Irving3, Kristine Taniguchi-Quan4, Eric D Stein3 and Terri S Hogue2, (1)University of Portland, Shiley School of Engineering, Portland, OR, United States, (2)Colorado School of Mines, Civil and Environmental Engineering, Golden, CO, United States, (3)Southern California Coastal Water Research Project, Costa Mesa, CA, United States, (4)Southern California Coastal Water Research Project, Costa Mesa, United States
Recorded Presentation
Abstract:
The Los Angeles River watershed, like many urban catchments, has been extensively modified for flood protection, water supply, stormwater management, and wastewater discharge. Because of its altered hydrology, the system supports beneficial uses that were not supported historically, and conversely, fails to support beneficial uses that were historically supported. As municipalities re-envision water reuse practices, we have an opportunity to consider how changes in wastewater discharge patterns could help support desired ecological or recreational uses.

A coupled hydrologic-hydraulic model was developed to investigate how reductions in wastewater discharge may impact environmental flow metrics associated with occurrence of native species and habitats. A daily, spatially distributed hydrologic model was created, calibrated, and validated in PCSWMM for water years 2011 to 2018. Hydrologic outputs were used as inputs to a steady-state hydraulic model, created in HEC-RAS, for the main stem of the Los Angeles River and two major tributaries (Compton Creek and Rio Hondo). Cross-sectional water profile data including discharge, velocity, depth, and shear stress were simulated at key locations under baseline and water reuse scenarios, which were defined for three wastewater treatment plants within the watershed. These hydraulic and hydrologic metrics were compared to those associated with occurrence of sensitive aquatic species, as well as those required to sustain recreational uses of the river.

Based on our analysis, urban baseflow, spring recession rate of change, average flow, and dry season duration are the most sensitive flow metrics to changes in wastewater reuse; least sensitive metrics include peak flow durations and frequencies. The approach successfully provided ranges of hydrologic and hydraulic variables that relate to suitable habitat for key species. Results allow us to maximize wastewater reuse while still supporting native species and recreation and show in some cases, management scenarios can both support reuse goals and ecology.

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