We report an empirical analysis of the hydrologic response of three small, highly impervious urban watersheds to pulse rainfall events, to assess how traditional stormwater management (SWM) alters urban hydrographs. The watersheds vary in SWM coverage from 3% to 61% and in impervious cover from 45% to 67%. By selecting a set of storm events that involved a single rainfall pulse with >96% of total precipitation delivered in 60 min, we reduced the effect of differences between storms on hydrograph response to isolate characteristic responses attributable to watershed properties. Watershed-average radar rainfall data were used to generate local storm hyetographs for each event in each watershed, thus compensating for the extreme spatial and temporal heterogeneity of short-duration, intense rainfall events. By normalizing discharge values to the discharge peak and centring each hydrograph on the time of peak we were able to visualize the envelope of hydrographs for each group and to generate representative composite hydrographs for comparison across the three watersheds. Despite dramatic differences in the fraction of watershed area draining to SWM features across these three headwater tributaries, we did not find strong evidence that SWM causes significant attenuation of the hydrograph peak. Hydrograph response for the three watersheds is remarkably uniform despite contrasts in SWM, impervious cover and spatial patterns of land cover type. The primary difference in hydrograph response is observed on the recession limb of the hydrograph, and that change appears to be associated with higher storm-total runoff in the watersheds with more area draining to SWM. Our findings contribute more evidence to the work of previous authors suggesting that SWM is less effective at attenuating urban hydrographs than is commonly assumed. Our findings also are consistent with previous work concluding that percent impervious cover may have greater influence on runoff volume than percent SWM coverage.

中文翻译：

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评估城市降雨径流对雨水管理范围的响应

我们报告了三个小型、高度不透水的城市流域对脉冲降雨事件的水文响应的实证分析，以评估传统的雨水管理 (SWM) 如何改变城市水文过程线。流域的 SWM 覆盖率从 3% 到 61% 不等，不透水覆盖率从 45% 到 67% 不等。通过选择一组涉及单个降雨脉冲的风暴事件，在 60 分钟内交付的总降水量超过 96%，我们减少了风暴之间的差异对水文过程响应的影响，以隔离可归因于流域特性的特征响应。流域平均雷达降雨数据用于为每个流域中的每个事件生成局部风暴气象图，从而补偿短时强降雨事件的极端时空异质性。通过将流量值归一化为流量峰值并将每个流量过程线以峰值时间为中心，我们能够可视化每个组的流量过程线的包络线，并生成具有代表性的复合流量过程线，以便在三个流域之间进行比较。尽管流域面积在这三个源头支流中排放到 SWM 特征的比例存在巨大差异，但我们没有找到强有力的证据表明 SWM 导致水文过程线峰值的显着衰减。尽管 SWM、不透水覆盖和土地覆盖类型的空间模式存在差异，但三个流域的水文图响应非常一致。水文过程线响应的主要差异是在水文过程线的后退边上观察到的，并且这种变化似乎与流域中更高的风暴总径流有关，更多的区域排放到 SWM。我们的发现为之前作者的工作提供了更多证据，表明 SWM 在衰减城市水道过程线方面的效果不如通常假设的那么有效。我们的发现也与之前的工作一致，即不透水覆盖百分比可能比 SWM 覆盖百分比对径流量的影响更大。