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Advancing understanding and prediction of redevelopment impacts on stormwater runoff in semi-arid urban areas
Panos, Chelsea Lynne
Panos, Chelsea Lynne
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2020
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2021-06-04
Abstract
As the global urban population grows, cities are densifying by redeveloping previously developed spaces. “Smart growth” through redevelopment is increasing the impervious coverage of urban areas and impacting the hydrologic regime in uncertain ways. Cities are looking to update current stormwater management criteria, which often exempt redevelopments, based on data-driven decisions informed by watershed-scale hydrologic modeling. Future stormwater management strategies must also consider climate changes and flood mitigation via low impact development (LID). Using the Berkeley neighborhood of Denver, Colorado, we investigated the impacts of redevelopment land use change, along with climate change and LID implementation, on stormwater quantity using a high-resolution, calibrated Stormwater Management Model for PC (PCSWMM). The model includes 170 subcatchments and parcel-scale predictions of impervious cover change for three scenarios of future redevelopment.Simulations of design storms for multiple redevelopment scenarios predict that an increase of 1% in impervious area from redevelopment will increase surface runoff by 1.63% for the 2-yr, 24-hr design storm and by 0.91% for the 100-yr, 24-hr design storm resulting in greater relative flood risks for smaller storm events. When assessing the effectiveness of LID to mitigate increases in runoff from redevelopment, we found that model sensitivity to LID siting and routing parameters can impact the potential for meeting regulatory compliance. Relative sensitivity of runoff volume output to area treated and LID placement was found to be on average 3.0 and 11.2 times higher than the seven most sensitive physical LID and subcatchment parameters. Misunderstandings of model sensitivities can lead to costly decisions that are made based on modeling results. Finally, when assessing the combined impacts of redevelopment land use change and climate change on stormwater dual drainage system resilience, it was found that the system may be able to handle increases in runoff and flooding from redevelopment land use changes or climate changes alone, but likely not both. However, distributed LID implementation in conjunction with redevelopment provides a unique opportunity for increasing system resilience with a small LID footprint. All findings indicate a need to lower the current area threshold for requiring stormwater management with redevelopment within updated stormwater management criteria.
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