Abstract

Studies of the ground-water basins of the Wasatch Front began in 1904 with reconnaissances by the U.S. Geological Survey, followed in 1931 by more detailed studies, mostly as part of a cooperative program between the U.S. Geological Survey and the Utah Division of Water Rights which continues to the present. These studies evolved from descriptions of the physical system and the status of ground-water development to quantification of the ground-water system of each basin using computer models, and can be classified as hydrogeologic, water-budget, and modeling studies. Ground water is an important part of the water supply of the Wasatch Front—in 1990, 21 percent of the water withdrawn was ground water, and ground water furnished 56 percent of water withdrawn for public supply/commercial use.

The basin-fill ground-water system is the primary source of ground water in the Wasatch Front area, and is made up of a shallow water-table zone in the lower parts of the basins, an underlying confined aquifer, and a deep unconfined aquifer along the mountain fronts, laterally equivalent to the confined aquifer. The confined and deep unconfined aquifers generally are together termed the “principal aquifer” in each basin.

Recharge to the system, and especially to the principal aquifer, mostly occurs along the mountain fronts by seepage from mountain streams and channel underflow, seepage from irrigated land and canals, infiltration of precipitation, and subsurface seepage from the consolidated rocks of the mountains. Discharge from the system includes natural discharge as seepage to streams, lakes, or reservoirs, by evapotranspiration, and from springs; and discharge caused by human activity—from wells and to drains. We commonly do not have detailed information on where and how recharge from most sources occurs and of the areal variations in most means of discharge.

Paths of movement from areas of recharge to the natural discharge area in basin lowlands can be inferred approximately from contours of potentiometric-surface maps. The maps indicate general basin-wide flow patterns; they are not adequate to define precise directions of flow in local areas. Shifts in contours on successive potentiometric-surface maps of the East Shore area, Salt Lake Valley, and northern Juab Valley reflect the effects of ground-water withdrawals.

Results of ground-water basin studies have been used by the State of Utah since the 1930’s to help solve water-right and appropriation problems, in preparing the State Water Plan, and to evaluate groundwater contamination problems. Defining the limit of ground-water development based on ground-water budget information may not be useful; limits probably are better defined by the hydrologic effects that can be tolerated. Models can be useful in estimating system-wide effects of proposed levels of development. Budgets are useful in defining the upper limit of natural discharge that can be captured to provide water for sustained withdrawals.

Successive studies of ground-water basins along the Wasatch Front have resulted in more complete and presumably more accurate estimates of ground-water budgets. Changes in estimates of total recharge and/or discharge generally have been 50 percent or less. Changes in individual major components of recharge or discharge have been as large as 100 percent. Considering the different methodologies used, differences in assumptions, and different time periods of estimates, the changes in estimates of total recharge and discharge are not large.