USGS OFR 01-223: <acronym>GIS</acronym> Applications to Karst Studies: Frederick Valley, Maryland

Digital Mapping Techniques '01 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 01-223

Geographic Information Systems (GIS) Applications to Karst Studies: Frederick Valley, Maryland

By David K. Brezinski and Liana E. Dunne

Maryland Geological Survey
2300 St. Paul Street
Baltimore, MD 21218
Telephone: (410) 554-5500
Fax: (410) 554-5502
e-mail: dbrezinski@MGS.md.gov, ldunne@MGS.md.gov

INTRODUCTION

The Frederick Valley, a lowland underlain by limestone rocks in eastern Frederick County, Maryland, is one of the most rapidly developing areas in the State. The Maryland Geological Survey (MGS) in cooperation with the Maryland State Highway Administration (SHA) is currently studying the geology of the Frederick Valley in an effort to evaluate the frequency and character of karst features and to assess their relationship to geologic formations (lithology), man-made features (roads, quarries), or other attributes that may be responsible for their distribution. A major goal of this study is to produce detailed geologic and karst features maps that are fully GIS functional and can be integrated into many GIS systems. Highway designers and engineers can benefit from having such detailed analysis of karst hazards to help them develop cost effective and safe highway systems for the State of Maryland.

INTEGRATING GEOLOGY AND GIS

Although the original agreement between the MGS and the SHA did not involve the production of digital maps, early in the project it was recognized that the use of a GIS to compile the maps would facilitate on-going spatial data analysis by MGS geoloGISts. The six 7.5-minute quadrangles included in the study are Buckeystown, Point of Rocks, Woodsboro, Catoctin Furnace, Frederick, and Walkersville. The Maryland Geological Survey's goal is to produce a total of thirteen digital maps to satisfy this agreement.

The initial digital geologic map to be produced was the Buckeystown 7.5-minute quadrangle. The base layers, including topology, hydrology, transportation, and political boundaries, were developed from digital line graph (DLG) data from the United States Geological Survey (USGS), and converted into coverages in ArcInfo 8.0.1. The digital geologic layers and the supporting database were developed from information provided by the principal investigator. Data for some layers, including bedrock geology, Quaternary alluvium, and bedding and planar features, were collected using standard field techniques and compiled on a series of mylar sheets. Mylars were scanned to raster images which were then transformed to vector files using a combination of heads-up digitizing and raster to vector conversion. The karst features layer data were collected in the field using a global positioning system (GPS). The karst features layer was developed as an ArcInfo point coverage file from the GPS spot locations of sinkholes, depressions and springs. Additional GPS data for streambeds and drainage areas were collected and used in a spatial analysis of local sinkhole development, discussed below. The perimeters of selected large sinkholes are measured periodically using a GPS to monitor growth rate.

Creation of the two digital maps, geology and karst, per quadrangle involves assembling appropriate GIS layers and associated data tables with map layout elements. This is all being completed in ArcInfo 8.0.1 software. The final release of all digital elements will be available as coverages, shapefiles, and .PDF formats. With the advent of the new ArcGIS, duplicate layout production in both ArcView and ArcInfo will not be necessary.

EVALUATING GEOLOGIC PROBLEMS WITH GIS

Potential patterns of karst development can be identified by analyzing the digital karst data using a GIS. One of the issues under investigation is the role of stratigraphy in the development of karst features. An inventory was made of the number and type of karst features present in the limestone formations. The Frederick Valley has several karst prone stratigraphic intervals. While the Frederick Valley proper is underlain by the Cambrian and Ordovician strata of the Frederick and Grove Formations, an ancillary area to the west is underlain by the limestone and dolomite conglomerates of the Triassic Leesburg Formation. Although some earlier, unpublished, studies suggest that the karst features are largely restricted to the Ordovician Grove Formation, recent geologic mapping, utilizing digital techniques, indicates both the Grove and the Frederick Formation are susceptible to karst sinkhole activity. Based on the number and types of karst features present in each formation, both formations seem to be equally karst prone.

An important issue in karst development concerns the restructuring of drainage from highway development and quarry operations. In a particular region along Interstate 70 in Frederick City, the proximity of this sinkhole-prone area to both the nearly century old Frederick Quarry and Interstate 70 has raised questions as to which factor is responsible for the karst proclivity. Precise GPS location of the recently active and historically active karst features initially fails to yield any definitive answers for this active karst area. However, when GPS transects, made along the historic drainages, are added, a closer correlation is apparent. When the drainage lowland is added to the stream channel transects, many, if not most, of the sinkholes fall within these lowland areas. Consequently, this close correlation of the stream channels with the karst features points to the theory that karst features are predominately drainage related. This relationship is important when considering future highway development or city expansion.

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