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RISKPRO'S SESOIL for Windows User's Guide <br /> 3.3.3 Hydrologic Model Calibration <br /> Calibration of unsaturated soil zone models can be uncertain and difficult because climate, soil <br /> moisture, soil infiltration and percolation are strongly interrelated parameters that are difficult <br /> and expensive to measure in the field. However, if at all possible, input parameters for any <br /> unsaturated soil zone model should be calibrated so that hydrologic predictions agree with <br /> Iobservations In SESOIL, all input parameters required for the hydrologic cycle can be <br /> estimated from field studies with the exception of the pore disconnectedness index, "c". This <br /> parameter is defined as the exponent relating the "wetting" or "drying" time-dependent <br /> permeability of a soil to its saturated permeability (Eagleson, 1978, Eagleson and Tellers, 1982) <br /> Brooks and Corey (1966) presented the following relationship- <br /> K S = K 1 S (5) <br /> I <br /> where <br /> K(1) = saturated hydraulic conductivity (cm/s) <br /> K(S) = hydraulic conductivity at S (cm/s) <br /> S = percent saturation <br /> c = pore disconnectedness index <br /> i <br /> I <br /> I Thus, this parameter is not commonly found in most literature. Default values for "c" suggested <br /> by Eagleson (1978) and Bonazountas and Wagner (1981, 1984) are- clay 12; silty clay loam 10, <br /> clay loam 7 5, silt loam 5 5, sandy loam 6, sandy clay loam 4, and sand 3 7 However, when <br /> I data are available, this parameter should be vaned first to optimize agreement between SESOIL <br /> results and hydrologic measurements It should be noted that most unsaturated soil zone models <br /> require detailed data (which are difficult to obtain), such as soil moisture characteristic curves. <br /> IThe "one variable" approach of Eagleson (1978) simplifies the data estimation process and <br /> reduces computational time <br /> IOther sensitive parameters for the hydrologic cycle are the effective porosity and the intnnsic <br /> permeability (e g , see Hetnck et al , 1986, 1989) While other parameters can be vaned when <br /> I calibrating the model to measured hydrologic data, it is recommended that the user vary the <br /> disconnectedness index first, followed by the permeability and/or porosity See the section on <br /> input data for further details <br /> IPage 13 <br />