Application of geographic information system for soil and water conservasion in agricutural area: A case study of Bantha-Mai,Patong subdistric,Chantaburi province
Abstract:
Chanthaburi province has the suitable potential for agriculture, so erosion is an important problem in this area. A case study in the area of Ban Tha-Mai, Patong Subdistrict, Soidao District, Chathaburi Province was selected to study the impact of land degradation. The concept is to reduce soil loss in an agricultural land by using the Universal Soil Loss Equation (USLE) and Geographic Information System (GIS) for evaluating soil loss. USLE formular is five factors: Rainfall erosivity factor (R-factor), Sil erodibility factor (K-factor), Slope length and slope steepness factor (LS-factor), Cropping management factor (C-factor) and Conservation practice factor (P-factor). All factors are written in USLE formula as A = RKLSCP. In this study, USLE is used as the four models of soil loss in four cases: first, the landuse without soil and water conservation measures; second, the landuse with vetgetative measures control by constructing the contour band; and fourth, the landuse with mixed vetgetative and mechanical measures.Each model was evaluated by using 118 land farms totally 2,685.70 rais. The total volume of soil loss in the first model was 33,104.16 ton/yr or with the average of 12.33 ton/rai/yr. The second model was 14,279.52 ton/yr or with the average of 5.32 ton/rai/yr. The third model was 18,440.15 ton/yr or with the average of 6.87 ton/rai/yr. The ratios of soil loss in the cases of without measure : mechanical measures control: vetgetative measures control: mixed vegetative and mechanical measures control are 3.82 : 2.13 : 1.65 : 1.In the case of soil loss in only agricultural land of 1,893.31 rais, the total volume soil loss was 26,448.87 ton/yr or with the average of 13.06 ton/rai/yr in the first model; 9,666.21 ton/yr or with the average of 6.97 ton/rai/yr in the third model; and 5,179.66 ton/yr or with the average of 2.56 ton/rai/yr in the fourth model. The ratios of soil loss in the cases of without measure: mechanical measures control : vetgetative measures control : mixed vegetative and mechanical measures control are 5.11 : 2.73 : 1.87 : 1.The soil loss erosion class is classified into 5 levels: very slight, slight, moderate, severe and very severe. The result of erosion class in the cases of without measure and mechanical measures control are classified into level 5 or ver severe with the volume of soil loss more than 20 ton/rai/yr. But the cases of vetgetative measures control and mixed vegetative and mechanical measures control are classified into level 4 or servere with the volume of soil loss 15- 20 ton/rai/yr.On the comparasion of the volumes of the actual soil loss and that of the loss computed from USLE by collecting sediment from reservior in the same watershed are 2,527.87 ton/yr or with the average of 6.80 ton/rai/yr and 2,605.09 ton/yr or with the average of 7.01 ton/rai/yr. The results also revealed that the soil loss from the two methods is nearly equal with the difference only 3.07%