A METHOD OF MODELING VERTICAL FLUID-FLOW AND SOLUTE TRANSPORT IN A GIS CONTEXT

An irrigated agricultural area of 2350 ha in the San Joaquin Valley of California was used for assessing regional-scale vertical flow and so lute transport. The study area was sufficiently large to show variabil ity in salt-loading to the groundwater due to cropping and irrigation efficiency. A geographic information system (GIS) was used to store an d manipulate a variety of data required for vertical transport modelin g of water flow in the field area. Measured data included crop and irr igation schedules, daily evapotranspiration, soil type maps, and field sampling for determination of physical properties such as the saturat ion percentage and the gravimetric water content. A data classificatio n scheme was developed consisting of four basic types of variables: (1 ) local variables for point data; (2) spatial variables for data havin g a constant value within a restricted domain such as an individual qu arter-section; (3) derived variables being those selected based on a d iscrete value of another parameter (e.g. maximum root depth depends on the discrete variable, crop type), and (4) regional variables exhibit ing a constant value over the entire study area. Each specific Variabl e 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 sele cted locations by a capacity-based, one-dimensional transport model. T he results of a calculation were incorporated into the database for fu rther manipulation and representation. A sample calculation was run fo r 315 locations within the field area to determine the spatial variati on of salt-loading to the groundwater.