Kansas Geological Survey, Open-file Report 2008-9

Methodology and Data Used to Construct the Surficial Geology (M-119A) and Water-bearing Units (M-119B) Maps of the Tallgrass Prairie National Preserve, Chase County, Kansas

by Robert S. Sawin
KGS Open-file Report 2008-9

Introduction

A better understanding of the geology and water resources of the Tallgrass Prairie National Preserve is critical to long-term management of the preserve's natural resources. The first phase (springs inventory) of a two-part study designed to characterize the geology and water resources on the preserve was completed by the Kansas Geological Survey in 2001 (Sawin and Buchanan, 2001). The second phase--construction of a detailed geologic map and characterization of the hydrogeologic setting--required the gathering of surficial geologic data and mapping from aerial imagery. The geologic map (Sawin, 2008), combined with the springs data, has been used to delineate the preserve's water-bearing rock units (Sawin and Buchanan, 2008).

The geologic map, hydrogeologic map, and supporting data provide the National Park Service and The Nature Conservancy with basic, benchmark information about the nature of the preserve's geology and water resources. Because the preserve's land-use patterns (such as burning regimes, grazing, and human visitation) are changing, and will continue to change in the future, it is important to have these baseline data on the geology and hydrogeologic setting. In addition, geologic and water-resource knowledge gained at the preserve will be useful to resource managers, researchers, and others at the preserve and throughout the Flint Hills region.

Methods

Field work for the geologic map involved systematically locating outcrops by walking each drainage or investigating known outcrops or exposures that were evident on aerial imagery. In most cases, only outcrops where the contact between mappable units could be recognized were recorded. These localities are referred to as control points (hence the CP designation before each number) because they function as "ground truth" for the mapping that was done on the aerial imagery. Each control point was recorded electronically on a WalkAbout Hammerhead XRT Tablet PC with built-in GPS (global positioning system). The tablet PC utilizes ArcGIS 9 ArcMap software by Environmental Systems Research Institute (ESRI) and contains the following data sets:

• National Elevation Dataset (NED)--1:24,000-scale U.S. Geological Survey topographic map (Strong City, Kansas, quadrangle)
• 2006 Farm Service Agency (FSA) National Agriculture Imagery Program (NAIP) color aerial imagery (1m resolution)
• 2003 Farm Service Agency (FSA) National Agriculture Imagery Program (NAIP) color aerial imagery (2m resolution)
• 2002 Digital Orthophoto Quarter Quadrangles (black and white)
• Natural Resources Conservation Service (NRCS) Soil Survey (SSURGO)

Other attributes (e.g., geologic contact) were also recorded electronically (see Table 1). In addition, the outcrop and other related details were digitally photographed, and if warranted, the section was measured and described.

The electronic data collected in the field were transferred to a desktop PC that was loaded with the same software and layers as on the tablet PC. Using ArcMap, the geologic contacts were digitally drawn on the 2006 NAIP color imagery (other layers were utilized where appropriate) at scales ranging from 1:2,000 to 1:5,000 (most units were mapped at 1:3,000 or 1:3,500), depending on what scale best characterized the contact. Along with the aerial imagery and topographic map, field data, photographs, and measured sections were incorporated into the geologic interpretation.

Surficial Geology Map

The surficial geology map (Sawin, 2008) graphically shows the distribution, rock type, and age of bedrock near the earth's surface. It can be used to identify surface and subsurface lithologic units and their stratigraphic relationships, show geologic structures, delineate thick surficial materials such as alluvium, and show the spatial orientation of these features. As planning, development, and renovation continue at the Tallgrass Prairie National Preserve, basic geologic information about the near-surface bedrock geology at specific sites will be important. The geologic map will be useful in construction and engineering projects, in understanding ground-water characteristics, and for environmental assessments. Understanding the near-surface geology and incorporating geologic evaluations into the planning process can help prevent future construction, resource, and environmental problems.

Included with the map is a stratigraphic rock column that depicts the vertical sequence, thickness, and lithologies of the geologic units. A short, generalized description of each geologic unit is also included. East-west and north-south cross sections show the vertical relationship of the rock units.

