Water Resources Research Act Program

Details for Project ID 2020AL354B


Institute: Alabama
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $25,000 Total Non-Federal Funds: $52,877

Principal Investigators: Frances C. O'Donnell

Abstract: Stormwater management is integral to mitigating the impacts of urban development onwater resources. Proper design of stormwater drainage systems intends to quantify and addresshydrological changes created by increased imperviousness and changes in water quality. Thesponsors of any development or redevelopment project that exceeds 5,000 ft2 are required by lawto have a stormwater management plan to maintain or restore to the maximum extent technicallyfeasible (METF), the pre-development hydrology of the property (EPA 2009). This applies toboth water quality and water quantity and is achieved with stormwater best management practices(BMPs) which are structures and design characteristics that store and treat stormwater before it isreleased from the watershed. Porous pavements are a stormwater BMP that provide a stormwatersolution while serving as a functional component of a site (e.g. parking, roadway, etc.). Benefitsof porous pavement systems include reduction in the peak flow rate by flattening flow-durationcurves, decreasing pollution during hydrologic events, and lessening the temperature of localbodies of water due to runoff (Van Dam et al. 2015).Porous pavements have an open void structure allowing the infiltration of water throughthe medium. This is counter to a traditional pavement which is designed to be impermeable, thusleading to increased runoff. Porous pavements typically consist of three major types: porousasphalt, pervious concrete, or permeable pavers (Figure 1). Each of these surface types are placedover a drainage basin made up of stone or soil with a high porosity. Design considerations includethe size and depth of the pavement site required to meet hydrologic requirements, characteristicsof the soil medium (conductivity, porosity, etc.) beneath the pavement structure, external drainageif necessary, minimizing detained water effects on the surface materials (asphalt, concrete, pavers)or surrounding infrastructure, and traffic loading.A major challenge associated with porous pavements is the broad range of hydrologicbehavior observed in the literature which leads to uncertainty in the parameters used to calculatehydrologic function. This is shown in Figure 2 (Eger et al. 2017), which displays the partitioningof precipitation between runoff, infiltration, and evaporation for different porous pavementsystems and draws attention to the inherent variability between the systems. In most cases,hydrologic calculations for stormwater management use the Soil Conservation Service (SCS)Curve Number (CN) approach, which is a simple way to estimate the effect of changes in landcover on total runoff and flood peaks. CN values are specific to land cover types and soil groupsand range from 0 (all rainfall infiltrated under all conditions) to 100 (completely impervious). Forthese estimates to be reliable, an accurate CN value for each land cover type involved in theanalysis is needed (Leming et al. 2007). The limited studies that have measured CN empirically5 for porous pavements produced CN estimates ranging from 6 to 89 (Beisch and Foraste 2013, Beanet al. 2007).