Inventory and Sediment Modeling of Unpaved Roads for Stream Conservation Planning

The streams and rivers of the Ozark Plateaus are an unrivaled natural resource for the region. They provide habitat to some of the North America’s most abundant and rich biodiversity, while also serving as water sources for human drinking, agricultural, and recreational needs. The Nature Conservancy (TNC) has identified several priority watersheds through its Ozarks Ecoregional Conservation Assessment of 2003, where it focuses its on-the ground conservation planning and implementation efforts.Sedimentation from unpaved roads is a primary threat to water quality in Ozark streams. TNC has partnered with various organizations including the US Forest Service (USFS), the Watershed Conservation Resource Center (WCRC), and others to develop a multi-phased approach to address the impacts of unpaved roads on these priority watersheds.The first step in the approach utilizes advanced GIS/GPS technologies to develop a detailed vehicle-based road inventory of the target watershed or subwatershed. Sub-meter differential GPS with customized data dictionaries are used to characterize the location and function of sediment-producing and conveying features of the road infrastructure, including the road surface, prism and slope, ditches, bars, lead-offs, culverts, crossings, and outlets. The road inventory yields a comprehensive geodatabase and map series of the mapped features.A stratified random sample of the inventoried road network is then measured to generate sediment yield predictions on ten percent of the road network. Detailed field measurements are collected with differential GPS and customized data dictionaries. The data are entered into the Water Erosion Prediction Project (WEPP) model, a process-based erosion prediction model developed by multiple federal agencies over the past 20 years. With sediment yields predicted for sample sites, erosion predictions are then extrapolated for the entire study watershed using the road inventory geodatabase.Once sedimentation yields are predicted for each road segment in the entire study area, priority sub-watersheds are identified in the GIS using watershed sediment accumulation tools. These sub-watersheds with high potential for sediment yield may be compared to species inventory data, stream bank erosion surveys, and other land use information to set priorities for conservation planning and prioritization efforts. Priority infrastructure maintenance improvements are also identified through features that were flagged in the road inventory geodatabase as needing repair or replacement.Road maintenance workshops are held with USFS engineers, county road crews, and other partners to transfer the inventory information, present the findings of the study and to demonstrate best management practices for road maintenance.Since 2004, TNC and its partners in the Arkansas have worked in three priority Ozark watersheds to inventory over 600 miles of unpaved roads and 3000 associated point features in an area greater than 900 square miles. The area comprises over thirty 6th level (12-digit) HUCs