Surface Erosion

Step Wise Guide

Erosion

· Where is the highest surface erosion potential with a high likelihood of sediment delivery to streams and rivers?

Not all areas of a watershed have equal susceptibility to surface erosion and to deliver sediment to stream channels. Connectivity between hillsides and river channels is controlled by topography, the location of the river in proximity to hillsides, valley morphology and the type of erosion involved. For surface erosion, the lower the gradient of the land between the steeper hillside and the stream channel, and the greater the distance between the two landforms, the less erosion is delivered to the stream.

When working with NetMap's Erosion Tools, please refer to the "Warning" button in the tool interface. Follow up any remote sensing work, including using NetMap, with field work to verify environmental conditions and landslide and debris flow risk. There is never zero risk, there is only degrees of risk, which often is best considered on a relative basis.

Step 1: Go to NetMap Erosion Tools > Hillslope Surface Erosion-Veg/Fire. Using WEPP technology, users can characterize the surface erosion and sediment delivery characteristics of either their entire watershed or only a portion of it (the tool runs faster if only a small portion of the watersheds are selected - use the selection tool in Arc and select only those stream segments or tributaries of interest). The WEPP model in NetMap uses drainage wings to make predictions of surface erosion potential. Information on vegetation (or fire severity) and soils, as well as climate, is necessary to run WEPP Disturbed.

Optional Steps

Step 2. Go to Basic Tools > Risk Analysis > Stream Segment Overlap. Use this tool to quickly locate the stream segments, and associated adjacent hillslopes, with the highest (or lowest) erosion potential, in increments of percentiles (e.g., the top 1%, top 5%, top 10% etc.).

Step 3. Go to Basic Tools > Subbasin Classification > Sort and Rank. If the surface erosion analysis was done over a large part of the watershed or the entire digital landscape dataset, use the Sort and Rank Tool to classify erosion potential from highest to lowest at the scale of 12 digit, HUC 6th field subbasins.