River basin hydrosalinity modeling
ABSTRACT Tanji, K.K., (1981). River basin hydrosalinity modeling. Agric. Water Manage., 1981. Hydrologic-salinity modeling at the river sub-basin and basin spatial scales in the Western U.S.A. are evaluated. In the past two decades, significant advances have been made in basin hydrosalinity modeling. These models are providing increased understanding of the complexity of water and salt flows in large-scale systems. Most models, however, have been developed for specific problems and do not lend themselves for application to a wide variety of salinity problems. Much more work is needed in the areas of field verification of models and increasing their utility for management and policy-making decisions.
A Computer Model of the Quantity and Chemical Quality of Return Flow
A hybrid computer program is developed to predict the water and salt outflow from a river basin in which irrigation is the major water user. A chemical model which predicts the quality of water percolated through a soil profile is combined with a general hydrologic model to form the system simulation model. The chemical model considers the reactions that occur in the soil, including the exchange of calcium, magnesium, and sodium cations on the soil complex, and the dissolution and precipitation of gypsum and lime. The chemical composition of the outflow is a function of these chemical processes within the soil, plus the blending of undiverted inflows, evaporation, transpiration, and the mixing of subsurface return flows with groundwater. The six common ions of western waters, namely calcium (Ca ++ ), magnesium (Mg ++), sodium (Na +), sulfate (S04= ),chloride (Cl-), and bicarbonate (HC03) are considered in the study. Total dissolved solids (TDS) outflow is obtained by adding the individual ions. The overall model operates on monthly time increments. The model is tested on a portion of the Little Bear River Basin in northern Utah. The model successfully simulates measured outflows of water and each of the six ions for a 24-month period. Only sodium ions, which occurred in small concentrations comprising approximately 2 percent of the total salt outflow, exhibit significant discrepancies between predicted and observed values. All other ions agree within 10 percent on a weight basis for the two-year model period, with correlation coefficients ranging from .87 to .97. The usefulness of the model is demonstrated by a management study of the prototype system. For example, preliminary results indicated that the available water supply could be used to irrigate additional land without unduly increasing the salt outflow from the basin. With minor adjustments the model can be applied to other areas. Thomas, Jimmie L.; Riley, J. Paul; and Israelsen, Eugene K. A COMPUTER MODEL OF THE QUANTITY AND CHEMICAL QUALITY OF RETURN FLOW. Research Project Technical Completion Report to the Office of Water Resources Research, Department of the Interior, Washington, D.C. June 1971,94 p. KEYWORDS--water pollution sources/*ion exchange model/*water quality model/*irngation return flow/hydrology/ hydrologic models/ simulation/*groundwater/*groundwater quality/ water resolVces planning and management/hybrid computer/deep percolation /*hydrologicquality models
MISCIBLE DISPLACEMENT IN SOILS: I. EXPERIMENTAL INFORMATION
When a fluid containing a tracer in solution is displaced from a porous medium by the same fluid without a tracer, this miscible displacement results in a tracer concentration distribution which depends upon microscopic flow velocities, tracer diffusion rates and other chemical and physical processes. Miscible displacement has been studied in several porous materials under saturated and unsaturated conditions at different average flow velocities. The tracer appeared at the end of the soil column well in advance of that expected had no mixing occurred at the boundary of the tracer and tracer-free water. Physical differences between porous materials were manifested by changes in shape and position of breakthrough curves owing to ionic diffusion. One of the more important physical features was the magnitude of the volume of water not readily displaced at saturation and its increase when the soil was desaturated. Because the total flux of water moving through field soils is generally small, the role played by hydrodynamic dispersion and diffusion in transporting dissolved solutes must be included in the theory of most soilwater processes. View complete article To view this complete article, insert Disc 2 then click button8