Concrete Channel vs. Natural Arroyo—Stormwater Management Strategies and Potential Impacts on Water Resources

In their original state, watersheds in the Middle Rio Grande area drain stormwater runoff through a network of natural stream channels or arroyos. Historically, flood control strategies focused on the most efficient ways to convey stormwater runoff through populated areas, resulting in the conversion of many arroyos to hard-lined channels. Due to the increasing cost of traditional construction and concerns for the environment, local agencies started to consider stormwater management approaches that preserve arroyos in as natural a state as desirable, taking advantage of naturally high infiltration rates in arroyos and their potentially beneficial effect on water quality and groundwater recharge. The purpose of this study was to explore the potential impact of transmission losses, i.e., infiltration into the arroyo bed as a flood wave moves downstream, on flood hydrographs. A hydrologic model was prepared for a gauged watershed in Sandoval County, New Mexico, and model results were compared to measured flow data. The comparison shows that transmission losses can explain some of the discrepancies between simulated and measured runoff resulting from small storm events. Stormwater management strategies with focus on preservation of natural arroyo systems and potential implications on infiltration and runoff volumes are discussed in the context of increasing urbanization. The increase of impervious coverage in a watershed not only leads to higher runoff volumes for a given storm event, but also increases the frequency of runoff events and thereby the potential importance of transmission losses.