COURT CREEK PILOT WATERSHED -
TOPOGRAPHIC ANALYSIS AND EROSION MODELING

Analysis of new 10m DEM

New 10m DEM has been received and it is being analyzed. 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 the hydrologic unit 102
location of the hydrologic unit 102 can be found on this picture

The new DEM has substantially more detail than the 30 m DEM which we have used before. While the total amount of water flowing out of the watershed would be the same, the new DEM shows that the flow from hillslopes and first order watersheds is much more in the form of concentrated flow rather than sheet flow predicted from 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 inthe final document)

• flow pattern derived from the original 30m DEM
• flow pattern derived from 20m smoothed DEM reinterpolated by RST from the 30m DEM
• flow pattern derived from the new 10m DEM
• flow pattern derived from the smoothed new 10m DEM

Low 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
• slope
• aspect
• Land use (from ILGIS CDROM - Derived from LANDSAT 1993) draped over terrain
• Land use draped over terrain (zoom in to show the resolution of the data)
• C-factor, very rough estimate based on the land use map and general published values
• Topographic erosion risk estimated by modified USLE LS-factor (as function of upslope area and slope) 
• 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 and we need to check with NRCS whether the average C-factor of 0.5 for row crop and 0.3 for small grains is correct.
• Locations with potential for high erosion estimated by modified USLE draped over digital elevation model - this image shows that the high risk areas are in locations where the flat upland terrain transitions into hillslopes but is not yet steep enough to have forest on it. In some locations there is small grain on rather steep slopes along the streams - creating a really high erosion risk, however this may be due to incorrect land use classification.
• Spatial distribution of net erosion/deposition estimated by USPED (very rough estimate - requires higher resolution)

Results for a link with the ISWS model

Note: there is a mismatch between the numbers for HU in our and ISWS data which has to be fixed

• 
  Hydrologic units (HU) for the ISWS model

• Soil loss estimates for the HU estimated as averages from the values computed for each 20m grid cell by modified USLE
• Total eroded soil for the the HU estimated as sum from the values computed for each 20m grid cell by modified USLE (no deposition was considered)
• Spatial pattern of land use HU 102 (52 in ISWS) which was identified by the models as high sediment source.
• Spatial pattern of erosion risk within HU 102 (52 in ISWS)

 Subwatersheds with high erosion risk in headwater areas

• Location within the watershed
• Land use
• Modified LS factor (includes areas with concentrated water flow and potential for gullies)
• Erosion risk estimated by modified USLE
• "Hot spots" with high erosion risk
• Potential for gully formation
• 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)

Analysis of topographic potential for wetlands

• "wet areas" represented by blue color, derived from simulated spatial distribution of potential water depth (without drainage through streams or channels), existing wetlands are shown in red
  view the 3D VRML map interactively
• locations with suitable topographic conditions for wetlands

Statistics/summaries for the upper Middle Creek from the data and preliminary erosion estimates at 10m resolution. (averages, totals, [%] areas ...)

• Scheyern farm: impact of land use alternatives (grassed waterways and contour strips)
• Impact of hedges
• Modeling for precision farming: terrain, soil properties, water and sediment

This project is supported by C-FAR IT-SRI and Illinois Department of Natural Resources

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