Hydrogeologic Map

The preserve is underlain by alternating layers of limestone and mudstone. Precipitation infiltrates the subsurface and gravity moves the water downward. Fractures in the limestones, which have been widened by flowing water, are conduits for the subsurface movement of water. The mudstones are less permeable and separate the water-bearing limestones; however, the mudstones are fractured enough to allow very slow downward movement of water from one limestone to the next. Where the water-bearing limestones intersect the land surface, the water in the limestones can discharge onto the land surface as springs or seeps. These springs are classified as contact springs, the most common type of spring at the preserve and in the Flint Hills (Buchanan, Sawin, and Lebsack, 1998; Sawin, Buchanan, and Lebsack, 1999).

Delineation of water-bearing limestones associated with springs at the preserve can be generally determined by combining information from topographic and geologic maps. By superimposing the rock unit onto a topographic map, the areal boundaries (defined by the intersection of the rock outcrop with the land surface) of the water-bearing units (Sawin and Buchanan, 2008) have been determined. The distribution and occurrence of springs at the preserve were used to identify the water-bearing limestones (Sawin and Buchanan, 2001; Table 2).

Interactive Map

The geologic and hydrogeologic information that was generated in this study has been displayed as an interactive map of the geologic and water-bearing units within the preserve. The interactive map will be served over the Internet using ESRI's ArcIMS software.

A user-friendly interface has been developed to allow the user to click on a geologic unit and retrieve the name, lithology, description, and hydrogeologic characteristics of that unit. By clicking on a geologic control point or spring location, information about the outcrop (photos, measured sections, etc.) or spring (flow, chemical analysis, etc.) will be displayed.

The interactive map is a server-side application and thus will not require the user to have a high-speed Internet connection, a robust computer, or to acquire special software to make use of the application. Both the tabular and geospatial databases will be made available for download from the interactive-map web site.

The interactive-map web site is available at http://geoportal.kgs.ku.edu/tallgrass (Edit, 03/21/2024: The interactive map is no longer available).

Digital Maps and Data

Digital versions of the hard-copy cartographic maps have been produced using ESRI's ArcGIS software. A CD has been created for the National Park Service that contains the geologic maps and supporting geospatial databases. ArcReader, which can be thought of as the Adobe Acrobat Reader for maps, allows the user to navigate through the map (pan, zoom-in, zoom-out), identify map features, toggle on/off the display of geospatial data layers, and print selected maps.

References

Buchanan, R., Sawin, R., and Lebsack, W., 1998, Kansas springs: Kansas Geological Survey, Public Information Circular 11, 4 p.

Sawin, R. S., 2008, Surficial geology of the Tallgrass Prairie National Preserve, Chase County, Kansas: Kansas Geological Survey, Map M-119A, scale 1:12,000.

Sawin, R. S., and Buchanan, R. C., 2008, Water-bearing units of the Tallgrass Prairie National Preserve, Chase County, Kansas: Kansas Geological Survey, Map M-119B, scale 1:12,000.

Sawin, R., and Buchanan, R., 2001, Springs inventory--Tallgrass Prairie National Preserve, Chase County, Kansas: Kansas Geological Survey, Open-file Report 2001-40 (Revised July 2008), 17 p.

Sawin, R., and Buchanan, R., 2000, Water quality of selected springs--Tallgrass Prairie National Preserve, Chase County, Kansas: Kansas Geological Survey, Open-file Report 2000-01 (Revised July 2008), 31 p. [available online]

Sawin, R.S., Buchanan, R.C., and Lebsack, W., 1999, Flint Hills springs: Transactions of the Kansas Academy of Science, v. 102, no. 1-2, p. 1-31.

Table 1. Geologic Control Points. B/ = base, T/ = top.

Table 2. Spring Data (from Sawin and Buchanan, 2001). Spring numbers in ( ) are from Sawin and Buchanan, 2000. Data was collected in April 2001.

Kansas Geological Survey, Geology
Placed online Oct. 3, 2008
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