| Abstrakt: |
As stormwater control measures (SCMs) capture surface runoff from impervious areas, a shift in the water balance and flow regime components may emerge in urban watersheds, but the amount of SCM treatment needed to detectably shift these components may vary. We used the Soil and Water Assessment Tool (SWAT) hydrologic model to assess the sensitivity of 16 hydrologic metrics as an increasingly dense rain garden SCM network was applied across the West Creek watershed, near Cleveland, Ohio (USA). As the area treated by SCMs increased, annual baseflow increases matched decreases in surface runoff, while water yield and evapotranspiration changes remained small. The stream's peak response to rainfall decreased with SCM implementation across storm sizes, ranging from the threshold rainfall depth (4.8 mm) to values higher than the design storm of a single rain garden (19 mm). SCM networks draining >20% of directly connected impervious area (DCIA) significantly decreased the magnitude of discharges with a return period of less than 1 year, the percentage of time above mean flow, and flashiness. Recession slopes and annual 1‐ and 7‐day low flows exhibited a slight response that fell within uncertainty limits of the model. Water balance and rainfall response metrics exhibited the greatest sensitivity to different intensities of stormwater management, while infrequent high and low flows were resistant to detectable change even at high levels of SCM treatment when model uncertainty was included. Plain Language Summary: When it rains on rooftops and pavements, stormwater runoff is generated because the rain cannot infiltrate or be used by plants in that location. This runoff changes the dynamics of urban streams, by increasing flooding and often decreasing streamflow between storms. Stormwater management techniques, like rain gardens, aim to restore the streamflow dynamics of urban streams to conditions similar to what existed prior to urbanization. We used a numerical model to find out how much of the urban landscape needed to have associated rain gardens to change the dynamics of different parts of the streamflow regime. For a watershed near Cleveland, Ohio, more than 20% of the rooftops and pavements must be connected to rain gardens before changes are detected in the stream. But even when most (71%) of the rooftops and pavements were connected to rain gardens, the lowest and highest flows of each year are not significantly changed. A combination of the way rain gardens were designed and uncertainty from the numerical model limits our ability to detect the effects of stormwater management on some streamflow dynamics. Key Points: Rain garden networks can alter water balances in an urban watershed, but many flow regime components may not change significantlyFlashiness, time above mean flow, and 1‐month peak flows can decrease significantly when 40% of directly connected impervious area is treatedCalibrating land surface slope in SWAT decreases prediction intervals but does not compensate for lack of explicit pipe model [ABSTRACT FROM AUTHOR] |
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