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 low resolution grid	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 detailed impact of erosion on roads design of measures
Models	Spatially averaged SWAT Distributed RUSLE3D (simplified)	Distributed RUSLE3d USPED SIMWE	Distributed RUSLE3d USPED SIMWE

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:

see SWAT

3. 2 Installation scale distributed, low resolution (30-90m)

preparing the data:

DEM,
soils,
land cover,
rainfall,
prevention measures

RUSLE3D (simplified)

ArcGIS8
GRASS5

USPED (simplified)

ArcGIS8,
GRASS5

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

ArcGIS8,
ArcView3
GRASS5

USPED

ArcGIS8
ArcView3,
GRASS5

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

ArcGIS8
GRASS5

USPED

ArcGIS8
GRASS5

WEPP - access on-line version
analyzing, interpreting and presenting the results
planning applications

location, size and shape of protective vegetation areas
erosion on roads and its prevention

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