| heal.abstract |
Estimation of runoff from windrow compost pads is a challenge due to the different hydrologic properties of the compost and pad, and moisture storage in the compost, both of which change with time. The surface of a compost pad is usually crushed rock on top of a compacted layer of clay. The curve number method is widely used for estimating runoff from rainfall, but because the porous layer of gravel promotes greater infiltration and subsurface drainage, this study investigated the effectiveness of this standard approach. Four curve number based methods are assessed for their utility in estimating drainage from a 7284-m2 windrow compost pad in Athens, Georgia, using 16 storm events. The methods estimate drainage using (1) a tabulated curve number, (2) a quasi-dynamic curve number based on the magnitude of the rainfall, antecedent rainfall, and areal coverage of the compost piles, (3) an asymptotic curve number, and (4) an average event-based curve number. Using the tabulated curve number, event runoff (r2 = 0.92) was consistently underestimated. A quasi-dynamic curve number improved the runoff estimation (r2 = 0.98). The asymptotic (r2 = 0.90) and event-based averaged (r 2 = 0.92) curve number methods performed comparable to the tabulated curve number method. Although curve numbers for maturing compost decreased from approximately 95 to 75 over time, this study recommends use of a conservative curve number = 95 for containment of design storms, while curve numbers of 70 to 75 may be appropriate for estimating average annual runoff from mature compost and the area necessary for land application of the pad runoff. © 2013 American Society of Agricultural and Biological Engineers ISSN 0883-8542. |
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