Abstract
Low Impact Development (LID) is an alternative to conventional urban stormwater management practices, which aims at mitigating the impacts of urbanization on water quantity and quality. Plot and local scale studies provide evidence of LID effectiveness; however, little is known about the overall watershed scale influence of LID practices. This is particularly true in watersheds with a land cover that is more diverse than that of urban or suburban classifications alone. We address this watershed-scale gap by assessing the effects of three common LID practices (rain gardens, permeable pavement, and riparian buffers) on the hydrology of a 0.94 km2 mixed land cover watershed. We used a spatially-explicit ecohydrological model, called Visualizing Ecosystems for Land Management Assessments (VELMA), to compare changes in watershed hydrologic responses before and after the implementation of LID practices. For the LID scenarios, we examined different spatial configurations, using 25%, 50%, 75% and 100% implementation extents, to convert sidewalks into rain gardens, and parking lots and driveways into permeable pavement. We further applied 20 m and 40 m riparian buffers along streams that were adjacent to agricultural land cover. The results showed overall increases in shallow subsurface runoff and infiltration, as well as evapotranspiration, and decreases in peak flows and surface runoff across all types and configurations of LID. Among individual LID practices, rain gardens had the greatest influence on each component of the overall watershed water balance. As anticipated, the combination of LID practices at the highest implementation level resulted in the most substantial changes to the overall watershed hydrology. It is notable that all hydrological changes from the LID implementation, ranging from 0.01 to 0.06 km2 across the study watershed, were modest, which suggests a potentially limited efficacy of LID practices in mixed land cover watersheds.
Highlights
Urbanization alters natural hydrological systems by altering stream channel networks, creating microclimates, and generating rapid runoff from precipitation and snowmelt events [1]
Model simulation results suggest reductions in peak flows and surface runoff, and increases in evapotranspiration and subsurface flow and infiltration, with all spatial configurations of Low Impact Development (LID) at the watershed scale. This is consistent with Gagrani et al [19], Fry and Maxwell [53], and Avellaneda et al [54], who reported similar effects on water balance components and peak flows after the placement of different LID practices in urban watersheds, with 42–55 percent impervious surfaces and drainage areas ranging from 0.2 km2 to 12 km2
The magnitudes of simulated water balance responses to LID placement in our watershed study were lower than other studies in strictly urban watersheds (e.g., Fry and Maxwell [53] and Avellaneda et al [54]) and more similar to a pilot study in a small suburban watershed (1.8 km2 ) of Cincinnati, Ohio, where retrofitted rain gardens and rain barrels did not result in substantial runoff reductions [55]
Summary
Urbanization alters natural hydrological systems by altering stream channel networks (e.g., channelization and burial), creating microclimates (e.g., urban heat islands), and generating rapid runoff from precipitation and snowmelt events [1]. These changes have direct impacts on surface and groundwater quantity and quality. Conventional urban stormwater management practices are often developed to control runoff and minimize flooding; these systems can be costly and may not directly address issues, such as reductions in infiltration and groundwater storage via impervious surfaces that may lead to urban flooding, erosion, and the degradation of water quality [2]. A goal of LID is to promote watershed resilience through “green” design [6]
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