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Use of Water Content Reflectometers in Bioinfiltration/Bioretention to Measure Water Movement and Estimate Evapotranspiration
Citation:
Brown, R. AND Mike Borst. Use of Water Content Reflectometers in Bioinfiltration/Bioretention to Measure Water Movement and Estimate Evapotranspiration. Presented at 2014 ASCE-EWRI World Environmental and Water Resources Congress, Portland, OR, June 01 - 05, 2014.
Impact/Purpose:
Most bioinfiltration/bioretention models assume runoff is evenly distributed across the surface area and after the engineered fill media is no longer saturated, the volumetric water content (VWC) is constant throughout the media profile and at field capacity. Four to nine water content reflectometers (WCRs) were spatially distributed across the surface and installed in profile in 15 systems located in Kentucky, New Hampshire, and New Jersey, to test these assumptions. The WCRs showed that the media VWC after drainage ended was not uniform with depth, and it was larger than the predicted field capacity based on soil texture. In addition, the spatially distributed WCRs documented that runoff from most storms infiltrated near the inlet. These observations and measurements which contradict the simplified modeling assumptions have important implications for bioretention design and plant selection and survival.
Description:
Most bioinfiltration/bioretention models assume runoff is evenly distributed across the surface area and after the engineered fill media is no longer saturated, the volumetric water content (VWC) is constant throughout the media profile and at field capacity. Four to nine water content reflectometers (WCRs) were spatially distributed across the surface and installed in profile in 15 systems located in Kentucky, New Hampshire, and New Jersey, to test the hydrologic model assumptions and monitor performance. These systems (two bioretention cells, six bioinfiltration areas, and seven tree boxes) have five different media blends with textures of sand, loamy sand, and sandy loam. The WCRs showed that the media VWC after drainage stopped was not uniform with depth. This was expected because field capacity is not a soil-water constant; VWC varies with depth based on suction from underlying groundwater. When the measured VWC was compared to field capacity predicted based on soil texture and organic matter content, the measured VWC was larger than the predicted field capacity, resulting in less available storage in the media than predicted. Finally, the spatially distributed WCRs documented that runoff from most storms infiltrated near the inlet. These observations and measurements which contradict the simplified modeling assumptions have important implications for bioretention design and plant selection and survival.
