Judul: An Approach to Water Resource Management through Land Use Planning in the Way Besai Watershed in Lampung Province
Abstrak: Land use changes may have an impact on the decrease in water supply. In the meantime, water demand keeps increasing along with the increase in population and economic activities. The Way Besai Watershed, covering an area of 44 720 ha, plays an important role in providing water resources. Therefore, to ensure the sustainability of the water resources, there should be a good land use planning, particularly in relation with the efforts to protect the forest areas. This research, which was conducted in the Way Besai Watershed in 2013, aimed: (1) to find out the water supply and demand, (2) to assess water balance in terms of the supply and demand, (3) to formulate recommendations for the best land use planning, and (4) to study the economic value of the water resources. The total water demand by households, livestock activities, rice fields, and hydropower (PLTA) was calculated. Similarly, the water supply was calculated based on surface runoff using various mathematical equations. Next, SCS Model was used in the formulation of different scenarios of land use planning. Scenario 1 described the existing biophysical condition of the Way Besai Watershed. Scenario 2 was related to the land management by accommodating community activities in the forest through HKm by applying an agroforestry planting pattern. Scenario 3 was the combination Scenario 2 and the forest rehabilitation outside HKm area. Scenario 4 was the combination of scenario 3 and the efforts to change the pattern of coffee cropping monoculture. The best recommendation scenario for land use planning was selected based on hydrological as well as economic aspects using benefit and cost ratio (BCR). The water need of the Way Besai Watershed in 2011 was 441 450 909 m3/year, and it could still be fulfilled by the water supply amounting to 460 452 600 m3/year. In terms of the distribution, however, based on the analysis of water balance, there was a shortage of water supply during the dry season, particularly in July, August, September and October, that is, 7 861 736; 16 246 136; 17 800 951 and 21 384 649 m3, respectively. The simulation results of land use planning showed that the surface runoff of scenario1 was 1 073.48, scenario 2 was 1 061.25, scenario 3 was 1 056.09, and scenario 4 was 1 055.79 mm/year. The total runoff coefficient of Scenario 1, Scenario 2, Scenario 3 and Scenario 4 were 39.27, 38.72, 38.54 and 38.52 %, respectively. The surface runoff volume ratio of Scenario 1, Scenario 2, Scenario 3 and Scenario 4 were 6.08, 5.88, 5.47 and 5.47 %, respectively. Meanwhile, water storage variances of Scenario 2, Scenario 3 and Scenario 4 were 5 468 276; 7 774 304; and 7 911 617 m3/year, respectively. The simulations formulated showed that hydrologically scenario 4 was the best as indicated by the decreased in surface runoff, total runoff coefficient, and surface runoff volume ratio, and the increase in water supply during the dry season (July-October). The total economic value of water utilization in the Way Besai Watershed was Rp 108 936 635 040 per year. The highest water utilization
Keyword: curve number, landuse simulation, water demand, water economic value, water supply.