Estimating Vadose Zone Hydraulic Properties of Artificially Drained Fields Using Irrigation District and Soil Survey Data
Abstract
The prediction of water flow and solute transport through the vadose zone requires knowledge of the spatial distribution of soil hydraulic properties, such as the conductivity and retention parameters. Several point-scale techniques are available for measuring soil hydraulic properties. However, in applications at the field to regional scale, a prohibitively large number of sampling sites are needed to characterize the vadose zone. Therefore, an alternative approach is presented here, using readily available data. The method is applied to the estimation of the spatial distribution of soil hydraulic properties for a 4000 ha irrigation district located in the San Joaquin Valley, California, using two sources of data. First, the SSURGO soil survey dataset currently provides the most detailed information on the spatial distribution of soil types. Unfortunately, the data provided by the survey cannot directly be used in subsurface modeling efforts. Soil textural information from the survey must be converted to soil hydraulic parameters used by hydrologic models. Pedo-transfer functions are used to provide an estimated range for the soil hydraulic parameters based on the soil textural data in the soil survey. The second piece of data is available from the irrigation district and consists of irrigation applications, crop patterns, and tile drain flows at the field scale. These data are used to estimate soil hydraulic parameters by inverse modeling of tile drain flows with a variably saturated flow model and an efficient global optimization algorithm. This procedure consists of automatically adjusting soil hydraulic parameters until observed tile drain flows are reproduced. The parameter ranges estimated from the soil survey data and the pedo-transfer functions are used to constrain the parameter values in the optimization procedure.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.H31C0251S
- Keywords:
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- 1842 Irrigation;
- 1875 Unsaturated zone