Statemap Program in Iowa
Passage of the National Geologic Mapping Act of 1992 provided a stimulus for detailed geologic mapping of the U.S. directed towards the resolution of environmental problems. This decade-long mapping program is administered by the U.S. Geological Survey and includes a “STATEMAP” component which offers partial financial support for geologic mapping to state geological surveys through a competitive grant process. During the first year of the program in 1993-94, the Geological Survey Bureau mapped a segment of the Mississippi River valley covered by the Blanchard Island and Letts 7.5 minute quadrangles in southern Muscatine and northern Louisa counties. Tools unavailable in the earlier years of traditional geologic mapping were applied. These include satellite images to assist with mapping boundaries between different geologic deposits, and computer technology to convert maps to digital databases, which then can be transferred in electronic form, printed as colored maps, combined with other geographic information, and be easily updated.
The completed Letts and Blanchard Island quadrangles encompass about 110 square miles (282 sq. km) of the Mississippi valley and adjoining uplands south of Muscatine in eastern Iowa and adjacent western Illinois. The goal of the project was to map geologic materials to a depth of five meters (about 18 ft) at 1:24,000 scale (1 in = 2,000 ft) in order to provide baseline geologic information for a host of environmental and resource issues. The mapped area includes Muscatine Island, a portion of the Mississippi valley under competitive pressures from agriculture and industry for land and groundwater. A portion of the upper Mississippi River navigation system and several wildlife refuges and game management areas also occur in this area, and present a series of contrasting resource management issues. Land degradation from soil erosion and headward advance of Mississippi tributary valleys, as well as landfill siting are important issues on the upland.
Several sources of subsurface information, including water well records, engineering boring records obtained from public utilities and the Iowa Dept. of Transportation, monitoring well records of the U.S. Geological Survey, borings made by the Geological Survey Bureau, and published soil surveys were used to construct the geologic maps. These data were compared to landscape patterns on high-altitude air photos and satellite imagery to formulate and draw the map units. Thirty-two map units, each depicting a unique succession of geologic materials to a depth of five meters, were developed.
The published maps, related cross-sections, and explanatory text [Geological Survey Bureau, Open File Map Series 94-1 (Surficial Geologic Materials of the Letts, Iowa Quadrangle) and 94-2 (Surficial Geologic Materials of the Blanchard Island, Illinois-Iowa Quadrangle)], provide a detailed view of the geologic materials that most affect day-to-day activities in this area, and give users a sound base of geologic information from which to make resource decisions.
In July 1994, the Geological Survey began work on its second Statemap project, with the inauguration of a three-year program to map the shallow geology of Linn County. In compliance with national program directives, the Geological Survey Bureau assembled a statewide geologic mapping advisory panel that consisted of individuals from government, academia, professional societies, engineering firms, and mineral producing firms. This panel, representing potential users of geologic information, selected Linn County as the area where surficial geologic mapping could be most usefully applied to recognized environmental problems. In addition to the federal award, financial support for the mapping has been provided by the Linn County Engineering, Planning and Zoning, Regional Planning, and Solid Waste agencies, as well as the cities of Cedar Rapids, Hiawatha, and Marion, all of whom are anticipated end-users of the map information.
During the 1994-95 project year, the Cedar Rapids North and Marion 7.5 minute quadrangles are being mapped, and the county-wide bedrock geologic and bedrock surface topographic maps are being updated. In the 1995-96 project year, the Cedar Rapids South and Central City 7.5 minute quadrangles will be mapped and updates to the county-wide bedrock geology and topography will continue.
All maps are being compiled using geographic information system (GIS) technology and will be stored in DNR's Geographic Information System Library. Use of GIS technology will facilitate digital access for a large number of users with varied interests and provide flexible use of the geologic mapping for various applied purposes in the future.
It is anticipated that the information developed by the Statemap project will be used to address a variety of problems related to development and the impact of increasing population density on geological resources. Possible applications include evaluating surface and subsurface drainage problems, groundwater contamination, vulnerability of groundwater to contamination, suburban expansion into areas of sinkholes (karst), and long-range plans for the county sanitary landfill.