Erosion Hot Spots and Targeting in the Chiques Watershed, Lancaster County, PA.
For LandStudies Inc.
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In the summer of 2019 WSI provided five datasets to LancStudies Inc. which included the following:
-Milldam Locations - Historic (18th - 19th centuries) mill dam locations, including information on whether or not the dams are breached and the timing of dam breach dates.
-Terrace polygons - Legacy Sediment terraces mapped along stream corridors in the Chiques Creek Watershed using the TerEx tool and manual editing. Terrace polygons indicate both lateral extent and thickness of Legacy Sediment terraces.
-DEM Differencing polygons - LiDAR DEM Difference data showing negative (erosion) change detection at 90% confidence interval.
-Heatmap - Heatmap raster showing densities of erosion volume from edited DEM difference polygons.
WSI recorded the results of this study in a report titled Stream Bank Erosion Analysis from LiDAR DEM Differencing for Landstudies, Inc., Chiques Creek Alternative Restoration Plan Assessment.
(Above) Map of legacy sediment fill terraces and historic mill dam locations in the Chiques Creek Watershed. 2014 USGS post-Sandy LiDAR.
(Above) Heatmap showing stream bank erosion in the Chiques Creek Watershed. A heatmap is a visual representation of data in which individual values for each cell in a DEM grid are represented as colors. 2014 USGS post-Sandy LiDAR.
A closeup view of legacy sediment terrace polygons (black) with multiple breached dam sites shown as well. 2014 USGS post-Sandy LiDAR.
In 2018, WSI completed an analysis of potential BMP installation sites in the Paxton Creek Watershed for the Center for Watershed Protection (CWP). WSI undertook field inspection of eleven sites provided by CWP and narrowed down on three which best satisfied the ideal conditions for creating a DEM from drone photogrammetry, among other considerations.
First, WSI created DEMs using 2016 LiDAR point cloud data. Then, after flying drones at the sites and creating high-resolution DEMs with 3-D modeling software, WSI used DEM differencing to determine negative change (erosion) over the nearly three year period.
WSI provided data sets displaying areas of high, medium, and low erosion rates complete with functionality allowing the user to click on stream segments to view calculated erosion rates with the value of error for each measurement. WSI also incorporated canopy and parcel data to further enhance the usefulness of the maps.
The project provided an accurate baseline of the pre-restoration conditions for developing proposed TMDL reductions at each site.