Urban Residential Surface and Subsurface Hydrology: Synergistic Effects of Low-Impact Features at the Parcel Scale

Accurately predicting the hydrologic effects of urbanization requires an understanding
of how hydrologic processes are affected by low‐impact development practices. In this study,
we explored how growing season surface runoff, deep drainage, and evapotranspiration on a
residential parcel are affected by several low‐impact interventions, including three
"impervious‐centric" interventions (disconnecting downspouts, disconnecting sidewalks, and
adding a transverse slope to the driveway and front walk), two "pervious‐centric"
interventions (decompacting soil and adding microtopography), and all possible "holistic"
combinations. Results were compared to both a highly and moderately compacted baseline
parcel under an average and a dry weather scenario for a temperate climate. We find that
under reasonable assumptions for highly compacted soil, pervious areas are a major source of
runoff and disconnecting impervious surfaces may be relatively less effective without
improving soil conditions. Under both highly and moderately compacted soil conditions,
combining efforts to decompact soil with impervious disconnection has a synergistic effect
on reducing surface runoff and increasing deep drainage and evapotranspiration. All
combinations of interventions enhance infiltration, but the partitioning of additional root
zone water between deep drainage and evapotranspiration depends on the weather scenario.
Importantly, when all low‐impact interventions are applied together, growing season deep
drainage is higher than that from a vacant lot with no impervious surfaces. We infer that
ecohydrologic interfaces between impervious and pervious areas are strong controls on urban
hydrologic fluxes and that high‐resolution, process‐based models can be used to account for
these interfaces and thereby improve predictions of the hydrologic effects of low‐impact
interventions.

准确预测城市化的水文效应，需明晰水文过程如何受低影响开发（low‐impact development）措施的影响。本研究以住宅地块为研究对象，探讨了生长季内该地块的地表径流（surface runoff）、深层渗漏（deep drainage）与蒸散发（evapotranspiration）如何受多种低影响开发干预手段的调控：包括3项“以不透水面为核心（impervious‐centric）”的措施——落水管断接、人行道断接，以及为车道与前步道增设横向坡度；2项“以透水面为核心（pervious‐centric）”的措施——土壤解压实与添加微地形；同时涵盖上述措施的所有可能“整体性”组合方案。
研究将上述干预结果，与温带气候下平均天气、干旱天气情景中的高压实度与中等压实度基准地块的基准结果进行对比。分析表明：在高压实度土壤的合理假设条件下，透水面是径流的主要来源；若未同步改善土壤条件，断接不透水面措施的效果相对有限。在高、中两种土壤压实度条件下，将土壤解压实与不透水面断接措施结合，可产生协同效应：既能减少地表径流，又能提升深层渗漏量与蒸散发量。
所有干预措施组合均可提升土壤入渗（infiltration）能力，但额外根区（root zone）水分在深层渗漏与蒸散发间的分配比例，取决于天气情景。值得关注的是，当所有低影响开发干预措施同时实施时，生长季的深层渗漏量高于无任何不透水面的空置地块。本研究推断，不透水面与透水面之间的生态水文界面（ecohydrologic interfaces），是调控城市水文通量（urban hydrologic fluxes）的关键因素；而高分辨率、基于过程的水文模型（process‐based models），可用于表征这类界面，进而提升低影响开发措施水文效应的预测精度。