Soil moisture dynamics and their effect on bioretention performance in Northeast Ohio

Most members of the Watershed Hydrology lab chose to go to GSA this year, and we had a blast sharing our science and enjoying Vancouver and surrounding areas. But now we are sadly missing out on the American Geophysical Union (AGU) meeting going on this week. Fortunately, a small piece of our work will be represented by outstanding summer REU student Sidney Bush. She’s giving a poster on Thursday afternoon in the Moscone West poster hall at H43F-1017. Here’s her abstract:

Soil moisture dynamics and their effect on bioretention performance in Northeast Ohio

Sidney A. Bush1, Anne Jefferson2, Kimberly Jarden2, Lauren E Kinsman-Costello2 and Jennifer Grieser3, (1)University of Virginia Main Campus, Charlottesville, VA, United States, (2)Kent State University Kent Campus, Kent, OH, United States, (3)Cleveland Metroparks, Parma, OH, United States

Urban impervious surfaces lead to increases in stormwater runoff. Green infrastructure, like bioretention cells, is being used to mitigate negative impacts of runoff by disconnecting impervious surfaces from storm water systems and redirecting flow to decentralized treatment areas. While bioretention soil characteristics are carefully designed, little research is available on soil moisture dynamics within the cells and how these might relate to inter-storm variability in performance. Bioretentions have been installed along a residential street in Parma, Ohio to determine the impact of green infrastructure on the West Creek watershed, a 36 km2 subwatershed of the Cuyahoga River. Bioretentions were installed in two phases (Phase I in 2013 and Phase II in 2014); design and vegetation density vary slightly between the two phases. Our research focuses on characterizing soil moisture dynamics of multiple bioretentions and assessing their impact on stormwater runoff at the street scale. Soil moisture measurements were collected in transects for eight bioretentions over the course of one summer. Vegetation indices of canopy height, percent vegetative cover, species richness and NDVI were also measured. A flow meter in the storm drain at the end of the street measured storm sewer discharge. Precipitation was recorded from a meteorological station 2 km from the research site. Soil moisture increased in response to precipitation and decreased to relatively stable conditions within 3 days following a rain event. Phase II bioretentions exhibited greater soil moisture and less vegetation than Phase I bioretentions, though the relationship between soil moisture and vegetative cover is inconclusive for bioretentions constructed in the same phase. Data from five storms suggest that pre-event soil moisture does not control the runoff-to-rainfall ratio, which we use as a measure of bioretention performance. However, discharge data indicate that hydrograph characteristics, such as lag time and peak flow, are altered relative to a control street. This analysis suggests that street-scale implementation of bioretention can reduce the impact of impervious surface on stormflows, but more information is needed to fully understand how soil moisture of the bioretentions affects inter-storm variability in performance.

Sidney’s poster is part of a session on “Water, Energy, and Society in Urban Systems” that Anne nominally helped convened. Check out all of the stimulating morning talks and awesome afternoon posters on Thursday. The rest of us are sorry to be missing it, but if *you* are in San Francisco at AGU this week, don’t miss out on all the great science in the session.

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