Karst Topography – Developing a Sinkhole Inventory to Protect Groundwater Quality Presenters: Stacey Jarboe and John-Paul Brashear Stantec Consulting Services Inc Indiana GIS Conference

What is karst topography? Created when groundwater dissolves sedimentary rock such as limestone Forms caves and sinkholes Beautiful but fragile, and vulnerable to erosion and pollution

A Karst Landscape

What is a sinkhole? Rounded depressions in the landscape that are often caused by collapsed caves Sinkholes vary in size and depth Collect surface water running off the surrounding land which goes directly into the groundwater.

Rare Sinkholes

More Common Sinkholes

Importance to watershed management? Pollutants can be rapidly transported to groundwater systems without the benefit of soil filtration.

Indian Creek Watershed  Drains 256 square miles  Harrison, Floyd, Clark Counties  Over 66 miles of “impaired” streams  Numerous karst features, including Binkley Cave

Indian Creek Watershed Soils and Septic

Indian Creek Watershed Grant Funded Clean Water Act Section 205(j) Grant : –Watershed Coordinator & Committee –Public Outreach –Water Quality Monitoring –Inventory Sinkholes –Watershed Management Plan

Using geoprocessing tools in an ArcGIS environment, digital elevation data was used to develop a sinkhole inventory that consisted of 14,000 possible sinkholes within the Harrison County portion of the Indian Creek watershed.

Harrison County provided 2 foot and 4 foot interval contours that were derived from LIDAR data.

What is LIDAR Data? Light Detection and Ranging (LIDAR) is a remote sensing system used to collect topographic data. This data is collected with aircraft-mounted lasers that record elevation measurements with a vertical precision of 15 centimeters (6 inches). A high precision GPS antenna is also mounted on the aircraft; and the end product is an accurate and geographically registered XYZ position for every data point collected. These data points allow the generation of a digital elevation model (DEM) of the ground surface.

Possible sinkhole locations were represented by closed contour depressions within the topographic vector data; which were identified by using ArcGIS software.

The centroid (center of gravity/geometric center) of the closed contour depressions were identified by using ArcGIS software and used to create point features for possible sinkhole locations.

Overall result of potential sinkhole locations within the Harrison County portion of the Indian Creek Watershed.

Within watershed planning; sinkholes that are located in urban areas are of greater interest based on stormwater volume and quality. As a result of this USGS land use categories were implemented to classify the GIS-derived sinkhole locations into two groups: developed and undeveloped. Overall Land Use Urban Land UseUrban Area Sinkholes

Overall limitations of the dataset Over-estimation and under-estimation of the number of actual sinkholes; as well as inaccurate locations are an issue. Other natural and man-made depressions such as drainage features, ponds, and quarries can be represented by closed depression contours. Sinkholes may be overlooked that are located in forested areas, steep terrain, or newly formed.

Because of these inherent limitations; random sampling was used to select the GIS-derived sinkhole locations for aerial review. A review of high resolution aerial photography was performed on a subset of the GIS-derived sinkhole locations to characterize the features as either a probable sinkhole; or as a probable non-sinkhole. Actual field verification/ground truthing was also used on a small number of potential sinkhole locations by implementing mobile GIS tools to help increase overall dataset accuracy. Wal-Mart Parking Lot

Geoprocessing steps within ArcMap Create closed contour depression polygons from the contour data Select by attributes

Export data out as a new shapefile

Convert to polygon: ArcToolbox – Data Management Tools – Features – Feature To Polygon

Create closed contour depression polygon centroids: ArcToolbox – Data Management Tools – Features – Feature To Point

Filter out developed land use classes from USGS landcover shapefile Select by attributes

Export data out as a new shapefile

Intersect centroids with developed land use to create developed area centroids Select by location: select features from centroids that intersect with developed land use

Export selected features out as a new shapefile containing centroids within developed areas

Questions or comments? Contact Information: John-Paul Brashear Senior GIS Analyst Stantec Consulting Services Inc. 350 Missouri Ave ste 100 Jeffersonville, IN Stacey Jarboe GIS Analyst Stantec Consulting Services Inc. 350 Missouri Ave ste 100 Jeffersonville, IN