Hydrology of the Crow Reservation

This page was written by Erin Klauk and Linda Lennon as part of the DLESE Community Services Project: Integrating Research in Education. Funding was provided in part by the Montana Office of Public Instruction.

View of Little Bighorn River from Last Stand Hill at Little Bighorn Battlefield National Monument. Details

Recharge to the aquifers on the Crow reservation is mainly from infiltration of precipitation and streams. A smaller amount of recharge occurs by subsurface in-flow from outside the reservation, by infiltration from stock ponds and reservoirs where they have been constructed on outcrops, and from leakage across confining beds. Discharge from aquifers on the reservation is by evapotranspiration in outcrop areas and along the stream valleys, by springs and seeps, and by wells. Discharge also occurs by interformational leakage and by subsurface outflow from aquifers along boundaries of the outcrop area. The quality of water or the types and amounts of minerals dissolved in water depend on the chemicals and physical characteristics of the soil and rocks over or through which the water passes, the length of time the water is in contact with the soil and rocks, and other factors such as temperature and pressure (Crow Indian Tribe: Hydrology Resources Report).

Coalbed methane is natural gas trapped in underground coal deposits that also store thousands of gallons of water. Coalbed methane extraction requires that the coal seams be drained of water, emptying aquifers that may take hundreds of years to refill (Wyoming Coalbed Methane Leases Ruled Illegal (more info) ). In the Powder River Basin, the average coalbed methane well discharges 15,000 to 20,000 gallons of salty water per day, impacting surface soils, vegetation and aquatic animals. The BLM predicts that exploiting some 80,000 coalbed methane wells in Wyoming and Montana will discharge at least four trillion gallons of water over the next 15 years (Wyoming Coalbed Methane Leases Ruled Illegal (more info) ). Each coal deposit is different, so the amount of water that must be pumped to the surface varies. The amount of water also varies over the life of the well, with more water being removed from the coal seam initially, and then declining over time. For more information about the quantity and quality of water removed from coal seams in the Powder River Basin, refer to this United States Geological Survey report (more info) .

Water monitering on the Powder River in Montana.
Water monitering on the Powder River in Montana. Details

The composition of the water removed during coalbed methane production varies, even within coal deposits. For example, a USGS monitoring project in the Powder River Basin shows an increase in dissolved sodium (Na+) and bicarbonate (HCO3), along with an increase in total dissolved solids. In general water produced from coal seams can be saline (contains a high concentration of dissolved salts), or sodic (high in sodium concentration relative to concentrations of calcium and magnesium), or both.

  • To learn more about the saline and sodic chemistry of coalbed methane co-produced water in Montana's Powder River Basin, click here (more info) .
  • To learn more about why salt water is a constant threat to irrigated agriculture, click here (more info) .
  • To learn more about the USGS's water composition and monitoring efforts underway in the Powder River Basin click here (more info) .

Local aquifers may or may not be affected by water extraction, depending on the local geology, but there is usually some drawdown measured. Various agencies now monitor water in the affected areas to learn more about this process. For more information about potential drawdown in the aquifer of Wyoming's Powder River Basin, refer to this US Bureau of Land Management report (more info) .

There are many possibilities of what is done with the water generated during coalbed methane production, depending on water composition. The water can be released on the surface and used to irrigate crops or water livestock if it is clean enough. There is some disagreement about what is clean enough, however. Water extracted from coal seams can negatively affect soil, crops and native plants. For example, using saline water for irrigation can eventually inhibit germination and plant growth. Excess sodium can change the physical properties of soil, leading to poor drainage and crusting. This in turn can affect both plant growth rates and crop yield. Other alternatives, such as re-injection, can be costly. Water rights relating to coalbed methane production can be contentious in the arid west, and to a degree remain unresolved.

Little Bighorn Tribal College students and Crow Fish and Wildlife Department employees participate in field training regarding riparian habitat improvements on the Little Bighorn river.
Little Bighorn Tribal College students and Crow Fish and Wildlife Department employees participate in field training regarding riparian habitat improvements on the Little Bighorn river. Details

To further investigate the hydrology of the Crow Reservation, follow the links below.

