Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2002
Publication Date: July 27, 2002
Citation: RAWLS, W.J., PACHEPSKY, Y.A. USE OF SOIL SURVEY INFORMATION FOR DETERMINING SOIL HYDRAULIC PARAMETERS FOR HYDROLOGIC MODELING. FEDERAL INTERAGENCY HYDROLOGIC MODELING CONFERENCE. 2002. Technical Abstract: The soil controls the downward movement of water in the subsurface and the amount of water available for evapotranspiration. Knowledge of soil physical and hydraulic properties is, therefore, a key element in hydrologic modeling. Laboratory and field methods for determining soil hydraulic properties are time consuming and expensive. Average soil hydraulic properties developed in the early 1980's according to soil texture are commonly used in models; however, pedotransfer functions which are basically procedures to relate basic soil properties such as texture, organic matter, bulk density, etc to properties that are rarely measured on a routine basis such as soil-water retention and saturated/unsaturated hydraulic conductivity are now readily available. Pedotransfer functions (PTF's) which predict various soil hydraulic properties (water retention and hydraulic conductivity) based on various levels of soils information were developed by applying regression, regression trees, and abductive network techniques to the NRCS national soils data base. The qualitative information used in the pedotransfer functions were USDA soil texture classes, structure, grade, size and shape classes, dry and moist consistency classes and stickness and plasticity classes which are reliably estimated in the field and are part of every soils description and the quantitative soils information were measured particle sizes, bulk density, shrink-swell potential, organic matter, coarse fragments and water retention at one or more potentials. Pedotransfer functions are presented for the following levels of information (1) qualitative data from soil survey; (2) Ranges of physical properties from STATSCO; (3) combination of qualitative class data with measured physical properties: (4) measured soil physical properties; and (5) measured soil physical properties with one or more measured water retention value.