Abstract
The Valley region of Virginia, USA, features cave and karst systems. Variation in surface topography and vegetation within these systems significantly affects sediment accumulation in cave ecosystems. Remote sensing and GIS tools effectively analyze surface conditions, including vegetation cover and its influence on sediment buildup in caves. This study involved collecting high-resolution drone imagery, such as LiDAR, multispectral, and thermal data near Owl Cave in Highland County, VA, to understand the sediment accumulation process inside the cave system. High-resolution digital elevation models (DEMs) were created from LiDAR point clouds, and vegetation indices like Normalized Difference Vegetation Index (NDVI) were calculated using multispectral data. Additionally, the sediment transport index (STI) and topographic position index (TPI) were computed from elevation models to evaluate how surface vegetation impacts erosion and sediment transport. Sediments were characterized physically and chemically by collecting two cores: one from inside the cave and one from the entrance at different depths, analyzing particle size via laser diffraction and organic carbon content through loss on ignition methods. A pooled T-test compared variability in particle size and organic carbon among the cores. Results indicated that samples from inside the cave contained significantly more sand, while silt was higher at the entrance; clay content differences were not significant. Organic carbon inside the cave was below 5%, whereas at the entrance, it ranged from about 7% at the surface to below 5% at deeper depths. The weak correlation between NDVI and STI suggests that topography influences sediment deposition more than vegetation, a pattern common in karst terrains. Lower TPI values (mean = -2.19) reflect higher depositional zones around the cave. Variations in particle-size distribution inside and outside the cave are due to sediment influx during high-flow events and weathering of the cave walls.
DOI
https://doi.org/10.5038/9781967518012.1010
Figure 1: Map of the study location. The image on the top left: Water Sinks Depression (red dot) in Highland County, VA. Image on the right: RGB orthomosaic derived from drone data. The image on the lower left: DEM and DSM of the study region (maroon dot: Owl Cave). The blue line represents the Sinking Creek which flows around the Water Sinks Depression.
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Figure 2: (A). Digitized geology map of the study location, denoting project site (red star) (source Haynes and Whitmeyer, 2010). (B). Map of the Owl Cave showing the cave passages modified from maps of Lucas, 2015a).
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Figure 3: Workflow of LiDAR Data Collection (aerial and cave inside), processing and Digitizing of the Geologic Map of Williamsville Quadrangle.
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Figure 4: Variation in PSD (%) with soil depth (cm) in cave inside (IN) samples. Error bars show the standard deviations.
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Figure 5: Variation in PSD (%) with soil depth (cm) in cave entrance (ENT) samples. Error bars show the standard deviations.
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Figure 6: Variation in OC (%) with soil depth (cm) in cave entrance (ENT) and inside (IN) samples.
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Figure 7: Maps showing (A) NDVI, (B) STI, (C) TPI, and (D) SPI values for the study region. Black box shows the approximate location of Cave. 3D map of the Owl Cave is inside the black box for each map (not to a scale) The vertical Datum is North American Vertical Datum 88 (NAVD 88).
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Figure 8: (A). Previously drawn Owl Cave map (modified from maps of Lucas, 2015a). (B). Derived 3D model from the Owl Cave using the point cloud data from the GEOSLAM LiDAR Scanner. The star indicates the approximate location of the sediment pile.
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Table 1: Elevation (m), slope (%), and hydrological/topographical indices of the study region.
Investigating Sediment Accumulation Dynamics via Integration of GIS and Remote Sensing Tools Along with Physical/Chemical Characteristics of Sediments in Owl Cave, Highland County, Virginia
The Valley region of Virginia, USA, features cave and karst systems. Variation in surface topography and vegetation within these systems significantly affects sediment accumulation in cave ecosystems. Remote sensing and GIS tools effectively analyze surface conditions, including vegetation cover and its influence on sediment buildup in caves. This study involved collecting high-resolution drone imagery, such as LiDAR, multispectral, and thermal data near Owl Cave in Highland County, VA, to understand the sediment accumulation process inside the cave system. High-resolution digital elevation models (DEMs) were created from LiDAR point clouds, and vegetation indices like Normalized Difference Vegetation Index (NDVI) were calculated using multispectral data. Additionally, the sediment transport index (STI) and topographic position index (TPI) were computed from elevation models to evaluate how surface vegetation impacts erosion and sediment transport. Sediments were characterized physically and chemically by collecting two cores: one from inside the cave and one from the entrance at different depths, analyzing particle size via laser diffraction and organic carbon content through loss on ignition methods. A pooled T-test compared variability in particle size and organic carbon among the cores. Results indicated that samples from inside the cave contained significantly more sand, while silt was higher at the entrance; clay content differences were not significant. Organic carbon inside the cave was below 5%, whereas at the entrance, it ranged from about 7% at the surface to below 5% at deeper depths. The weak correlation between NDVI and STI suggests that topography influences sediment deposition more than vegetation, a pattern common in karst terrains. Lower TPI values (mean = -2.19) reflect higher depositional zones around the cave. Variations in particle-size distribution inside and outside the cave are due to sediment influx during high-flow events and weathering of the cave walls.