Modeling erosion and deposition pattern for a small watershed and comparison with the Cs distribution

Helena Mitasova, Bill Brown, Lubos Mitas
University of Illinois at Urbana-Champaign

Copyright © 1999 Helena Mitasova and Lubos Mitas

DEM with gully

Erosion/deposition by USPED: VRML

Erosion/deposition from Cs

1. Computation of DEM from survey data and topographic analysis

Location of the study area size of the study area: 31.5 acres

• Given data and a 2.m resolution DEM interpolated by the RST
  
• DEM with detailed representation of gully including the fault, interpolated by RST
  
• Comparison of contours from DEMs interpolated by RST with and without a fault line (black, brown). This is just to demonstrate the capabilities to create DEMs with faults using the RST and GIS tools. The smooth model without the fault was used in the erosion modeling and analysis which follows.
• slope
  
• aspect
  
• profile curvature
  
• tangential(contour) curvature
  
• slope length
  
• upslope area
  

2. Cover and soil data

• raw 2.5m resolution IFSAR DEM with imagery draped over it, no vertical exaggerration
  
• cfactor based on imagery (not yet used in computations)
  
• cfactor based on soil type
  
• kfactor
  
• slope length averaged for each soil type
  

3. Erosion modeling and Cs distribution

The following data were used for rainfal, soil and cover properties:
R=160,
C=0.2, K=0.17 on ridge (short grass with 20% cover, Brackett soil),
C=0.04, K=0.32 in the valley (short grass with 60% cover, Slidel and Topsey soil)

• Erosion/deposition estimated/modeled from the Cs data
  

  USLE

• USLE based on averaged K,C,L, only S is variable
  USLE based on averaged K,C,L,S for each soil type
  USLE based on averaged L for each soil type, S is variable
  
• USLE based on variable L computed by r.flow
  
• modified USLE based on upslope area
  

  USPED

• USPED with water term exponent p=0.6, slope exp=1.6 (many small events)
• USPED with water term exponent p=1
• USPED with water term exponent p=1.6, slope exp=1.6 (large event)
  USPED with water term exponent p=1.6, slope exp=1.3 (large event)
• USPED average of many small events and few large events

Totals and averages

Area with erosion and deposition

|-------------------------------------------------------------------|
|MAP: Cs                                                            |
|-------------------------------------------------------------------|
|        Category Information               | cell|   %  |          |
|description                                |count|  area|     acres|
|-------------------------------------------------------------------|
|erosion. . . . . . . . . . . . . . . . . . |22983| 71.91|      22.7|
|deposition . . . . . . . . . . . . . . . . | 8978| 28.09|       8.8|
|-------------------------------------------------------------------|
|TOTAL                                      |31961|100.00|      31.5|
+-------------------------------------------------------------------+

|-------------------------------------------------------------------|
|MAP: USPED p=0.6
|-------------------------------------------------------------------|
|        Category Information               | cell|   %  |          |
|description                                |count|  area|     acres|
|-------------------------------------------------------------------|
|erosion. . . . . . . . . . . . .. . .. . . |18974| 59.37|      18.7|
|deposition . . . . . . . . . . .. . .. . . |12976| 40.60|      12.8|
|-------------------------------------------------------------------|

|-------------------------------------------------------------------|
|MAP:  USPED p=1.0
|-------------------------------------------------------------------|
|       Category Information                 | cell|   %  |         |
|description                                 |count|  area|    acres|
|-------------------------------------------------------------------|
|erosion. . . . . . . . . . . . . . . . . . .|23711| 74.19|     23.4|
|deposition . . . . . . . . . . . . . . . . .| 8239| 25.78|      8.1|
|-------------------------------------------------------------------|


|-------------------------------------------------------------------|
|MAP: USPED p=1.6                                                   |
|-------------------------------------------------------------------|
|      Category Information                 | cell|   %  |          |
|description                                |count|  area|     acres|
|-------------------------------------------------------------------|
|erosion. . . . . . . . . . . . . . . . . . |26055| 81.53|      25.7|
|deposition . . . . . . . . . . . . . . . . | 5892| 18.44|       5.8|
|-------------------------------------------------------------------|

Results to be added: USPED for terrain without gully, SIMWE simulations(impact of diffusion with different weights, simulations over fault)

Data courtesy NRCS Texas and Steve Warren, Colorado State University.