karst topography – developing a sinkhole inventory to protect groundwater quality
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Karst Topography – Developing a Sinkhole Inventory to Protect Groundwater Quality. Presenters: Stacey Jarboe and John-Paul Brashear Stantec Consulting Services Inc. 2009 Indiana GIS Conference. What is karst topography?. Created when groundwater dissolves sedimentary rock such as limestone - PowerPoint PPT PresentationTRANSCRIPT
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Karst Topography – Developing a Sinkhole Inventory to Protect
Groundwater Quality
Presenters: Stacey Jarboe and John-Paul Brashear
Stantec Consulting Services Inc.
2009 Indiana GIS Conference
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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
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A Karst Landscape
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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.
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Rare Sinkholes
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More Common Sinkholes
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Importance to watershed management?
• Pollutants can be rapidly transported to groundwater systems without the benefit of soil filtration.
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Indian CreekWatershed
Drains 256 square miles
Harrison, Floyd, Clark Counties
Over 66 miles of “impaired” streams
Numerous karst features, including Binkley Cave
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Indian Creek WatershedGrant Funded
• Clean Water Act Section 205(j) Grant : – Watershed Coordinator &
Committee– Public Outreach – Water Quality Monitoring– Inventory Sinkholes – Watershed Management Plan
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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.
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Harrison County provided 2 foot and 4 foot interval contours that were derived from LIDAR data.
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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.
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Possible sinkhole locations were represented by closed contour depressions within the topographic vector data;
which were identified by using ArcGIS software.
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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.
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Overall result of potential sinkhole locations within the Harrison County portion of the Indian Creek
Watershed.
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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 UseUrban Land Use Urban Area Sinkholes
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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.
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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
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Geoprocessing steps within ArcMap• Create closed contour depression polygons from the contour data• Select by attributes
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Export data out as a new shapefile
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Convert to polygon: ArcToolbox – Data Management Tools – Features – Feature To Polygon
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Create closed contour depression polygon centroids: ArcToolbox – Data Management Tools – Features –
Feature To Point
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Filter out developed land use classes from USGS landcover shapefile
Select by attributes
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Export data out as a new shapefile
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Intersect centroids with developed land use to create developed area centroids
• Select by location: select features from centroids that intersect with developed land use
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Export selected features out as a new shapefile containing centroids within developed areas
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Questions or comments?Contact Information:
John-Paul BrashearSenior GIS AnalystStantec Consulting Services Inc.350 Missouri Ave ste 100Jeffersonville, IN [email protected]
Stacey JarboeGIS AnalystStantec Consulting Services Inc.350 Missouri Ave ste 100Jeffersonville, IN [email protected]