Propagation of inflowing urban stormwater pulses through reservoir embayments

Flashy hydrology and high solute loads in stormflow are well-studied effects of the built environment on urban streams. The physical and chemical interactions between inflowing stormwater of urban streams and their termination in large impoundments, however, is poorly understood. Determining the spatial distribution of urban stormwater in reservoirs is an important step in understanding the effects of the heat and contaminant loads in these systems, which provide multiple services for adjacent cities. Here, we show that signals of stormwater from a small urban stream can propagate more than 800 m from the stream mouth. Stormflow can also break down the thermal stratification that exists during non-storm periods. Because the relative volume of inflowing water relative to stored water in a reservoir embayment determines the distance stormwater propagates, management of both the urban landscape (which affects runoff volumes) and of reservoir water levels affects the spatial footprint of urban stormwater. The physical and chemical effects of stormwater may have significant implications for nutrient and pollutant transport through and biogeochemical reactions in reservoirs, as well as habitat for organisms and processing of organic matter and greenhouse gases in these dynamic ecosystems.