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Black Hills Hydrology Study
| Introduction|| Objectives|| Study Area|| Percipitation|| Digital Map Products|
The Black Hills area is a unique and valuable asset to the State of South Dakota. In addition to its historic landmarks, scenic beauty, timber, and mineral resources, the Black Hills area is a major source of water. Streams flowing from the Black Hills provide water for a multitude of uses in the Cheyenne and Belle Fourche River Basins. In addition, much of western South Dakota and parts of eastern Wyoming are underlain by bedrock aquifers that are recharged in the Black Hills area.
Water resources of the Black Hills area have been stressed by increasing population, resource development, and periodic droughts. Additional water supplies are being developed for rapidly expanding communities. The potential exists for water-quality degradation from mining activity, urbanization, irrigation, forest management activities, and recreational development. Drought conditions in the late 1980's caused reduced streamflow, declining reservoir and ground-water levels, and shortages of water supplies for domestic, municipal, industrial, agricultural, and recreational purposes.
The hydrogeology of the Black Hills area is very complex. Several regional, artesian bedrock aquifers and various local aquifers are exposed and recharged in the Black Hills area. The bedrock aquifers are separated by confining units, which are composed of less permeable rocks. The thickness and permeability of aquifers and confining units are known to change with location (Peter, 1985; Kyllonen and Peter, 1987; Greene, 1993). Numerous fractures, faults, and solution cavities allow flow of water in rocks that otherwise are relatively impermeable. This is especially true of the Madison Limestone, which is well known for its karst features, including sinkholes and water-loss zones in streams, collapse features, solution cavities, and caves. Surface- and ground-water resources are connected by water-loss zones in streams and by large springs originating from one or more aquifers. Development of ground-water resources may affect surface-water resources. Conversely, development or contamination of surface-water resources may affect ground water. Detailed hydrogeologic information is necessary for effective management of water resources in the Black Hills area.
To address the need for regional hydrogeologic information, the Black Hills Hydrology Study was initiated in 1990 as a long-term investigation designed to assess the quantity, quality, and distribution of surface- and ground-water resources of the Black Hills area. The study was completed in 2002. The Black Hills Hydrology Study was a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources (DENR), and the West Dakota Water Development District (West Dakota). West Dakota served as the primary local cooperating agency and represented various local and county cooperators. West Dakota was assisted in this capacity by a steering committee consisting of area residents and representatives of various local governmental agencies.
ObjectivesThe original study plan (Driscoll, 1992) set forth objectives for the entire study. Specific objectives of the Black Hills Hydrology Study were to:
The study area includes the topographically defined Black Hills and adjacent areas as shown in figure 1. The boundaries of the study area were modified slightly since publication of the original plan of study (Driscoll, 1992).
Figure 1. Area of investigation for the Black Hills Hydrology Study
The Black Hills are a dome-shaped uplift of Laramide age, about 125 miles long and 60 miles wide (Feldman and Heimlich, 1980). Altitudes range from about 7,200 feet at the higher peaks to about 3,000 feet in the surrounding plains, resulting in an orographically induced microclimate characterized by generally greater precipitation and lower temperatures at the higher altitudes. The overall climate of the area is continental, which is characterized generally by low precipitation amounts, hot summers, cold winters, and extreme variations in both precipitation and temperatures (Johnson, 1933). Long-term trends in precipitation for water years 1931-98 for the study area are shown in figure 2; a water year is the 12-month period, October 1 through September 30, and is designated by the calendar year in which it ends. Average annual precipitation for water years 1931-98 in the study area is 18.61 inches, and has ranged from 10.22 inches in water year 1936 to 27.39 inches in water year 1995 (Driscoll, Hamade, and Kenner, 2000). The average annual temperature is 43.9 degrees Fahrenheit, and ranges from 47.6 degrees at Hot Springs to approximately 37 degrees near Deerfield Reservoir (U.S. Department of Commerce, 1990).
Figure 2. Long-term trends in precipitation for water years 1931-98 for the study area
The oldest geologic units in the stratigraphic sequence are the Precambrian igneous and metamorphic rocks (fig. 3). The Precambrian rocks are exposed in the central core of the Black Hills, extending from near Lead to south of Custer (fig. 4). Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills (DeWitt and others, 1989). The outcrops of the hydrogeologic units and locations of numerous structural features (anticlines, synclines, domes, faults, and monoclines) are shown in figure 4. The bedrock sedimentary formations typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift (fig. 5).
