Landscape soil erosion modeling for spatial conservation planning: GIS-based tutorial

Prepared by Helena Mitasova, GMSL UofI, MEAS NCSU, Bill Brown GMSL UofI

1. Introduction

purpose, goal

2. Multiple scale approach

 2.1 Diagram for multiple scale approach


- with links to figures from Ft. Hood
 

Scale / unit		 FIGURE - installation region  FIG watershed FIG subwatershed/field 
Data Spatially averaged 
  • existing and planned use at hydrologic units level
  • polygon/vector data or 100-30m resolution
 Distributed
  • existing and planned use at grid level
  • 10-20m resolution or detailed polygons
 Distributed
  • existing and planned use including manmade features
  • 1-2m resolution raster + linear features/borderlines

Tasks
  • identification of high risk subwatersheds requiring detailed analysis and installation of measures
  • identification of large conservation areas
  •  hot spots in watersheds
  • prevailing erosion deposition pattern for given land use
  • location of conservation measures (dense vegetation, stream buffers, sedimentation ponds/constructed wetlands)
  • detailed erosion, deposition pattern including the effects of conservation measures
  • design of measures

 

2.2 Theory and algorithms used in the models

2.3 Runing the analysis in GIS

3. Notes on preparation of data

The data needed for erosion modeling are often already available from other projects and mapping efforts. Then simple checks of their suitability is sufficient and the methods outlined above can be directly applied. However, in some cases further processing of data is needed to extract the necessary parameters with sufficient accuracy and realism. It is impossible to address all issues that can arise so the focus of the next sections will be on the most common problems and approaches to solution.
 

3.1 Digital elevation model

Types of digital elevation data and their suitability for erosion modeling (link examples, any other types relevant to installations?): Finding the elevation data on Internet
Assessing the quality of DEM (include link/reference to Joe Wood's work)
Selecting the resolution
Reinterpolating, smoothing and stream enforcement(compare the estimates from integer and FP DEM)
Deriving the model parameters (algorithms, impact of resolution, relative importance (Gertner), comparison with field data (LCTA, NRC inventory):


3.2 Land use/land cover

USGS 30m landsat based data
New 1m vegetation maps (note of 10m resolution DEM used and uniform buffers along streams for bottomland forest
Estimating the C-factor for GIS-based data
Resampling to higher resolution - sharp versus smooth boundaries
Finding the land cover and C-factor data on the Internet

sources, resolution, level of detail - broad categories at 20-30m resolution, %vegetation cover for design at sites (1m resolution)

3.3 Soils

SSURGO data - K-factor based on soil map (polygons)
Continuous maps of soil properties - future trend
Soil data on Internet

3.4 Rainfall

Rainfall - r-factor - annual, monthly, storm - there are databases and maps with annual, monthly, storm and lot of other useful rainfall parameters - are these standard in installation databases -I will provide a reference (check it on the web)

Ft. Polk=400

Ft. Hood = 200

DEM -> slope, aspect, upslope area. Algorithms, impact of resolution, relative importance (Gertner), comparison with field data (LCTA, NRC inventory)

Land use -> C-factor, put a table here, write a function which will transform LU->C, are there any standard categories for LU at installations?, C-factor and LCTA and other field data - any projcets to link this with? (Steve mentioned combination of landsat and LCTA or field measurements to derive C. Use of NRCS inventory data, adding P-factor

Questions: are there standard LU/LC categories for installation GIS for which we can provide a base C-factor (which people can then adjust locally depending on the %cover)

Ssurgo - > K-factor, vector to raster, issues of continuity

exponents m, n
 

4. Notes on running the models

5. Notes on creating and analyzing the resulting maps

Continuous value maps - explain, legend, color tables
Class maps - reclassified, extreme, severe, high, medium, low, stable

Sumary statistics, reports:

histogram, report-%area from each class, average rate, total soil detached.....
 
 

6. Notes on applications for planning


Change laduse/implement conservation measure,...- installation wide, sub-installation-landscape scale

Minimize detachment and net erosion:
a)model based: set max detachment treshold - create new cover, (necessary C, suggested cover invertly derived from the table), set max net erosion treshold, set elimination of concentrated flow and other criteria

b)feature based: set buffers along the streams (uniform with given width, adjusted by model,..), set hedge along contour, grass filter strip, conservation area - compute necessary C and adjust shape,

applications manual: sequence of commands to find roads affected by high erosion risk wetland areas affected by high erosion
 
 

Deposit sediment: increase sedimentation rate in deposition area, create sedimentation pond, ....
Notes - for the management purposes there seems to be a need for categorization/classification - first streams, land are split into discrete homogeneous units and then they are classified/zoned for what we can do with them - is this the most effective approach??? (this results in uniform buffers, interactions between various landscape phenomena such as streams/topography ignored, etc. this also results in such observations that we have more sediment coming from the forested watershed that from agricultural/developed one.
 

Existing material to be plugged in

- USLE,USPED on-line tutorials

- GRASSBook erosion modeling
- preparation of data from reports and grassbook
- processing of results from grassbook and reports

Notes/questions

Standardized filed names (e.g. used in ATTAC document) - is there any official list for that?
Standardized categories for erosion rates severe/high/moderate/low/stable
Standardized color tables for inputs and outputs

work on planning applications with Rich and Dan.