A method of modeling vertical fluid flow and solute transport in a GIS context

Abstract

An irrigated agricultural area of 2350 ha in the San Joaquin Valley of California was used for assessing regional-scale vertical flow and solute transport. The study area was sufficiently large to show variability in salt-loading to the groundwater due to cropping and irrigation efficiency. A geographic information system (GIS) was used to store and manipulate a variety of data required for vertical transport modeling of water flow in the field area. Measured data included crop and irrigation schedules, daily evapotranspiration, soil type maps, and field sampling for determination of physical properties such as the saturation percentage and the gravimetric water content. A data classification scheme was developed consisting of four basic types of variables: (1) local variables for point data; (2) spatial variables for data having a constant value within a restricted domain such as an individual quarter-section; (3) derived variables being those selected based on a discrete value of another parameter (e.g. maximum root depth depends on the discrete variable, crop type), and (4) regional variables exhibiting a constant value over the entire study area. Each specific variable was classified utilizing the classification scheme and a relational database was created for all the data. From the data included in this database, calculations of fluid and solute transport were made at selected locations by a capacity-based, one-dimensional transport model. The results of a calculation were incorporated into the database for further manipulation and representation. A sample calculation was run for 315 locations within the field area to determine the spatial variation of salt-loading to the groundwater.