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 Look-up table for multiple scale approach
Designed for quick access to the relevant parts of the tutorial
the table will have links to the topics/documents needed to fulfill the
given task (change the order to tasks, data,models)
Scale / unit |
FIGURE - installation region |
FIG lanscape/watershed |
FIG subwatershed/field |
| Data |
Spatially averaged
-
existing and planned use at hydrologic units level
-
polygon/vector data or 100-30m resolution
Distributed
|
Distributed
-
existing and planned use at grid level
-
10-20m resolution data 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
|
| Models |
Spatially averaged
-
SWAT
-
Distributed
-
RUSLE3D (simplified)
|
Distributed
|
Distributed
|
2.2 Theory and algorithms used in the models
-
Briefly explain the fundamentals and provide links to detailed papers and
reports
-
Erosion processes - sheet, rill, gullies, stream:banks/bed (link photos
from installations - may I use Steve's?)
-
Erosion regimes: from detachment to transport capacity limited (animation?)
-
Models: from empirical, spatialy averaged to process-based, distributed
-
Implementations: RUSLE -> RUSLE3D, USPED, WEPP->SIMWE
3. Runing the analysis in GIS
-
3. 1 Installation scale spatially averaged modeling:
-
3. 2 Installation scale distributed, low resolution (30-90m)
-
preparing the data:
-
DEM,
-
soils,
-
land cover,
-
rainfall,
-
prevention measures
-
RUSLE3D (simplified)
-
USPED (simplified)
-
analyzing, interpreting and presenting the results:
-
maps with continuous values,
-
maps with categories,
-
maps of hot-spots,
-
maps of erosion status indicators (see Hohenfels)
-
summary reports and histograms
-
Planning applications
-
roads under risk of increased sedimentation and damage by erosion
-
wetlands, ponds and lakes with high risk of unsustainable sedimentation
-
training areas requiring increased maintance or redesign
-
...
-
3.3 Lanscape/subwatershed scale, moderate resolution (10-20m)
-
preparing the data
-
RUSLE3D
-
USPED
-
analyzing, interpreting and presenting the results
-
planning applications
-
identification of high erosion risk hot spots including concentrated flow
erosion
-
eroding roads
-
stream buffers
-
vegetation planning for reduction of sediment delivery into wetlands
-
....
-
3.4 Small watershed/field/design scale, high resolution
-
preparing the data
-
RUSLE3D
-
USPED
-
WEPP - access on-line version
-
analyzing, interpreting and presenting the results
-
planning applications
-
location, size and shape of protective vegetation areas
-
3.5 Modeling with spatially variable resolution:
-
finite element/finite difference meshes (WMS)
-
path sampling and nested grids (SIMWE)
4. 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.
4.1 Digital elevation model
-
Types of digital elevation data and their suitability for erosion modeling
(link examples, any other types relevant to installations?):
-
USGS DEM,
-
IFSARE,
-
LIDAR,
-
Digital photogrammetry (points/TIN, contours)
-
Rapid kinematic survey data
-
Ground survey
-
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, comparison with field data (LCTA, NRC inventory):
-
slope,
-
aspect (direction of flow)
-
upslope area (steady state water flow)
4.2 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)
4.3 Soils
-
SSURGO data - K-factor based on soil map (polygons)
-
Continuous maps of soil properties - future trend
-
Soil data on Internet
4.4 Rainfall
Rainfall - R-factor - annual, monthly, storm
5. Notes on running the models
-
5.1 Selecting the level of detail, resolution and appropriate model
-
5.2 Selecting the model parameters (exponents)
-
5.3 Trouble shooting -
-
treating unrealistic erosion rates,
-
avoiding/fixing noisy results
-
checking for artificial patterns
-
5.3 Calibrating the model (future?, data are needed for this)
6. Notes on creating and analyzing the resulting maps
6.1 Continuous value maps - what they mean, legend, color tables (automatic
creation of exponential legend with intesity given by parameter p=0.01,
colors see Cebecauer/GRASScurvatures for erosion/deposition)
6.2 Class maps - reclassifying the continuous maps, standardized classes
6.3 Sumary statistics, reports:
histograms,
%area from each class,
average rate,
total soil detached, total net soil loss, ...
7. 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.
Link-in the following material (some need modifications)
- 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