Quantifying evaporation in a permeable pavement system

Studies quantifying evaporation from permeable pavement systems are limited to a few laboratory studies and one field application. This research quantifies evaporation for a larger field application by measuring the water balance from lined permeable pavement sections. The U.S. Environmental Protection Agency constructed a 0.4ha parking lot in Edison, NJ, that incorporated three different permeable pavement types in the parking lanes - permeable interlocking concrete pavers (PICP), pervious concrete (PC) and porous asphalt (PA). An impermeable liner installed 0.4m below the surface in four 11.6m by 4.74m sections per each pavement type captures all infiltrating water and routes it to collection tanks that can contain events up to 38mm. Each section has a design impervious area to permeable pavement area ratio of 0.66:1. Pressure transducers installed in the underdrain collection tanks measured water level for 24months. Level was converted to volume using depth-to-volume ratios for individual collection tanks. Using a water balance approach, the measured infiltrate volume was compared to rainfall volume on an event basis to determine the rainfall retained in the pavement strata and underlying aggregate. Interevent evaporation created additional storage in the pavement and aggregate layers. Events were divided into three groups based on antecedent dry period (ADP) and three 4 month groups of potential evaporation based on historical monthly pan evaporation records. There was a significant difference in rainfall retained among the various combinations of ADP and potential evaporation groups. More rainfall was retained in the pavement and aggregate layers as time between events increased and during warmer months with larger potential evaporation. Average cumulative evaporation from the permeable pavement sections for 134 rainfall events in 24months was 5.2% of the cumulative rainfall volume, and the range was 2.4-7.6%. Each PC section had more annual evaporation than any individual PICP or PA section. While measureable, evaporation is a small contribution to the total water budget on an annual basis for these systems. Copyright (c) 2014 John Wiley & Sons, Ltd.