1. GIS-Assisted Approach in Soil Erosion Assessment using Manifold Software

2. Introduction
Soil erosion research is a capital-intensive and time-consuming activity.
However, the advent of computer technology leads to a new approach in dealing with soil erosion in a watershed.
GIS has the capability of integrating spatial and analytical functionality of spatially distributed data.

3. Introduction Soil Erosion Types of Soil Erosion
The removal of soils from their original site
Removes top fertile soil
Source of sediment that pollutes streams and fills reservoirs.
Contributes to non-point source pollution.
Composed of three subprocess (detachment, transport and deposition)
Types of Soil Erosion
Sheet erosion
Rill erosion
Gully erosion
Stream channel erosion

4. Soil Erosion Models Universal Soil Loss Equation (USLE)
Empirical model
Estimates soil erosion by raindrop impact and surface runoff
Modifield Soil Loss Equation (MUSLE)
Revised Universal Soil Loss Equation (RUSLE)
WEPP
Rose Erosion Model
CREST
Others

5. What are the Factors of USLE?
Critical Factors
The critical factors affecting soil erosion were based on the empirical formula developed by Wischmeir and Smith (1978) widely known as USLE.
Erosive power of rainfall (R)
Soil erodibility (K)
Topographic Factor (LS)
Vegetative cover (C)
Erosion measures (P)

6. Universal Soil Loss Equation
The USLE is expressed by the formula with some modifications:
A = R * K* L*S * C * P
where:
A = Annual soil loss
R = Erosivity
(EI30 = Rm)
K = Erodibility
(K = [(0.043pH)+(0.0621/OM)+(0.0082S)-(0.0062C)]Si
L = Slope length factor
S = Slope gradient factor
C = Cover factor
P = Erosion control factor

7. The Factors of USLE ….

8. The Factors of USLE ….

9. The Factors of USLE ….

10. The Factors of USLE ….

11. The Factors of USLE ….

12. The Factors of USLE ….

13. The GIS-Assisted Approach
(using USLE)

14. The GIS-Assisted Model …

15. GIS-Assisted Approach in Soil Erosion Assessment
Here is the simplified procedure in calculating areas vulnerable to soil erosion of the sample watershed:
Generation of Input Maps as Drawing using Manifold
Commands: Generate of thematic maps (areas, lines and points) affecting soil erosion following the procedures described in the previous topics (either from a georegistered scanned image and then proceed with digitizing; or by using the GPS readings and create a table and then create a drawing from the table). In the example, the following are considered: a) contours, b) soil map, c) landuse map (vegetation and erosion control practices), and d) rainfall erosivity from different stations.
Commands: Press File  Create  Drawing….. R Isohyte Map … K Map … LS Map … C Map … P Map

16. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
LS Factor
Generate a Surface from Contours (DEM)
Commands: Right click on the drawing (with contours) and press Copy. In the Project Pane, right click and select Paste As  Surface, then a Paste as Surface Dialog Box will appear. Input Height as Elev, Type as Floating-point (single), Pixel Size as 10 or higher depending on the size of watershed, and Method as Triangulation (flat), and press OK. In this example, 10 x 10 pixel size is used.

17. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
LS Factor
Generate the LS Factor from Slope
Commands: Select any Surface Component in the Map and press Surface  Transform and a Transform Dialog Box will appear. Press the pull down menus for Scope and select All Pixels. In the Formula Field, use this formula to compute for LS Factor:
LS = (Ls/22.13)0.5*( s s2)
(pow((10/22.13),0.5))*(0.065+(0.045*(slope(DEM)))+(0.0065*(pow((slope(DEM)),2))))

18. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Soil Erodibility (K)
Add a Column in the Table for Erodibility Values
Commands: Double click the Table component (Soil Map) in the Project Pane. Then, right click on the column of the Table and press Add  Column and the Add Column Dialog Box will appear. Type the Name (K values) and Type (Floating-point (double)) of the column and press OK. Input the K values and these will depend on the nature of soil.

19. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Soil Erodibility (K)
Generate a Surface from Soil Map with K Values
Commands: Right click on the Drawing (Soil Map with K values) in the Project Pane and press Copy. In the Project Pane, right click and select Paste As  Surface, then a Paste as Surface Dialog Box will appear. Input Height as K values, Type as Floating-point (double), Pixel Size as 10 or higher depending on the size of watershed, and Method as No Interpolation (default), and press OK. In this example, 10 x 10 pixel size is used

20. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Cover Factor (C)
Add a Column in the Table for C Values
Commands: Double click the Table component (Landuse Map) in the Project Pane. Then, right click on the column of the Table and press Add  Column and the Add Column Dialog Box will appear. Type the Name (C values) and Type (Floating-point (double)) of the column and press OK. Input the C values and these will depend on the nature of landuse/vegetation cover.

21. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Cover Factor (C)
Generate a Surface from Landuse Map with C Values
Commands: Right click on the Drawing (Landuse Map with C Values) in the Project Pane and press Copy. In the Project Pane, right click and select Paste As  Surface, then a Paste as Surface Dialog Box will appear. Input Height as C Values, Type as Floating-point (double), Pixel Size as 10 or higher depending on the size of watershed, and Method as No Interpolation (default), and press OK. In this example, 10 x 10 pixel size is used

22. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Erosion Control (P)
Add a Column in the Table for P Values
Commands: Double click the Table component (Landuse Map) in the Project Pane. Then, right click on the column of the Table and press Add  Column and the Add Column Dialog Box will appear. Type the Name (P values) and Type (Floating-point (double) of the column and press OK. Input the P values and these will depend on the nature of erosion control measures.

23. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
Erosion Control (P)
Generate a Surface from Landuse Map with P Values
Commands: Right click on the Drawing (Landuse Map with P values) in the Project Pane and press Copy. In the Project Pane, right click and select Paste As  Surface, then a Paste as Surface Dialog Box will appear. Input Height as P values, Type as Floating-point (double), Pixel Size as 10 or higher depending on the size of watershed, and Method as No Interpolation (default), and press OK. In this example, 10 x 10 pixel size is used

24. GIS-Assisted Approach in Soil Erosion Assessment
Generation of Surfaces from Drawings of Factors using Manifold as Input to Soil Erosion VA
R Isohytes (R)
Generate Surface from Rainfall Amount Map
Commands: Right click on the Drawing (Rain Station Map with R values) in the Project Pane and press Copy. In the Project Pane, right click and select Paste As  Surface, then a Paste as Surface Dialog Box will appear. Input Height as R values, Type as Floating-point (double), Pixel Size as 10 or higher depending on the size of watershed, and Method as Kriging, and press OK. In this example, 10 x 10 pixel size is used.

25. GIS-Assisted Approach in Soil Erosion Assessment
Calculation of Areas Vulnerable to Soil Erosion
Calculate the Soil Erosion Vulnerability
Commands: Select any Surface Component in the Map and press Surface  Transform and a Transform Dialog Box will appear. Press the pull down menus for Scope and select All Pixels. In the Formula Field, input the following:
([R Isohyte Factor])*([K Factor])*([LS Factor])*
([C Factor])*([P Factor])

26. Thank you