Engineered Streambeds for Induced Hyporheic Flow: Enhanced Removal of Nutrients, Pathogens, and Metals from Urban Streams

Abstract

The hyporheic zone (HZ) has the potential to mitigate nonpoint source pollution that threatens urban streams, but limited flows and inefficient interchange typically constrain its water quality improvements. This paper presents coordinated streambed hydraulic conductivity (K) modifications, termed Biohydrochemical Enhancement Structures for Streamwater Treatment (BEST), to efficiently drive interchange, attenuating nutrients, metals, and pathogens. Numerical models consisted of sandy HZ with high and low K streambed media components, and variable slope and in situ sediment K. BEST contaminant mitigation was estimated using hyporheic flow and residence time (RT) simulations and contaminant removal rate constants from literature for specific porous media. Hyporheic flows improved, whereas mean RT decreased approximately linearly with increasing slope and in situ K. Despite vast differences in flow and RT, contaminant removal potential was relatively consistent among BEST in which reaction time scales were similar to or shorter than RTs. However, BEST with excessive RTs were less efficient. Most contaminants could be attenuated within a series of BEST 50 m in length, suggesting that BEST could be an effective stormwater best management practice for small streams.