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Show With the lake divided into distinct areas by the construction of causeways, the water and salinity balance for the entire lake is quite complex. The potential evaporation rate is different in each area due to differences in salinities. The spatial variation of inflows and the rate of flow through the causeways influence the surface elevation and salinity of each of the areas. Under present conditions the surface elevation of the south arm is always greater than the north arm while the north arm is more saline than the south arm. The components of the water balance must be understood and predictable under various lake conditions to provide the foresight necessary to enable predictions of how alterations of the present physical system will affect future lake levels. Because of the close tie between the water and salinity balance an understanding of the water balance is necessary in predicting future lake salinity trends. The converse of this is true when dealing with major divisions of the lake such as the north and south arms. The water balance for either arm of the lake is composed of the inflow and outflow to the lake and the exchange of brine between the two arms through the causeway. Flow through the causeway is a function of both the surface elevation difference across the causeway ( water balance) and the difference in salinity ( salt balance). Evaporation, perhaps because it is the only outflow from Great Salt Lake, has been the subject of a number of studies. In 1932, T. C. Adams established a method of estimating the evaporation from the Great Salt Lake by correlating pan evaporation of salt and fresh water. The work done by Adams has been referred to in most of the subsequent studies of evaporation from Great Salt Lake. Harbeck ( 1955) investigated the effect of salinity on evaporation from a theoretical basis and used the results obtained by Adams to verify his findings. Dickson, Yepsen, and Hales ( 1961) performed laboratory measurements of the vapor pressure of Great Salt Lake brine at various concentrations and temperatures. Dickson ( 1962) and Dickson and McCullom ( 1965) used vapor pressure, wind speed, temperature, and humidity data collected in the vicinity of Great Salt Lake to estimate evaporation using the eddy flux technique. Their results indicated evaporation from Great Salt Lake was greater than predicted in earlier studies. The main limitation of using these methods is that sufficient evaporation data are not available from the lake for verification. The U. S. Geological Survey ( USGS) is gathering basic data on evaporation at six stations around the lake which should help fill this void. As part of the same project, the USGS is also gathering basic data on surface inflows, precipitation, and radiation. This data gathering project is scheduled to end in September of 1976 to 1977. Precipitation, surface inflows, and groundwater infiows are inputs to the lake. Precipitation on the surface constitutes a major inflow to the lake. Except for the current USGS data gathering project, research on the distribution of precipitation over the lake at this time has not progressed much beyond the preparation of isohyetal maps, by E. L. Peck, which include the Great Salt Lake regions. The contribution which condensation of fog makes to the water budget has not been studied. The USGS has a program of monitoring the quality and quantity of flow in the major streams in the state. In their project mentioned above, the monitoring program has been expanded to measure the quality and quantity of major surface inflows nearer the lake and the miscellaneous flows which were previously ungaged. Before Farmington Bay was separated from the south arm by the Antelope Island causeway, the south arm directly received over 95 percent of the surface inflow to the lake. Thus, the major inflows to the north arm are precipitation and south arm brines. This inflow pattern has created a head difference across the causeway, with the south arm elevation being greater than the north arm. The Antelope Island causeway affects the flow of the Jordan River into the south arm. A culvert was constructed in the causeway to allow for flow between the bay and the south arm, but any impact this may produce on the hydrology of the south arm, is not yet known. The contribution which groundwater makes to the inflow to Great Salt Lake has not been well established. Lofgren ( 1954) estimates the groundwater inflow to be 30 percent of the total inflow. More recent investigators have placed the groundwater contribution at 6- 10 percent of the total annual inflow. Many of the estimates of total groundwater inflow to Great Salt Lake have come from water budget studies which are made by balancing inflow, outflow, and storage change in the lake. Major components in a water budget study of Great Salt Lake are evaporation and precipitation on the lake. The accuracy of estimating groundwater inflow using water budget studies are affected by the fact that neither evaporation nor precipitation on the lake is well defined. Groundwater conditions in Utah are investigated by the Utah Department of Natural Resources and the U. S. Geological Survey. Hely et al. ( 1971) discuss the groundwater conditions in Salt Lake County. Foote et al. ( 1971) use the data available 40 |