Engineered Hyporheic Zones as Novel Water Quality Best Management Practice: Flow and Contaminant Attenuation in Constructed Stream Experiments

Abstract:

The hyporheic zone is a hotspot for biogeochemical processing that can attenuate a variety of nonpoint source contaminants in streamwater. However, hyporheic zones in urban and agricultural streams are often degraded and poorly connected with surface water. In order to increase hyporheic exchange and improve water quality, we introduced engineered streambeds as a stormwater and restoration best management practice. Modifications to streambed hydraulic conductivity and reactivity are termed Biohydrochemical Enhancement structures for Streamwater Treatment (BEST). BEST are subsurface modules that utilize low- and high-permeability sediments to drive efficient hyporheic exchange, and reactive geomedia to increase reaction rates within the hyporheic zone. This work presents the first physical performance data of BEST modules at the pilot scale. BEST modules were installed in a constructed stream facility at the Colorado School of Mines in Golden, CO. This facility features two 15m artificial streams, which included an all sand control condition alongside the BEST test condition. Streams were continuously operated at a discharge of 1 L/s using recycled water. Time-lapse electrical resistivity surveys demonstrated that BEST modules provided substantially greater hyporheic exchange than the control condition. Water quality samples at the hyporheic and reach scales also revealed greater attenuation of nitrogen, coliforms, and select metals and trace organics by BEST modules relative to the control condition. These experimental results were also compared to previous numerical model simulations to evaluate model accuracy. Together, these results show that BEST may be an effective best management practice for improving streamwater quality in urban and agricultural settings.