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The effects of water table, hydraulic loading ratio, and climate change on constructed wetland stormwater capture performance
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The effects of water table, hydraulic loading ratio, and climate change on constructed wetland stormwater capture performance

Lindsay Elizabeth Frazier
Master of Science (M.S.), Drexel University
May 2016
DOI:
https://doi.org/10.17918/etd-6906
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Abstract

Constructed wetlands--Runoff--Environmental aspects Constructed wetlands--Climatic changes--Environmental aspects Environmental Engineering
This paper investigates the effect of a high water table, hydraulic loading ratio (HLR), and climate change on a constructed wetland's (CW) water budget and stormwater capture performance. The 940 m2 CW receives runoff from a 6,880 m2 parking lot, with excess flows discharged to Meadow Lake, (Flushing, NY USA). Inflows to the CW include precipitation and parking lot runoff; outflows include evapotranspiration, infiltration, discharge through the low flow underdrain, and flow to the lake over the thelmar weir. Performance was investigated over a total of 14 pairs of wet and dry spells occurring between September 29th, 2015 and November 24th, 2015. Actual evapotranspiration rates were calculated using the Penman Monteith Equation, infiltration rates derived from observed wetland drawdown, and outflow based on classical hydraulic relationships associated with the various weirs and conduits installed. The water budget was computed daily. An EPA SMM model validated to the observations was used to simulate the performance of the facility over a typical rainfall year, and to model changes in CW performance due to increased HLR and climate change. Stormwater capture per event varies from 1.4% to 100% of inflows, respectively, with a mean of 76%. The model suggest a nearly linear, 0.7% reduction in the mean percent of event inflow retained for every one unit increase in HLR (r2=0.9). The modeling also suggests that the reduced performance of the site due to climate change is approximately equivalent to an increase in HLR of 58.9% (HLR=11.6). Hydraulic features such as low flow discharge pipes, and siting decisions such as associated with the designed tributary drainage area, can thus potentially be used to compensate for physical conditions such as the presence of a high water table and climate change that would otherwise reduce facility performance.

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