Model for evaluating the effects of dikes on the water and salt balance of Great Salt Lake, Utah

Abstract

A model was developed for predicting the water and salt budget for various diking options in Great Salt Lake. The water budget was computed for 1-month intervals during a base period of 1931-73. The storage change (AS) during each month of the base period was computed from a budget of surface inflow (Is), groundwater inflow (Ig), precipitation on the lake surface (Ip), and outflow from evaporation (Oe), where AS = Is + Ig +Ip - Oe. The total annual inflow to Great Salt Lake ranged from about 1.5 to 5 million acre-feet (1,849.5 to 6,165.0 cubic hectometres). The Bear River contributes the largest percentage of the measured surface inflow. The total annual outflow from the lake (evaporation) ranged from about 2.2 to 4.0 million acre-feet (2,712.6 to 4,932.0 cubic hectometres) during 1931-73. The average annual evaporation was 2.98 million acrefeet (3,674.3 cubic hectometres) or 45 inches (1,143 millimetres) per year. The model provides for nine diking options. These include combinations of eight areas east of a line joining Antelope Island, Fremont Island, and the Promontory Mountains. Another option includes the part of Great Salt Lake that lies north of the Southern Pacific Transportation Co. causeway, which divides the main body of the lake into north and south parts. The model treats the salt balance of the diked areas from the standpoint of an inflow-outflow balance with complete mixing, and no allowances are made for any stratification or chemical changes due to interaction with the sediments or solution of entrapped brines or residual salts. Because the degree of inaccuracy created by these assumptions is not known, the concentrations predicted by the model should be regarded not as absolute but as relative indexes by which to compare various diking alternatives.