An instantaneous unit hydrograph for estimating runoff from windrow composting pads.

摘要

Compost pads are frequently constructed employing open windrows over a porous sand and crusher-run aggregate surface supported by compacted finer textured subsoil with limited infiltration capacity. A MatLab-SimulinkReg. compartmental dynamic model was developed with the goal of linearizing the system and developing an instantaneous rainfall-runoff unit hydrograph. The MatLab-Simulink model was verified with a HYDRUS 2DReg. model before developing the unit hydrograph. Infiltration rate and percolation through the crusher-run media were measured using double ring infiltrometers. We compared the containment pond stage predictions from the HYDRUS and Matlab-Simulink compartmental models to the observed pond stage and found R2 values greater than 0.9, Nash-Sutcliffe statistics greater than 0.9, and Root-mean-square-errors (RMSE) less than 1% of the full pond volume on 16 storms occurring from (23 December 2010 to 21 June 2011). A continuous simulation over the calibration period (23 Dec. 2010 to 30 Jan. 2011) revealed good agreement of Matlab-Simulink and observed pond volume. Running the simulation between 10 April 2012 and 21 June 2011 suggested that an unmodeled compost absorption effect might be significant particularly in the summer period, along with evaporation and seepage losses. The Matlab-Simulink compartment model appeared to capture the physical runoff process occurring on the pad, except for the impact of the compost material itself. A transfer function for each linearized model made possible the determination of the impulse response at several linearized conditions. The instantaneous unit hydrograph is the impulse response at the appropriate linearization. From these analyses, we proposed an instantaneous unit hydrograph for similarly constructed windrow compost pads and believe the approach to be relevant to any site where surface and subsurface flow processes are reasonably well defined.