Downstream Dissipation of Storm Flow Heat Pulses: A Case Study and its Landscape-Level Implications
© 2016 American Water Resources Association. Storms in urban areas route heat and other pollutants from impervious surfaces, via drainage networks, into streams with well-described negative consequences on physical structure and biological integrity. We used heat pulses associated with urban storms as a tracer for pavement-derived stormwater inputs, providing a conservative estimate of the frequency with which these pollutants are transported into and through protected stream reaches. Our study was conducted within a 1.5-km reach in Durham, North Carolina, whose headwaters begin in suburban stormwater pipes before flowing through 1 km of protected, 100-year-old forest. We recorded heat-pulse magnitudes and distances travelled downstream, analyzing how they varied with storm and antecedent flow conditions. We found heat pulses >1°C traveled more than 1 km downstream of urban inputs in 11 storms over one year. This best-case management scenario of a reach within a protected forest shows that urban impacts can travel far downstream of inputs. Air temperature and flow intensity controlled heat-pulse magnitude, while heat-pulse size, mean flow, and total precipitation controlled dissipation distance. As temperatures and sudden storms intensify with climate change, heat-pulse magnitude and dissipation distance will likely increase. Streams in urbanized landscapes, such as Durham municipality, where 98.9% of streams are within 1 downstream km of stormwater outfalls, will be increasingly impacted by urban stormwaters.
Somers, KA; Bernhardt, ES; Mcglynn, BL; Urban, DL
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