Total groundwater resource in the Wind/Bighorn River Basin
One task of this study was to evaluate the available groundwater resource of the WBRB. An enormous quantity of groundwater is stored in the WBRB groundwater basins. However, in addition to the amount of water that an aquifer can sustainably yield, other factors must be considered in determining what part of total stored volume of groundwater may be considered a viable beneficial-use resource, including these:
- Groundwater must be of suitable quality for its intended use.
- The depth to the resource or other accessibility conditions must not preclude groundwater development because of high cost or technical infeasibility.
To address groundwater availability, we evaluate the available (potentially producible) WBRB groundwater resource by calculating:
- Groundwater stored and potentially recoverable within the upper 1,000 feet of the combined Quaternary/ Tertiary (Cenozoic) hydrogeologic units in the flatlying lower-elevation areas of the basins
- Groundwater stored and potentially recoverable within 10- and 20-foot thicknesses of all Quaternary hydrogeologic units exposed in the WBRB
- Average annual recharge (Figure 5-1) calculated over all hydrogeologic units exposed in the WBRB (Figures 6-3 – 6-6)
The methodology employed for estimating stored and available groundwater in the Q/T Aquifer, relatively flat-lying hydrogeologic units exposed within the lower-elevation interior areas of the WBRB (Figure 6-3), is similar to that used in the recently completed Available Groundwater Determination for the Greater Green River Basin Technical Memorandum (Clarey et al., 2010); in addition, we compare stored and available volume estimates with (average annual) recharge. Stored and available groundwater volumes and average annual recharge were also estimated for the Quaternary Aquifer (Figure 6-2), for saturated thicknesses of 10 and 20 feet. These estimates of the stored and available groundwater in the Quaternary and Q/T Aquifers neglect recharge and discharge.
For the combined Mesozoic/Paleozoic (Mz/Pz Aquifer) hydrogeologic units and the Precambrian ( Aquifer) hydrogeologic units (Figures 6-4 and 6-6), as well as the large area of Absaroka Volcanics that borders most of the western Bighorn Basin (Figure 6-5), groundwater resources were evaluated using only average annual recharge. The rationale for using different methodologies is that folding and faulting of the and Aquifers around the perimeters of the structural basins has affected the distribution and depth of useable groundwater and does not allow assumptions such as a general depth limit for groundwater development. Much of the Absaroka Volcanics terrain is inaccessible; and the highly eroded, complex to chaotic hydrogeologic framework likewise precludes assumptions that allow estimation of groundwater in storage.
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