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INTRODUCTION: In the late 1970's and early 1980's, the Missouri Basin States Association conducted a hydrology study to evaluate historic and future availability and use of water in the Missouri River Basin. The study established a Ground Water Depletion Work Group with a primary study objective to select, and modify as needed, a technique for analyzing streamflow depletions due to ground water pumpage. The results of the investigations conducted by the Ground Water Depletion Work Group are published in "Technical Paper Ground Water Depletion"; (Missouri Basin States Association, 1982). As part of that study transmissivity and stream depletion factor maps of the Platte River basin in Colorado, Nebraska, and Wyoming were developed and published as Appendix II of the report, but under separate cover. These maps can provide useful information to those working on various aspects of hydrology in the Platte River basin. To provide greater access to these maps and because these maps have been out of print for some time and a re now difficult to find, it was decided to make them part of the coverages available in the geographical information system. The original ground water depletion work was conducted by individuals representing several State and Federal agencies. The following is a list of work group members. Clarence Bueltel, Work Group Chairman Missouri River Basin Commission Robert Keasling, Vice Chairman U.S. Army Corps of Engineers Richard Kern, Vice Chairman Nebraska Natural Resources Commission Robert G. Horner, Staff Coordinator Missouri River Basin Commission |
Work Group Members and Participants |
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Caralee Chaney Montana Dept. of Natural Resources and Conservation Darrell Ewing U.S. Bureau of Reclamation Lower Missouri Region Dale Frink North Dakota State Water Commission Rick Gold U. S. Bureau of Reclamation Upper Missouri Region Donald R. Hammer Missouri Dept. of Natural Resources John A. Henderson and Ron Balsters Kansas Water Office Dan Law Colorado Conservation Board |
John Overing USDA - Soil Conservation Service Marvene Riis and Randy Hilding South Dakota Dept. of Natural Resources Hal Simpson Colorado Division of Water Dick Stockdale Wyoming State Engineer's Office O.J. Taylor U.S. Geological Survey Dr. Tsong C. Wei U.S. Army - Corps of Engineers Jim Wiegand Iowa Natural Resources Council |
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The following discussion was copied from the original report (Missouri Basin
States Association, 1982) in order to provide some background on the construction
of the maps. For a thorough understanding of map construction, it would be best to
review the original document.
DEFINITIONS Transmissivity -- is the rate at which water is transmitted through a unit width of the aquifer under a unit hydraulic gradient. It is equal to the hydraulic conductivity multiplied by the thickness of the zone of saturation. It is expressed as gallons per day per foot. Stream depletion -- is either a direct depletion of the stream or reduction of ground water flow to the stream as a result of pumping a well in units of acre-feet. Stream Depletion Factor (SDF) -- defined as 
, which has a dimension of time with "a" the distance from the well to the
stream in feet, "S" the specific yield, and "T"; the transmissivity.
The SDF has a unit of time and is the result of analyzing aquifer properties such as
transmissivity, specific yield, and well location. When the well is pumped continuously
and when the volume of stream depletion reaches 28 percent of the total volume pumped,
the pumping time would be approximately equal to one SDF at the well (Jenkins, 1968).
MAPSSelection of the proper type of map and a workable scale were important elements in the study. The county Road Map with a scale of 0.5 inches = 1 mile was selected. These maps are readily available from the various State Highway Commission offices. The small amount of distortion noted in matching the counties within a State and also in matching maps between two States did not have an effect on the computational results. TRANSMISSIVITY DATA Transmissivity data was obtained from the U.S. Geological Survey (USGS), State Geological Survey, State Conservation and Survey Divisions and State Engineer Offices. The work group encountered problems in matching transmissivity data at State lines. A brief discussion of how and where the data were obtained and also on problems incurred in matching data follows, by State: Colorado Transmissivity and stream depletion Factor maps were obtained from a series of six open-file reports published by the USGS in 1972, "Hydrogeologic Characteristics of the Valley-Fill Aquifer in the South Platte River Valley" (Hurr and Schneider, 1972 and 1973a - 1973e). The maps covered the South Platte River area from Denver to the Colorado-Nebraska State line and were plotted on a scale of 1 inch = 1 mile. The State Engineer's office, supplied transmissivity information on the Cache la Poudre, St. Vrain and Big Thompson streams. It was developed from registered well log data and saturated aquifer thickness maps. Wyoming The transmissivity map for the North Platte River in Goshen County, Wyoming, was obtained from a report of the U.S. Geological Survey in Cheyenne, Wyoming, titled, "Hydrologic analysis if the Valley-fill aquifer, North Platte River Valley, Goshen County, Wyoming" (Crist, 1975). Early in the ground water study, it was found that transmissivity maps did not match for the North Platte River at the Wyoming-Nebraska State line. In order to rectify the situation, the vice-chairman of the Ground Water Depletion Work Group, met with U.S. Geological Survey and Nebraska Conservation and Survey Division representatives. A decision to draw a new transmissivity map was reached at a meeting in June 1980. The Conservation and Survey representatives indicated that a transmissivity map could be drawn which would better fit the Wyoming map. The new map would be based on data obtained from registered irrigation well data. The following equation permits the transmissivity calculation from the well data (Hunton, 1974).  where: T = Transmissivity in gpd/ft Q = well yield in gpm S = drawdown or difference, in feet, between the static and pumping water levels Transmissivities of wells near the North Platte River were plotted on a map and contoured. Areas of zero transmissivity were found in Scottsbluff, Morrill, and Garden Counties and used as the boundary. Many of the wells on the other side of these zero areas are in the Brule formation and are not hydraulically connected to the North Platte River. These wells were excluded from the study. The SDF technique does not model wells beyond an impermeable boundary. The new transmissivity map was reviewed by the Ground Water Work Group and a representative from Nebraska. After some changes in Garden County, a final agreement was reached. No changes were made in the Wyoming information, since the data revised for Nebraska allowed the joining of transmissivity lines. Nebraska Transmissivity maps for the Platte River basin in Nebraska were obtained from the U.S. Geological Survey office in Lincoln, Nebraska. These maps had been developed previously by the USGS, and the Conservation and Survey Division of the University of Nebraska for the Platte River Basin Level B report (Missouri River Basin Commission, 1976). The Conservation and Survey Division furnished information for the Republican River system. They had previously developed the data for the Ogallala Aquifer High Plains Study. Variability in the transmissivity information on the South PLatte River at the Colorado-Nebraska State line was minimal and therefore it was possible to join the contour lines for transmissivity. REFERENCES Crist, M.A., 1975, Hydrologic analysis of the valley-fill aquifer, North Platte River Valley, Goshen County, Wyoming: U.S. Geological Survey Water-Resources Investigation 3-75, 60 p. Hunton, P. W., 1974, Predicted water level declines for alternative groundwater developments in the Upper Big Blue River Basin, Nebraska: University of Nebraska, Conservation and Survey Division Resources Report 6. Hurr, R.T., and Schneider, P.A., 1972, Hydrogeologic characteristics of the valley fill aquifer South Platte River Valley, Colorado: U.S. Geological Survey Open-file Report. Jenkins, C.T., 1968, Technique for computing rate and volume of stream depletion by wells: Ground Water, 2, March-April. Missouri Basin States Association, 1982, Technical Paper Ground Water Depletion: Missouri River bain Hydrology Study, 2 vol. Missouri River Basin Commission, 1976, Report on the Platte River Basin, Nebraska, Level B Study, 1 vol. |
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