Lidar-Based Roadside Ditch Mapping Report
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Chesapeake Bay Program Partnership’s (CBP) Roadside Ditch Management Team (RDMT) aims to address the urgent need for an inventory of roadside ditches. An estimated extent of the existing ditch network will enable CBP and environmental planners to establish restoration priorities, recommend Best Management Practices, and model potential sediment and nutrient reductions across the Chesapeake Bay watershed. Through a pilot study in two Pennsylvania counties, the Chesapeake Conservancy’s Conservation Innovation Center (CIC) has produced a dataset cataloging roadside ditch locations while addressing two mapping priorities: 1) errors of commission should be minimized and 2) ditches included in the dataset should be contiguous and not fragmented. CIC has tested a range of geospatial workflows aimed at limiting commission while emphasizing data contiguity and found that applying thresholds to a combination of flow accumulation, positive topographic openness, and topographic convergence index appears to perform best. Performance of the results in achieving RDMT’s goals has been assessed using the visual interpretation of aerial imagery by analytical staff. Recommended next steps include validating results with field-verified data, establishing a semi-automated approach for setting GIS data thresholds, developing an accuracy assessment methodology, and prioritizing ditches for restoration based on criteria set forth by the RDMT.