RATE ANALYSIS OF SOIL EROSION USING UNIVERSAL SOIL LOSS EQUATION (USLE) METHOD IN JENEBERANG WATERSHED

Erosion in a watershed is a complex phenomenon that affects the quality of land resources due to either natural or human influence. The purpose of this study to determine the rate of erosion in the Jeneberang watershed and produce a recommendation of soil conservation to reduce the rate of erosion. This study uses some parameter maps, such as Rain Erosivitas Index (R) map, Land Erodibility Index (K) map, Length and Slopes Declivity Factor (LS) map, and Plants Management Factor and Soil Conservation (CP). All parameters were analysed using USLE map to determine the rate of erosion. The analysis results the rate of erosion by USLE method indicates the hazard level of the erosion in the Jeneberang watershed are dominantly at the very low levels with an area 55.068,39 ha or 71.6% of the research area. However, the erosion in the study area can not be ignored because there is a very high level of danger to the extensive erosion 11.681,55 or 15% of the research area. Therefore, generated a recommendation of soil conservation by soil cover planting and terrace construction repairs. By this conservation recommendation, the area with a high level of the rate of erosion reduce in the amount of 10,6%.


ISSN: 2320-5407
Int. J. Adv. Res. 10(02), 529-537 530 This study aims to apply GIS to predict the rate of erosion and the level of danger using the USLE method and provide recommendations for soil conservation as an effort to reduce the danger of erosion, especially in the Jeneberang watershed.

Research Method:-
The research location covers the entire Jeneberang Watershed which is geographically located at 119 o 23' 50'' BT -119 o 56'10'' BT dan 05 o 10'00'' LS -05 o 26'00'' LS. The data used are secondary data in the form of topographic maps sourced from DEM-SRTM, soil maps sourced from BAPPEDA of South Sulawesi Province, soil conservation maps sourced from Londongsalu research in 2008, vegetation cover maps sourced from Landsat Image 8 of 2016 and rainfall data sourced from BMKG Year 2012-2016. The analysis technique uses an overlay technique, which is to perform a spatial analysis by stacking thematic maps. Erosion estimation was carried out using the USLE method with the following equation (Bergsma et al., 1996): = . . . . . Notation, A = amount of erosion (tons/ha/year), K = soil erodibility value, R = rain index, L = slope length factor, S = slope factor, C = soil management factor, P = soil conservation action factor.
Factors R, K, L and S mathematically can be categorized as variables that cannot be changed. In other words, to reduce erosion can only be done by manipulating the values of C and P. The magnitude of the erosion hazard is grouped as in table 1.  Bergsma et al. 1996) Result and Discussion:-

Prediction and Mapping of Erosion and Hazard Level a. Rain Erosivity
Rainfall data was obtained from BMKG Station Region IV Makassar from 2012 to 2016 which consisted of 10 rain posts. Based on the data, it is known that the maximum average rainfall is 4,107.2 mm and the minimum average rainfall is 878.4 mm. It was also found that the highest rain erosivity index value occurred at the Malino rain post, which was 3,560.81 mm and the lowest was at the Pattalassang rain post at 662.84 mm ( Table 2). The high erosivity index (R) value is caused by the high annual average rainfall and the amount of rain intensity which is reflected in the high maximum rainfall at the rain post. 2.608,61 The R value obtained is the R value for each rain post. Therefore, to determine the R value for each pixel in the study area, interpolation was carried out using the Spline method. The map of the interpolation results can be seen in Figure 1.

b. Soil Erodibility
The soil type map in the research area consists of Andosol, Latosol, Mediterranean Reddish Brown, Reddish Brown Latosol Complex and Gray Brown Alluvial. The dominant soil type is the Reddish Brown Latosol Complex with an area of 42,000 ha (Table 3). Soil erodibility values in the Jeneberang watershed range from 0.09 to 0.28 which can be seen in Table 3 and Figure 2.

c. Long and Slopes (LS)
In the study area, the domination of the slopes is 0-8% with an area of 63,460 ha. The largest LS index value is 9.50 with a slope of >40 has an area of 5,396 ha (Table 4) and the distribution of LS values can be seen in Figure 3.   In the research area, the largest crop management value was on upland/field land use, namely 0.7 with a soil conservation value of 0.4 which has an area of 9,135 ha. The distribution of plant management values can be seen in Figure 4 and the distribution of soil conservation index values can be seen in Figure 5.

e. Erosion Mapping and Its Hazards
The results of the analysis of the erosion hazard level of the Jeneberang watershed can be seen on the ErosionHazard Level (TBE) distribution map in Table 6 and Figure 6. The table above shows that the erosion hazard level in the dominant Jeneberang watershed is still very low with an area of 55,068.39 ha or about 71.6% of the total area of the Jeneberang watershed. This shows that the erosion caused is not too large because the factor of plant cover and management is still quite good, but it cannot be ignored because it is also very high with an area of 11,681.55 ha. If plant management factors and conservation practices in the research area are not improved, the erosion rate that occurs in the future can become dominantly high or very high. Therefore, it is necessary to make recommendations for soil conservation that can reduce the rate of erosion that occurs so that the resulting erosion is not too large.

Conservation Recommendations
In this study, soil conservation recommendations are focused on very high levels of erosion. The estimated C values and P values for the conservation recommendations used can be seen in table 7.  The recommended conservation recommendations to be applied to the Jeneberang watershed are forests that previously without conservation measures were converted into forests planted with plantation crops with a dense ground cover, and some land uses that previously had poor bench terrace construction became better bench terraces.
The existence of conservation recommendations in the research area, there is a decrease in the rate of erosion so that areas that previously had a very high level of erosion hazard became areas that had a low level of erosion hazard. It can be seen in table 9 that the percentage of areas that have high erosion experienced a change of 10.6%, namely the percentage before the recommendation was 15% and after the recommendation was 4.4%. The map after the conservation recommendations can be seen in Figure 8

Conclusion:-
The erosion rate using the Universal Soil Loss Equation (USLE) method shows the erosion hazard level that occurs in the dominant Jeneberang watershed is at a very low level with an area of 55,068.39 ha or 71.6% of the research area.
Recommended soil conservation, namely planting dense cover crops and improvement of terrace construction. With this conservation recommendation, areas with very high erosion rates experienced a change of 10.6%, from 15% to 4.4%.