Erosion depends on USLE factors A, Average Anual Soil Loss=RKLSCP where:
R = rainfall erosivity index
K = soil erodibility factor
L = topographic factor, L for slope length
S = topographic factor, S for percent slope
C = a cropping-management factor
P = conservation practice factor
Having high rainfall thus R factor contribute significant amount of erosion . Example R factor of Brunei is 178.3164 maximum will be 282.8185 as average rainfall is 2873.9 and maximum rainfall 4000mm.
Thus Erosion Class is divided :
1. Less 1 ton per anum
2. >1- 10 ton per anum
3.>10-50 tons per anum
4>50-100 tons per anum
5 > 100 ton per anum
Erosion risk map can be prepared basing on soil series for their erodibility factor K or from calculation depending on texture and organic matter. Problem aries for Brunei ADA soil map are three. One is the soil textures data classification by Hydec as by CIERO do not match USLE textures for culculation of M one of the component in K culculation.This need a tedious reculculation and reestimation to match USLE classification. Organic matter estimation method must be the same as USLE method. If there some different proper correlation is needed.
The other factor is the soil boundry made by CIERO misalligment with the terrain beside some location the soil map do not match after field check. This will result in eror when soil erosion map is prepared.
Task to prepare Soil Erosion Map GIS application can be divided into the following phase:
1. Indentifying Google Map/ Land use to allign with project area
2. Digitised contour over lay
3. Digitised soil map overlay and correct misalligment
4. Logical extropolation of soil boundries in association map units
5. Measuring map slope base length and culculation to derive actual length
6. Culculation of Slope gradient from base length and contour height different
8. Digitised terrain class map base on derived LS factor(slope length and slope gradient)
9.Data processing Hydec textures an CERO data conversion to USLE textures
10. Weighted average of all profiles (CIERO & Hydec) for culculation of M value to derive K values
11. Organic matter culculation from organic carbon and weighted average of OM to derive M for K culculation
12. K Value check and counter check using Malaysian Similar Soils
13.Using Namograph to get K Values
14. Culculation of Annual soil loss using USLE with assume factor C, Crop and factor P.( Forest ,Various Crops,Various management)
15.Finalised Soil erosion 4 type map for each project Risk map base on Forest,Perenials,Annuals,Vegetables
