36 •
Use the map calculator to create new themes of the flow accumulation classification as 0 and 1.
• Use map calculator to compute the LS factor as shown below. Note that
the slope must be converted to radians from degrees by multiplying the slope by 3.14 pi and dividing by 180.
The technique for estimating the RUSLE’s LS factor that will be used here was proposed by Moore and Burch 1986a and 1986b. They derived an equation
for estimating LS based on flow accumulation and slope steepness. The equation is:
LS = Flow Accumulation Cell Size22.130.4 sin slope0.08961.3
Fig 3.5: The process of manipulate LS factor from DEM
3.6.4. Cover Management Factor C
C factor reflects the effects of vegetation cover on soil erosion, hence, this factor is often used to compare relative impacts of management options on
conservation plan. The land cover-management factor C is the most important in RUSLE because it represents conditions that can easily be managed to reduce
erosion Renard et al., 1994. The C factor reflects the effect of cropping and management practices on erosion rates. It indicates how conservation affects the
average annual soil loss and how soil loss potential will be distributed during cropping and other management schemes Renard et al., 1997. It is based on the
3.4
37 concept of deviation from a standard plot under clean continuous fallow
cultivations. In RUSLE, C is computed from soil loss ratios SLR i.e. prior land use PLU, canopy cover CC, surface cover SC and surface roughness SR.
In this study, a land cover type map was produced as the result of image classification of Landsat ETM+ Image. The C factor value can be ranked based on
the FAO standard tables see Appendix-15 given information about land use and management for land degradation assessment.
3.6.5. Land Conservation Factor P
The assign value of factor P as a attribute field according to FAO standard value and rating. Put the value of P as 1 for non-conservative area and
zero for conservative forest area. For Agricultural area, the P factor classification based on the agricultural practice, which is normally divided into: terraces
cropping, contour cropping, mulch cropping and permanent ground cover type. The table showed the P- factor classification for several conservation practices in
Indonesia Hammer, 1980 in Appendix-16.
3.6.6. Calculate the Erosion Rate
Using map calculator can estimate RUSLE soil erosion for every grid cell
in the area of interest. 3.7. Analysis the Model
In this research, propose to use analysis method with changed the parameter “land use and land cover” differencing between four landsat TM
images of different dates to compare the rate of erosion by soil loss in each district based on four different land used and cover characteristic from of scenario.
38
IV. RESULTS AND DISCUSSIONS
4.1. Land Cover Change Classification
The large areas of land cover are mapped at 1:50,000 scale using Landsat TM andor ETM data.
The land cover mapping was carried out using the FAO Land Cover Classification System LCCS, a new methodology especially created
for land cover mapping and now used worldwide. The following list describes the main phases applied in the present study, for the creation of the land cover maps:
1. Satellite data selection 2. Satellite data preprocessing
3. Satellite data classification 4. Satellite data interpretation and vectorization of the resulting units
5. LCCS classification 6. Field checking
7. Composition of final land cover maps
4.1.1. Satellite Data Selection
As previously indicated, all areas under study were used in July 1989 for a rapid assessment of local physiographic and of the main land cover classes
occurring there. Satellite data were selected on the seasonal based of the crop calendar for the main crops. Although the purpose of the study was to prepare
land cover maps and not crop inventories, it was considered of some importance to be able to separate the crops in the field at the time of satellite data acquisition.
Consequently, an image acquired in December is included in the wet season, while July and August and September are the dry season. Based on the seasonal
