![]() ![]() ![]() ![]() Changes in topography at 8 of the 11 points ranged from 0.09 to 0.63 ft and topography remained constant, or within the measurement uncertainty, for 3 of the 11 points.Two cross sections were constructed through the depression area The relative horizontal and vertical (altitude) accuracies of the 11 topographic measurements collected in March 2012 were Â☐.098 and Â☐.060 feet (ft), respectively. These points were measured during the July 2008 survey and measured again during the March 2012 survey to evaluate the relative accuracy of the altitude measurements. Two additional control points were established at stable locations along Hillview Avenue, which runs parallel to the embankment. Survey measurements of the depression area indicated that the land-surface altitude at 8 of the 11 points decreased beyond the accepted measurement uncertainty during the 44 months from July 2008 to March 2012. The points were surveyed again in March 2012 to evaluate temporal changes in land-surface altitude. Eleven points were surveyed along the edge of the depression area and at arbitrary locations within the depression area by using robotic land-surveying techniques. A point of origin was established for the topographic survey by using differentially corrected positional data collected by a global navigation satellite system. Geological Survey surveyed the topography of land surface in this depression area by collecting high-accuracy (resolution less than 1 inch) measurements. ![]() Monthly site inspections at the reservoir indicated an approximately 90-square-foot depression in the land surface directly upslope from a seep that has episodically flowed since 2007. Geological Survey began a cooperative study with New York City Department of Environmental Protection to characterize the local groundwater-flow system and identify potential sources of seeps on the southern embankment at the Hillview Reservoir in southern Westchester County, New York. Services Contact Site Map Go Global Land Survey(GLS) Data Access ESDI Download via Search and Preview Tool gls The Global Land Survey (GLS) collection of Landsat imagery is designed to meet a need from Availability: GLS 1975, 1990, 2000, and 2005 are available to the public for free at the US Geological Surveyĭetecting temporal change in land-surface altitude using robotic land-surveying techniques and geographic information system applications at an earthen dam site in Southern Westchester County, New York ![]()
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