STUDY OF INFLUENCE OF LAND CLOSURE CHANGE ON HYDOLOGY CHARACTERISTICS IN KLOPOSAWIT SUB WATERSHED

• Main Author: Darmawan Pribadi, Arif
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/44102
• Institution: Institut Teknologi Bandung

The Sampean watershed (DAS) is located in East Java Province. The watershed with an area of around 1249 km2 stretches across 3 regencies, namely Jember, Bondowoso and Situbondo. The area of Sampean watershed in Bondowoso Regency is the largest, which is 11,009,935 hectares or 88.15% of the total area of Sampean watershed as a whole. Then the area of Sampean Watershed in Jember Regency is 59,703 hectares (0.47%) and in Situbondo Regency is 1,421,362 hectares (11.38%). Based on the existing observation discharge data, the location of the water level observation station is located in Taman Desa, Wonosari District, Bondowoso Regency with the name AWLR Kloposawit. The results of the delineation show the extent of influence of the Kloposawit AWLR in the Sampean watershed area, which is 61,635.95 hectares (616.35 Km2). So that in this study calibration of the discharge data of the simulation results and observations based on the catchment area of the Kloposawit Sub-watershed located in the upstream part of the Sampean watershed. The increase in flood events that occurred in Bondowoso and Situbondo Districts, shows that surface runoff has changed. Based on the explanation previously presented, it is necessary to conduct a study related to the effect of land cover changes on hydrological characteristics in the Sampean Watershed. As an effort to solve this problem by analyzing hydrological characteristics through the development of management patterns and land cover that can increase infiltration capacity and reduce surface runoff. Analysis of hydrological characteristics of watersheds that are affected by changes in land cover can be done using the hydrological model. One of the good hydrological models used is the SWAT (Soil and Water Assessment Tools) model. The application of the SWAT model is used to simulate changes in land cover to the hydrological characteristics of the Sampean watershed. So that it is expected to know the effect of changes in land cover on hydrological characteristics. The method used in this modeling is done by ArcSWAT. 2. From the analysis shows that the trend of daily record debit data tends to increase from 2002 - 2017. The maximum annual debit from 2002 - 2017 has an increasing trend with the highest maximum debit value occurring in 2013 (150.85 m3/sec), in 2008 ( 116.18 m3/sec), in 2011 (81.85 m3/sec). The sixteen year increase in discharge results was 4 m3/s. Whereas based on annual maximum discharge data for sixteen years an increase of 42 m3/s was obtained. Based on this, it can be interpreted that absorption capacity in the Sampean watershed is declining. An increase in surface flow (SUR_Q) in 2003 showed 582.60 mm increased to 618.24 mm in 2016. Surface flow increased by 35.64 mm (6.12%). An increase also occurred in total river water (WYLD) of 114.12 mm (8.08%). The decrease occurred in the base flow of 104.93 mm (26.46%), originally the base flow in 2003 amounted to 396.50 mm decreased to 291.57 mm in 2016. By using the spatial plan map, the CN composite value in the Kloposawit Sub Watershed is 68.98, while the existing condition in 2016 was 70.01. This means that the condition of land cover in the Sub Das Kloposawit in the existing conditions in 2016, has not been in accordance with the direction of the spatial plan map that has been set. The decrease in CN CN composite also resulted in changes in other hydrological characteristic parameters in the Kloposawit Sub-watershed such as surface flow, decreased total Q max river water, while the base flow and Q min increased. By using the map of land cover prediction results in 2021, 2026 and 2031 from the results of the analysis of trends in land cover data previously, it is known that the results of the SWAT analysis in 2021 with an average annual rainfall of 2357.29 mm / year, predicted runoff will run off 641.12 mm / year, base flow 231.41 mm / year, total river water 1533.92 mm / year, the maximum discharge that occurred was 69.95 m3 / s, minimum debit of 0.98 m3 / s, and CN composite value of 71.15. based on the projection trend in 2026 the value of CN is 72.99 and 2031 CN is 74.45 there is a tendency for an increase in surface flow. Total water in the river and an increase in Q max, this is in line with an increase in CN value as a result of changes in land cover that occur in the Kloposawit Sub-watershed. Large runoff shows the ability of soil infiltration in the Kloposawit Sub-watershed is decreasing.