Abstract
Urbanization causes alteration of the thermal regime (surface, air, and water) of the environment. Heated stormwater runoff flows into lakes, streams, bays, and estuaries, which potentially increases the base temperature of the surface water. The amount of heat transferred, and the degree of thermal pollution is of great importance to the ecological integrity of receiving waters. This research reports on a controlled laboratory scale test to assess low impact development (LID) stormwater control measure impacts on the thermal characteristics of stormwater runoff. We hypothesize that LID stormwater control measures (SCMs) such as pervious surfaces and rain gardens/bioretention can be used to mitigate the ground level thermal loads from stormwater runoff. Laboratory methods in this study captured and infiltrated simulated stormwater runoff from four infrared heated substrate microcosms (pervious concrete, impervious concrete, permeable concrete pavers, and turf grass), and routed the stormwater through rain garden microcosms. A data logging system with thermistors located on, within, and at exits of the microcosms, recorded resulting stormwater temperature flux. Researchers compared steady state temperatures of the laboratory to previously collected field data and achieved between 30% to 60% higher steady state surface temperatures with indoor than outdoor test sites. This research helps establish baseline data to study heat removal effectiveness of pervious materials when used alone or in combination as a treatment train with other stormwater control measures such as rain gardens/bioretention.
Highlights
Urbanization is the conversion of rural land to a higher population and building density uses that typically have less vegetated and impervious surface than rural land
That appears to be a delay caused by a thermal gain that we have previously described as a “thermal flush”or “thermal spike,” which is similar to the contaminant or nutrient flush observed after the first moments of a typical stormwater runoff event [41]
The multi-disciplinary approach used for these studies has provided new information that may be used as baseline information to effectively mitigate stormwater thermal loads using low impact development (LID) stormwater control measures (SCMs)
Summary
Urbanization is the conversion of rural land to a higher population and building density uses that typically have less vegetated and impervious surface than rural land. Numerous early authors including Wheater et al, Laenen, Booth and Reinelt, Schueler and Arnold, and Gibbons [1,2,3,4,5] quantified the hydrologic effects of urbanization. Numerous other researchers including Omernik [7], Jordan et al [8], Haith and Shoemaker [9], Osborne and Wiley [10], Kronvang [11], and Correll et al [12] documented the impact of storm events and land use practices on stream contaminant loads such as sediments and nutrients. Hydrology 2019, 6, 16 and proposed impervious surface coverage as an indicator of urban stream health [13]. Despite expanding awareness of aquatic ecology and related biological and engineering disciplines throughout the 1990s, measurements of stream temperature and thermal loads were not studied in earnest in most urban stream studies until the 21st century
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