Figure 3. Stratigraphic column for the Black Hills
Figure 4. Distribution of hydrogeoloic units
Figure 5. Geologic cross section
Many of the sedimentary formations commonly are used as aquifers, both within and beyond the study area. Recharge to these aquifers is from infiltration of precipitation on the outcrops and from stream infiltration along the flanks of the Black Hills (Peter, 1985; Kyllonen and Peter, 1987; Greene, 1993). Within the Paleozoic section, the Deadwood Formation, Madison Limestone, Minnelusa Formation, and Minnekahta Limestone commonly are used as aquifers. These aquifers are collectively confined by the underlying Precambrian rocks and the overlying Spearfish Formation. Individually the aquifers are separated by minor confining layers, or by relatively impermeable layers within the individual formations. Leakance between the aquifers is extremely variable (Peter, 1985; Greene, 1993). Within the Mesozoic section, the Inyan Kara Group, which includes the Lakota and Fall River Formations, is used extensively as an aquifer, with various other units locally used to lesser degrees. Up to 4,300 ft of Cretaceous shales act as the upper confining layer to the Mesozoic aquifer units (Kyllonen and Peter, 1987).
Artesian conditions generally exist within the aforementioned aquifers, where an upper confining layer is present. This means that water in a well will rise above the top of the aquifer in which it is completed. If the water level, or potentiometric surface, is above the land surface, a flowing well will result. Similarly, artesian springs that originate from confined aquifers are common around the periphery of the Black Hills. The hydrogeologic setting of the Black Hills area is schematically illustrated in figure 6.
Figure 6. Schematic of hydrogeologic setting
Streamflow within the study area is affected by both topography and geology. The base flow of most Black Hills streams originates in the higher elevations, where increased precipitation and lower temperatures result in excess water being available for springflow and streamflow. Numerous streams have significant headwater springs originating from the Paleozoic formations on the western side of the study area (figs. 1 and 3). Most Black Hills streams generally lose all or part of their flow as they cross exposures of the Madison Limestone and Minnelusa Formation (Rahn and Gries, 1973). The Madison Limestone is a cavernous limestone and dolomite that is 300 to 650 ft thick (Rahn and Gries, 1973). Karst features of the Madison Limestone, including sinkholes, collapse features, solution cavities, and caves are responsible for the Madison's capacity to accept streamflow recharge. Recharge from streamflow loss also can occur to the Minnelusa Formation. The Minnelusa Formation consists of three units: an upper sandstone, up to 200 ft thick; a middle dolomite, sandstone, and shale with anhydrite in the subsurface, 200 to 300 ft thick; and lower sandstones and dolomites with basal shale, 0 to 300 ft thick (Rahn and Gries, 1973). Large springs occur in many locations downgradient from the streamflow-loss zones, most commonly within or near the outcrop of the Spearfish Formation, providing an important source of base flow to many streams beyond the periphery of the Black Hills (Rahn and Gries, 1973).
Summary of Precipitation Data for the Black Hills Area of South Dakota, Water Years 1931-98
As part of the Black Hills Hydrology Study, precipitation data were summarized for the Black Hills area in South Dakota for water years 1931-98 in a recently published U.S. Geological Survey Open-File Report OFR 00-329 (find under "Multimedia" tab). Precipitation data are available for numerous gaging locations; however, few gages have continuous, long-term records, and periods of missing record are common. Thus, a geographic information system (GIS) utilizing an inverse-distance weighting method was developed to generate spatial precipitation distributions from point precipitation data for the Black Hills area, based on available monthly records. The spatial distributions were used to estimate periods of missing record for selected gaging locations. The resulting monthly records of measured and estimated precipitation were tabulated for water years 1931-98 for 94 gaging locations. Average values for water years 1961-90, which is the period used for calculation of climatic normals, also were included with the tabulated data. The 94 gaging locations include both National Oceanic and Atmospheric Administration (NOAA) gages and U.S. Geological Survey (USGS) gages.
Digital Map Products
The Black Hills Hydrology Study was initiated in 1990 as a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents local and county cooperators. The purpose of the study is to assess the quantity, quality, and distribution of surface water and ground water in the Black Hills area of South Dakota and to define and to develop regional hydrogeologic conceptual models of the Black Hills (Driscoll, 1992; Strobel and others, 1998). The study area includes parts of Butte, Custer, Fall River, Lawrence, Meade, and Pennington Counties in western South Dakota.
As a result of this work and related activities with the Bureau of Reclamation, a number of digital data sets have been produced, including:
Below are multimedia items associated with this project.
Below are publications associated with this project.