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Water Resources
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Subwatershed Prioritization for Watershed Management
using Remote Sensing and GIS
4.4. Prioritization Analysis
As discussed earlier, the DSI, SI and PC were taken as the condition and used for the prioritization analysis by simple matrix method. To create this matrix, the range of quantitative value has been defined for qualitative value. Table 3 shows the qualitative for DSI, SI and PC.
Table 3 Rating the Condition Indicator
| Rating |
DSI |
SI |
PC |
| Very Low |
<1 |
- |
- |
| Low |
1 to 4 |
<0.1 |
<7 |
| Medium |
4 to 6 |
0.1 to 0.5 |
7 to 15 |
| High |
6 to 8 |
0.5 to 2 |
15 to 30 |
| Very High |
>8 |
>2 |
>30 |
From the qualitative rating, the two-dimensional overlay matrix has been created by taking two indicators at a time. First the matrix analysis between DSI and SI had been done and they were grouped into 5 classes, which were used for second matrix analysis with PC. Lastly they were again grouped into five qualitative classes (Table 4). The group has been decided on the basis of the logical combination of the indicators. For example, the combination of high DSI and SI were grouped as first priority group. The output of the matrix analysis is given in Table 5, where all twenty-two subwatershed were classified in five group. Map 3 shows the spatial distribution of the subwatershed for conservation prioritization work.
Map 3: Conservation Prioritization Map of the Trijuga Watershed, Nepal
Table 4: Prioritization by Matrix Analysis with DSI, SI and PC.
| SI/DSI |
VL |
L |
M |
H |
VH |
|
PC/DSI-SI |
VL |
L |
M |
H |
VH |
| L |
5 |
5 |
4 |
3 |
2 |
L |
5 |
5 |
4 |
3 |
2 |
| M |
5 |
4 |
3 |
2 |
2 |
M |
5 |
4 |
3 |
2 |
2 |
| H |
4 |
3 |
2 |
1 |
1 |
H |
4 |
3 |
2 |
1 |
1 |
| VH |
3 |
2 |
1 |
1 |
1 |
VH |
3 |
2 |
1 |
1 |
1 |
VL= Very Low, L=Low, M=Medium, =High, VH=Very high
12,3,4 and 5 are the Priority Decreasing order |
Table 5: conservation Prioritization of the Subwatersheds
| Conservation Prioritization |
List of the subwathershed |
| Fist Priority |
Chhaude-khola, Puwar-khola, Upper-Trijuga, Baruwa-Khola and Duwar-khola |
| Second Priority |
Adheri-khola, Lava-khola, shahi-khola, Lalpatta-khola and Pharse-khola |
| Third Priority |
Lower-Trijuga, Khajuri-khola and Bagha-khola |
| Fourty Priority |
Hadiya-Khola |
| Fifth Priority |
Deojor-khola, Kali-khola, thadi-khola, Khang-khola, Babiya-khola, Lohale-khola, Siwai-Naid and Ghiyar -khola |
5 Recommendations
Conservation work in the Trijuga watershed area should be started according to the priority list of Table 5. Slope stabilization, slope failure protection, gully control by check dam, reforestation, growing of horticultural crop along with some other intensive soil conservation activities are required for the first ranking subwatersheds. Fifth ranking subwatershed need little attention like maintaining the crown cover and protection of the existing forest along with managed agriculture. Other subwatersheds should be treated by intermediate activities according to their ranks.
6 Conclusion
Delineating the wathershed area into subwatershed for priority based conservation work is essential and appropriate for the developing countries like Nepal. Considering its drainage system can do such delineation. The delineated subwatersheds were used for prioritization. Prioritization can be done by considering their forest loss, soil loss and land sensitivity, which is defined as the locational relationship between forest loss and soil loss. These factors were used to extract the DSI, SI and PC, which were considered as the condition indicator of the subwatershed. Using these condition indicators, a new method of prioritization for conservation work was proposed by the qualitative matrix analysis. Based on prioritization, subwatershed conservation management activities were proposed. Finally, it can be said that remote sensing and GIS in combination with USLE model can be used as appropriate tools for subwathershed prioritization.
Reference
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