Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2007
Publication Date: 10/1/2007
Citation: Pappas, E.A., Smith, D.R., Huang, C., Shuster, W.D., Bonta, J.V. 2007. Impervious surface impacts to runoff and sediment discharge under laboratory rainfall simulation. Catena. 72:146-152.
Interpretive Summary: As land becomes developed for urban and suburban uses, rooftops and pavement replace natural or farmed landscapes. Precipitation that falls on rooftops and pavement quickly runs off, instead of infiltrating into the soil as it would generally do in a natural or farmed landscape. This often results in flooding and increased soil erosion. Rainfall simulations were performed on boxes of soil comprising 4 m slope lengths with impervious surfaces located either at the top or the bottom of the slope. Results indicated that paving the top of a slope would result in significantly more erosion than paving the same total area at the bottom of the slope. At lower rainfall intensities, paving the bottom of the slope generated more water runoff, since that water had no opportunity to infiltrate into soil, but at higher rainfall rates and when soil had been largely saturated, no hydrologic differences were detected. Results from this study will help guide the implementation of treatments and interpretation of results in related field research. The impact of this work will be improved land use management decision making ability, and these results will assist in USEPA’s regulatory decision making in storm water management and storm water prediction technologies.
Technical Abstract: Urbanization of watersheds previously managed for agricultural uses results in hydrologic changes associated with increased flooding and erosion. Few studies have been conducted to quantify these effects under controlled conditions and standard rainfall simulation methodologies have not been previously established. In this study, laboratory rainfall simulation methods on modular segmented soil boxes were developed and utilized to evaluate hydrologic and erosional responses to various impervious surface treatments. Results indicate that sloped plots having peripherally-located (upslope) impervious surfaces generated eroded sediment at approximately 2 times the rate of plots having channel-located (downslope) impervious surfaces at 25% imperviousness and at 5 times the rate at 50% imperviousness. Peripheral development resulted in initially lower water runoff rates than channel development, but this effect was dependent upon soil moisture and rainfall intensity, and did not account for large sustained differences. These results suggest that impervious surfaces should not be located at the periphery of watersheds receiving typically heavy rainfall rates, or having moderate to steep slopes and / or highly erodible soil.