Wyoming Framework Water Plan - Living Rivers Home Page

7.0 AVAILABILITY
River Basins. The Platte is home to all three of Wyoming’s Groundwater Control Areas – Prairie Center,
Platte County, and Laramie County – each precipitated by declining groundwater levels. See Figure 7-8.
It has also been the basin of groundwater interference complaints/investigations near Saratoga, Bates
Creek, Glenrock, Horseshoe Creek, Cottonwood Creek, Hawk Springs, and Laramie.
In the Powder River Basin, concerns with groundwater level declines are centered on the coalbed
methane (CBM) industry. CBM production is inherently in conflict with groundwater levels as it depends
on substantial drawdown to release the methane gas from the coal seams. For the same reason, CBM
development cannot occur where permeabilities are high, so it is an industry focused on areas where
groundwater supplies are not abundant to begin with. Short-term drawdowns in the Wasatch aquifer are
projected by the BLM EIS to be 500-800 feet over much of the basin. Recovered water levels following
CBM exhaustion are projected to remain 30 feet below original levels.
As CBM production spreads to other basins, it will target coal seams in the “sandstone” aquifers
shown on Figure 4-9. Impacts to existing groundwater users in these areas remain to be seen. Because
the coal seams are generally deeper than in the Powder River Basin, conflicts with existing users are
likely to be less.
No significant areas of groundwater decline are reported for the Bear, Snake/Salt, or Green River
Basins. In the Wind/Bighorn Basin, groundwater levels have dropped as a result of municipal and
irrigation withdrawals in the Riverton and Hyattville areas, respectively.
7.2.4 Groundwater Recharge
A common approach to estimating the quantity of groundwater available for continuous
development, as opposed to one-time extraction, is to estimate groundwater recharge. If no more water is
taken from the groundwater reservoir than flows into the reservoir, no long-term decline will occur. Total
groundwater recharge was estimated in several of the basin plans:
! 2 million ac-ft/yr for the Platte River Basin, based on recharge equal to 10 percent of
precipitation.
! 50,000 ac-ft/yr for the Green River Basin, based on recharge equal to 10 percent of precipitation,
but only for those areas where precipitation exceeds potential evapotranspiration.
! 1 million ac-ft/yr for the Snake/Salt River Basin, based on detailed estimates of recharge rates
from the University of Wyoming groundwater vulnerability study (Wyoming Water Resources
Center, 1998).
! 14,000 ac-ft/yr for the Bear River Basin, based on recharge equal to 2 percent of precipitation.
There is little consensus on detailed estimation of groundwater recharge rates, which are a
complex function of the seasonal timing, duration, intensity, and type of precipitation; the infiltration
characteristics of the soil; the hydraulic properties of the uppermost geologic materials; and the manner in
which groundwater recharge moves within and between aquifers. Groundwater recharge is the source of
“base flow” to streams. While matching groundwater consumption to recharge would prevent widespread
groundwater level declines, it would also lead to dry streambeds for much of the year.
Where groundwater is closely connected with surface water, as in much of the alluvial aquifers,
the locations and long-term availability of groundwater are effectively the same as for surface water.
There may still be good reasons to develop groundwater. A municipality, for example, may choose to
divert groundwater rather than the same quantity surface water, despite a depletive connection, to capture
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