Application of field infiltration data to hydrologic model parameterization : an example from drainage basins disturbed by surface mining

Abstract The sophistication and use of distributed hydrologic models are increasing at the expense of data collection and field experimentation upon which such models were conceptualized and parameterized. The purpose of this study is to explore the use of field data, collected from reclaimed surface mines, in the parameterization of ANSWERS, a distributed hydrologic model. A sensitivity analysis of ANSWERS was conducted at two scales, the plot scale ( 2 ), typically the scale at which field data are collected, and the drainage basin scale (0.1–0.3 km 2 ), the size of reclaimed surface mine basins. The results of this analysis indicate that at both plot and basin scale, the most sensitive parameter of the ANSWERS hydrologic model with respect to the volume and peak rate of hillslope runoff and basin discharge is steady-state infiltration capacity ( FC ), a variable that can be measured directly from a dripping-rainfall infiltrometer test. At the plot scale, the time to FC ( T fc ) is most sensitive to two parameters that control the rate of decay of the infiltration curve, namely, surface roughness ( RN ) and a dimensionless coefficient ( P ) relating infiltration capacity to soil moisture. By measuring FC from infiltrometer tests and adjusting RN and P by visually fitting simulated infiltration curves to field infiltrometer-derived infiltration curves, the ANSWERS model can be parameterized, in part, at the plot scale for hydrologic simulation at the basin scale. At the basin scale, the time to peak discharge ( T p ) of the simulated hydrograph is dependent primarily on accurate representation of the drainage network, a function of the element size selected to characterize the distribution of model parameters in the basin. Model performance was evaluated in two reclaimed surface mine basins, one dominated by infiltration-excess overland flow and the other by saturation overland flow. ANSWERS is most appropriately suited for drainage basins dominated by infiltration-excess overland flow because it is physically based with respect to infiltration, overland flow, and channelized flow processes. In these basins a field program of infiltrometer tests, designed to include representative basin surfaces with respect to soil and surface properties, is sufficient for model parameterization in order to supplement existing hydrologic data or to evaluate the probable hydrologic consequence of a land-use change. In drainage basins dominated by saturation overland flow, subsurface flow contribution to simulated hydrographs, described by the lumped parameter GRF, must presently be calibrated against observed storm hydrographs. Model parameterization is accomplished by augmenting the infiltration-excess component of the simulated hydrograph, determined by the above parameterization technique, with a specified proportion (GRF) of the infiltrated water. The lumped parameter GRF is problematic in the sense that it is sensitive to infiltration capacity as well as storm size and intensity and, therefore, must be calibrated for characteristic storm events. However, the ANSWERS model is recommended for further evaluation and use in surface mine environments, which are initially dominated by infiltration-excess overland flow due to low infiltration capacities of newly reclaimed mine soils.