Data for statewide assessment of New York's karst aquifers with an inventory of closed-depression and focused-recharge features

The New York State Departments of Environmental Conservation and Health are concerned about groundwater contamination in the carbonate-bedrock aquifers with the potential to host karst features throughout New York State, especially relating to the unintended introduction of chemical or agricultural contamination into these aquifers. USGS Scientific Investigations Report, SIR 2020-5030 (Kappel and others, 2020), provides local and State regulators and the public the information needed to determine the extent of carbonate bedrock in New York, the associated environmental impacts of karst, and the means to protect New York?s karst water resources. The four geodatabases presented in this data release were compiled in support of SIR 2020-5030. Closed depression-focused recharge is one potential pathway for aquifer contamination. A closed depression is any enclosed area that has no surface drainage outlet and from which water escapes only by evaporation or subsurface drainage. On a topographic map a closed depression is typically represented by a hachured contour line forming a closed loop. The map representation applies to closed depressions of both natural and anthropogenic origin. Closed depressions formed by natural processes need not be karst in origin to represent a source of focused-recharge. Three of the four geodatabases in this data release form a comprehensive inventory of all closed depressions, natural and anthropogenic, within the State which are proximal to carbonate, evaporite, or marble units and that have the potential for developing karst features. The fourth geodatabase in this data release contains a digital representation of the study area boundary adopted for the GIS analyses. The three closed depression inventory geodatabases were compiled in the following order: 1) Digital Contour Database of Closed Depressions, 2) Digital Raster Graphic Database of Closed Depressions, and 3) LiDAR Database of Closed Depressions. There is no duplication of features among these three geodatabases. Additionally, the closed depressions inventoried for this data release, were compared with closed depressions mapped in other published geospatial data to eliminate duplication with those datasets. The datasets referenced were the New York State Department of Environmental Conservation Mining Database and the National Hydrography Dataset waterbody features. The Digital Contour Database of Closed Depressions contains features derived from data associated with U.S. Geological Survey Scientific Investigations Report 2012-5167. The source data is a statewide contour dataset that was generated from the National Elevation Dataset (NED) and the National Hydrography Dataset (NHD) in a fully automated process. Closed depressions included in the Digital Raster Graphic Database of Closed Depressions were digitized from an assemblage of approximately 650 Digital Raster Graphic (DRG) images of scanned U.S. Geological Survey 1:24,000-scale topographic maps. A DRG is a scanned image of a U.S. Geological Survey topographic map that can be added as a background layer in a GIS. The LiDAR Database of Closed Depressions contains features generated from high-resolution LiDAR-derived bare-earth DEMs obtained from the New York State Office of Information Technology Services. At the time of analysis (2017) LiDAR data existed for approximately 65 percent of the study area. The DEMs were processed to identify depressions with an area of at least 4,047 square meters (1-acre) and a depth of at least 1-meter. These threshold values are greater than what is typically used for lidar-based sinkhole identification studies. For the purpose of this study, the use of lidar was primarily intended to identify closed depressions that were not represented in the Digital Raster Graphic Database, in the same manner that the DRG images were used to identify closed depressions not represented in the Digital Contour Database. For that reason, the threshold values were based on random sampling of DRG-derived closed depressions within the study area and represent the approximate mean geometric characteristics of the closed depressions sampled. For ongoing and planned larger-scale county-based assessments in New York, the thresholds will be reduced to 10- and 30-centimeters depth and 100 square meters.