IMPACTS OF STORMWATER MANAGEMENT ON TEMPERATURE RESPONSE IN URBAN STREAMS

Temperature plays an important role in maintaining a healthy balance within stream ecosystems through influencing the lifespan of microorganisms, decomposition of plant matter, and reproduction habits of freshwater fish. During baseflow conditions, streams experience diurnal temperature fluctuations in response to radiative heating, but during storm events, urban runoff can produce a heat spike. Stormwater Control Measures (SCMs) discharge stored urban runoff during and after storm events at a controlled rate to reduce transport of contaminants such as oil, pesticides, nutrients and sediment. The primary focus of this study is to determine how SCMs affect the magnitude and duration of stream temperature response to precipitation. Stream temperature was recorded at five minute intervals at locations upstream and downstream of SCMs at three urban sites in Charlotte, NC. Magnitude was determined by analyzing change in temperature between pre-storm and peak storm conditions, while duration involved evaluating time taken to return to 5-day pre-event average temperature following a storm event. Multiple storms were recorded in summer 2012, and of these storm events that followed five clear weather days were further analyzed. Temperatures downstream of the SCMs were consistently higher than the upstream during baseflow and storm events. Temperature spikes marked the beginning of each storm event and were usually greater in magnitude upstream of the SCMs. Based on these storm events, it appears that SCMs can reduce temperature spikes experienced by urban streams in response to precipitation, conveying a potential ecological benefit.