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  Using Soil Erosion Modeling for Improved Conservation Planning: 
A GIS-based Tutorial

 

Court Creek Pilot Watershed -
TOPOGRAPHIC ANALYSIS AND EROSION MODELING

 

Lower resolution (20m/10m) analysis aimed at land use management at a regional/watershed scale

DEM (20m resolution derived from 30m DEM USGS), streams, roads and wetlands
C-factor, very rough estimate based on the land use map and general published values
Spatial distribution of erosion risk estimated by modified USLE
Locations with potential for high erosion estimated by modified USLE - the total area is 10,000 acres, which is about 16% of total Court Creek watershed. These areas have a potential to produce 87% of soil loss. Most of this soil is deposited before it can reach the streams. The high risk areas are mostly located between the flat upland and forested areas along the streams, on row crop and grain fields. The spatial extent and rates may be overestimated because no prevention measures were considered.

 

Analysis of new 10m DEM

Analysis of soil detachment and erosion/deposition patterns was performed using a 10m DEM (see discussion about its problems below). The patterns were simulated for the hydrologic unit 52 for the following scenarios: bare soil, corn, corn+60ft stream buffer, corn+100ft stream buffer, corn+60ft stream buffer+forest on slopes steeper than 10%, current (1993) land use, corn + protective areas (dense grass, forest) in locations with detachment rate higher than 10t/ay. The results (maps and numbers) are organized in a TABLE and include some comments and suggestions.

There seem to be waves along contours which may cause problems for erosion/deposition modeling, if these waves are artificial:
3D view of terrain within hydrologic unit 102
Hydrologic unit 102 can be found along the bottom of this picture

 

The new DEM has substantially more detail than the 30 m DEM.  Although the total amount of water flowing out of the watershed would be the same, the new DEM shows that the flow from hill slopes and first order watersheds occurs more in the form of concentrated flow rather than sheet flow predicted using the 30m DEM. The following figures show the flow patterns derived from the DEMs that we have been using (note these are draft pictures and will be replaced by more consistent ones in the final document)
flow pattern derived from the original 30m DEM
flow pattern derived from the smoothed new 10m DEM

 

 Sub-watersheds with high erosion risk in headwater areas

Detailed analysis of a sub-watershed was performed using the same data as the analysis for the entire watershed. The original DEM was re-interpolated and smoothed from 30m resolution to 10m resolution to get better representation of terrain geometry, however, no new information was added. The results of the erosion/deposition model indicate that there is some limited potential for deposition within the less protected headwater areas. This indicates that while farmers may be losing some soil there, part of the eroded soil moves only for a short distance. Further modeling and analysis needs to be performed to estimate how much sediment can be delivered to streams and whether more protection in these areas could have any substantial impact on water and sediment flow downstream.
Location within the watershed
Land use
Erosion risk estimated by modified USLE
Net erosion/deposition estimated by USPED with the exponent p=1.6 (typical for prevailing rill erosion)
Net erosion/deposition estimated by USPED with the exponent p=1.0 (prevailing sheet erosion)


More details

Up
Hohenfels Example
Camp Shelby extension
Court Creek Pilot Watershed
Court Creek Erosion  Example
Simulation of land use impact on erosion and deposition using SIMWE
Interpolation and simulation of terrain development with hedges

HOME                                                        H. Mitasova, et al.,  Geographic Modeling Systems Lab, UIUC