Targeting Best Management Practices (BMPs) to Critical Portions of the Landscape: Using Selected Terrain Analysis Attributes to Identify High-Contributing Areas Relative to Nonpoint Source Pollution

Digital terrain analysis is a geographic information system (GIS) tool that allows users to geospatially describe landscapes in a hydrological, biological, or geomorphological context. It has been used extensively in the past few decades for several different types of applications (Wilson and Gallant, 2000). Although the basis of the terrain analysis process has been essentially unchanged since its first applications, the quality of digital terrain data has advanced greatly since that time. The following report details an investigation of the effectiveness of terrain analysis to identify areas that may be critical for restoring and protecting water quality. This investigation begins with analysis using coarse-scale (30-meter) elevation data that is available for the entire United States and concludes with analysis using fine-scale (3-meter) data that is becoming increasingly available for many areas. The effectiveness and feasibility of terrain analysis on these different scales is included. Critical areas are defined as portions of the landscape that accumulate overland flow and are hydrologically connected to surface waters, either by an overland flow path or by sub-surface drainage. These areas have a higher likelihood of conveying contaminants to surface waters than other portions of the landscape. Using 30-m data, three different critical areas are identified: artificially drained upland depressions, riparian areas, and ravines. 3-m LiDAR data identified finer-scale features such as field gullies or side inlets.