Hydrology of the Crow Reservation

Resources containing information about the hydrology on the Crow Reservation.

  • Beneficial Use Alternatives. This 160-page PDF document is a chapter from a book on coalbed methane (CBM). This chapter identifies and discusses traditional technologies along with new or innovative applications of existing technologies that may allow for the beneficial use of CBM produced water. Beneficial use alternatives are categorized into six beneficial use groups: underground injection, impoundments, surface discharge, agricultural, industrial, and domestic and municipal use. Tables, diagrams and maps accompany the text. (more info)
  • Coal-bed Methane Gas Development in Montana, Some Biological Issues. This 11-page Department of Environmental Quality report discusses biological issues that are expected to occur from coalbed methane development in Montana. These issues include dewatering of local and regional aquifers; decreased surface water availability in some areas; increased surface water flows in areas receiving CBM discharges in other areas; water quality effects of CBM development discharges on waters and biota receiving the CBM discharges; and creation of significant surface disturbances from CBM facility and service road construction. (more info)
  • Crow Indian Tribe: Hydrology Resources Report. This 12-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section thoroughly describes the hydrology of the Crow Reservation. Included are maps illustrating the hydrologic basin, groundwater, wells and springs, and both water and coalbed methane wells. Also included are detailed tables of the rivers, streams, and tributaries within the Crow Reservation. ( This site is likely no longer available. )
  • Frequently Asked Questions: Coal Bed Methane (CBM) . This resource from Montana State University includes information about coalbed methane, such as what it is, where it is found, and how the resource is developed. (more info)
  • Hydrology Appendix. This 40-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section is a hydrology appendix for the Crow Reservation. Included is a summary of the water resources technical report, which provides information pertaining to groundwater quality and quantity, surface water quality and availability, produced water management, water conservation, water rights, and groundwater resource assessment as they relate to coal bed methane development. (more info)
  • Potential Groundwater Drawdown and Recovery from Coalbed Methane Development in the Powder River Basin, Montana. This 58-page PDF document from the US Bureau of Land Management assesses the potential impacts of coalbed methane development on water resources in Montana's Powder River Basin. The study explores the regional hydrogeologic setting, as well as using computer modeling to forecast anticipated impacts to the local groundwater and surface water resources. Groundwater issues addressed include reduction in hydrostatic head in coal aquifers, quantities of produced water and disposal options, impacts to alluvial aquifers and ground-water recovery potential. Maps, tables, hydrograms and 10-year and 20-year projections are also included. (more info)
  • U.S. Geological Survey Monitoring of Powder River Basin Stream-Water Quantity and Quality. This USGS report documents the ongoing monitoring of streams in the Powder River Basin. This report summarizes some of the available monitoring data and data relations that may be useful for assessing water-quality changes that coal bed methane discharges may have on surface water quality. In addition to the available data, the report discusses streamflow characteristics, increases in stream specific conductance over time, and relations between specific conductance and sodium-adsorption ratios. (more info)
  • Water Co-produced with Coalbed Methane in the Powder River Basin, Wyoming: Preliminary Compositional Data. This 20-page USGS report from preliminary data focuses on water that is produced with the development of coalbed methane in the Power River Basin. To accompany the text, many figures and tables are included. (more info)
  • Water Produced with Coal-Bed Methane. This 2-page PDF from the USGS provides information about water produced with coalbed methane. Topics include volumes and compositions of CBM water, fate of CBM water, USGS studies of CBM produced water. Tables and figures accompany the text. (more info)
  • Water co-produced with coalbed methane in the Powder River Basin, Wyoming: preliminary compositional data . This USGS open-file report provides preliminary compositional data on water from 47 coalbed methane wells sampled between June, 1999 and May, 2000 in the Powder River Basin, Wyoming. Results include data on major, minor and trace elements. The report also describes the geological setting of the basin with a stratigraphic column, a cross section and a geologic map. (more info)

For ideas on how to use these webpages in a classroom, a Study Guide is provided.