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Show 4 . VALENTIMES - FEBRUARY 1993 SPRINGS NORTHEAST CASTLE CREEK WATER TABLE 2% Castle Valley Ground i Water 1 -—\ “.— _‘—._ —' ‘ CLAY Eml l —/ / /' \-— SALT BEARING ROCKS / SAND. GRAVEL. AND BOULDERS EEDROCK (YOUNGER THAN SALT) LEY SECTION ACROSS LOWER CASTLE VAL Understanding the water resources and clay, as well as the underlying of Castle Valley, particularly the ground water resource, requires a little knowledge of the geology of the valley. A good idea of what underlies Castle Valley can be obtained by driving a older rock, are saturated with water. few miles to the northeast and turning water to flow. The measure of the ability of a material to allow water to flow through it is called permeability. The greater the permeability the faster up Onion Creek to Fisher Valley. Both Fisher Valley and the valley through which Onion Creek flows are collapsed salt structures similar to Castle Valley. Along Onion Creek can be seen examples of the complex of rocks that underlie Castle Valley. As the road climbs out of the Onion Creek drainage onto the floor of Fisher Valley, in the cliff face we can see the younger valley-fill sediments composed of sand, gravel, clay, and boulders that overlie the older rocks and form the floor of Fisher Valley. These sediments are debris washed into the valley from the adjoining highlands. A similar complex mixture of sand, gravel, boulders, and clay forms the floor of Castle Valley. In CastleValley these sediments are up to 500 feet thick and contain the ground water that is produced fiom most of the wells in the valley. Below a relatively shallow depth in Castle valley all of this sand, gravel, However, water can move from this saturated material into a well only if the spaces containing the water are interconnected in a way that allows the water will flow through the material. Gravel and sand have high permeability, sandstone intermediate, and clay and shale low permeability. Water can also be produced from open fractures in rock. The geologic units that contain and will produce water are called aquifers. If a gravel or sand aquifer is enclosed between layers of clay, the aquifer is confined and the water may be under pressure much as water is in a pipe. Some of the ground water tapped in Castle Valley today fell as precipitation directly in the valley, but more fell as precipitation on the La Sal Mountains and then flowed on the surface or through the subsurface into Castle Valley. The water table in Castle Valley is a relatively regular surface rising gradually from the approximate elevation of Castle Creek in the lower part of the valley toward the margins of the valley and rising up the valley less rapidly than the creek bed. The surface water that flows in Castle Creek and the smaller intermittent drainages and the ground water underlying the valley are related. Major actions affecting one will likely affect the other. In the upper part of Castle Valley, Castle Creek looses water through the stream bed into the ground water aquifer. In the lower part of the valley, groundwater flows from the shallow aquifer into Castle Creek at numerous springs. Movement of water through the ground is controlled by the same physical laws as water movement on the surface. Water flows downhill, the velocity of flow is faster down a steep slope, obstructions reduce the velocity of flow, and water in a pipe or a confined aquifer flows in response to pressure differences. A water budget can be developed for a drainage basin such as Castle Valley and the areas of the La Sal Mountains that drain into the valley. This involves determining: (1) the input as the average yearly volume of precipitation that falls over the basin, (2) the output as the volume of water that flows as surface and ground water from the basin, (3) the volume of water lost through evaporation and transpiration (from plants), and (4) the volume Castle Valley Inn For the best rent out west. A’Bed and Breakfast Eric Thomson & Lynn Forbes Thomson 801-259-6012 CVSR 2602, Moab, Utah 84532 of available ground water in storage. Such a budget can be used to determine the amount of water available for development and the impact of different development scenarios. Data to support the development of a water budget are being collected in Castle Valley. —Don Mabey NEXT MONTH, GROUND WATER QUALITY AND PROTECTING AND DEVELOPING GROUND WATER. |
