Abstract
This research developed a new approach for calculating the area over which water spreads after being released from a confined conduit onto a sloped planar surface with defined roughness. In particular, the goal was to predict how stormwater would spread onto a sloped grass lawn after being discharged from a disconnected gutter downspout or through a parking lot curb cut. The need for this stems primarily from regulators increasingly requiring developers to infiltrate more of the runoff created by site development, but designers not having good tools for estimating the infiltration area associated with such “overflow” practices. The model is largely based on Manning’s equation applied at multiple cross-sectional areas of flow downslope, with additional modifications allowing the water to spread laterally. The model results were compared to laboratory experiments of water spreading across a roughened painted surface and two different artificial turfs. The new model predicted the wetting area with average absolute errors of 6.0% and 5.9% for a fine-bladed artificial turf and a coarse-bladed artificial turf, respectively. In addition, while validating the modeled flow spreading across a range of roughnesses, the model had an absolute error of 5.2% for a rough painted surface meant to represent unfinished concrete.
Highlights
Jurisdictions specified as Municipal Separate Stormwater Sewer Systems (MS4s) are increasingly promulgating stormwater regulations requiring that certain depths of rainfall be infiltrated on development sites (United State Environmental Protection Agency [1])
This base n value is typical for concrete (Chow, 1959), which was our target
10.2 cm, on the painted surface, the system was modeled per the description within the
Summary
Jurisdictions specified as Municipal Separate Stormwater Sewer Systems (MS4s) are increasingly promulgating stormwater regulations requiring that certain depths of rainfall be infiltrated on development sites (United State Environmental Protection Agency [1]). These stormwater control measures (SCMs) include rain gardens, green roofs, bioretention cells, subsurface infiltration galleries, and the like. For many types of new construction— suburban domestic housing—an appealing option is to disconnect gutter downspouts such that the roof runoff is directed across a grass lawn for additional infiltration. Most of the stormwater manual SCM descriptions (e.g., Tennessee Stormwater Manual [3])
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