Sediment to River Channels

Step Wise Guide

Erosion

· What parts of my watershed are most likely to contribute sediment to rivers and cause water quality problems and impacts to aquatic habitat?

Not all areas of a watershed have equal opportunity to erode and 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 (e.g., surface erosion vs landsliding vs debris flow).

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 > Generic Erosion Potential and Shallow Landsliding. These tools have two types of predictions. Generic erosion potential and shallow landslide susceptibility that does not account for the delivery of sediment (and organic material, including large wood) to stream channels and the same two parameters but with delivery of sediment considered. Use the "delivery" option to identify which areas in your watershed have the highest likelihood of delivering sediment to streams.

Step 2: Go to NetMap Erosion Tools > Channelized Mass Wasting> Debris Flow. Use both reach and junction debris flow parameters to identify which headwater basins are most likely to delivery sediment to streams, and in particular fish bearing streams.

Step 3: Go to NetMap Erosion Tools> Sediment Delivery. This tool allows a user to select the channel gradient threshold associated with sediment delivery for the Generic Erosion and Shallow Landslide attributes. For example, a user might only be interested in sediment delivery to anadromous fish streams, and thus a threshold of about 10% would be selected. Or a user might be interested in all fish streams, including those with resident fish, and they would select a gradient threshold of about 20%. There are also three "proportion" grids that are located in the debris flow tool that are affected by running the delivery tool (refer to the debris flow tool to learn about the proportion predictions).

Step 4: Go to NetMap Erosion Tools > Surface Erosion. NetMap's surface erosion tool, both in its standard format and wildfire related versions, uses the WEPP disturbed technology. Available later summer 2013.