Influence of Stormwater Control Measures on Hydrology and Water Quality in a Small Suburban Watershed

Rachel D Scarlett, Purdue University

Abstract

Healthy streams create vital habitat for aquatic communities and function as essential components of hydrologic and nutrient cycles. Urban streams are ecologically deteriorated due to increases in impervious area, discharge and pollutant loads from modified drainage networks, including piped water infrastructure, stream straightening, and stream burial. The resulting increases in discharge volume and intensity, and degraded water quality in urban areas have immense impacts on aquatic life and eutrophication downstream. These qualities allude to urban stream syndrome, a pertinent and consistent observation across cities. Although urban stream syndrome suggests that urbanized watersheds function as dominant transporters of material and energy to the watershed outlet, there is evidence that urban streams can also be assimilative ecosystems that process and cycle nutrients. In addition, water retention structures in the terrestrial landscape, specifically stormwater control measures (SCMs), facilitate evapotranspiration, delay runoff to the stream, and increase processing time for nutrients— like phosphorus and nitrogen. Natural analogs of SCMs— including riparian and upland wetlands with ephemeral or permanent hydrologic connectivity to streams, and hyporheic-zone processes— provide assimilative and storage functions in non-urban, less-impacted stream networks. Loss of these natural analogs with increasing urbanization contributes to the transition from assimilation to transporter functionalities in urbanized watersheds. While the effects of individual SCMs are well known, there is a knowledge gap on the cumulative influence of SCMs on hydrology and water quality. My hypothesis is that increases in volumetric SCM storage will drive urban watersheds from primarily water and nutrient transport systems towards assimilative systems, where N and P concentrations are reduced and flashy hydrology is dampened. To test this hypothesis, storm discharge and water chemistry were monitored at high temporal resolution along a gradient of SCM treatment in a small suburban watershed in Charlotte, NC. Results indicate that SCM mitigation was not a significant predictor of storm runoff volumes, nor was it a significant predictor of solute concentrations. However, indicators of water retention and nutrient assimilation were observed under dry antecedent conditions.

Degree

M.S.A.B.E.

Advisors

McMillan, Purdue University.

Subject Area

Environmental engineering

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