Road Drainage Diversion Potential

Step Wise Guide

Transportation/Energy

· What is the cumulative length and quality of fish habitat above every road crossing in my watershed?

Roads can alter natural hillslope drainage patterns, including concentrating flow and focusing it onto sensitive areas. Roads, cutslopes and inside ditches can intercept hillside drainage and redistribute it onto landslide prone hillsides. Concentrated road drainage can also lead to surface erosion and gullies. Roads, particularly unpaved ones, can be a major source of sediment to streams and rivers.

Step 1: Go to NetMap Road (transportation/Energy) Module > Road Drainage Diversion. In this tool, a user selects the road segment length scale and change in elevation in which to model the hydrologic connectivity of roads, and thus the concentration of flow. See the sensitivity analysis in the Tech Help. Future versions of this tool (later 2013) will allow users to import a shapefile of points, each piont indicating the location of actual drain points, including culverts, rolling dips, and water bars etc.

Options include a worse case scenario (using large changes in elevation [5m] over a distance of 300m), or more modest hydrologic connectivity (using small changes in elevation, < 0.5m). This tool must be run prior to using NetMap's road surface erosion tools. The tool assumes that all road-stream crossings function.