WATER BALANCE ANALYSIS USING WATER EVALUATION AND PLANNING (WEAP) MODEL (STUDY CASE: CIMANUK WATERSHED, CIMANUKCISANGGARUNG WATERSHEDS, WEST JAVA PROVINCE)

• Main Author: Ardya Prameswari, Aurel
• Format: Theses
• Language: Indonesia
• Subjects: Teknik saniter dan perkotaan; teknik perlindungan lingkungan
• Online Access: https://digilib.itb.ac.id/gdl/view/86622
• Institution: Institut Teknologi Bandung

The Cimanuk Watershed is utilized for raw water supply, industrial activities, and irrigation. The increasing population within the Cimanuk Watershed and land-use changes over time are expected to raise water demand. Therefore, it is essential to conduct a water balance analysis to ensure equilibrium between the water availability and the water demand in the Cimanuk Watershed. One approach to perform this analysis is through simulations using the Water Evaluation and Planning (WEAP) software. This study aims to identify the water availability in the Cimanuk Watershed for the year 2023, assess its water demand in 2023, simulate the water balance for 2023, and project water management scenarios and water demand fulfillment (% coverage) for the years 2033 and 2043. The methodology of this research includes the collection of secondary data, rainfall data processing, calculation of water availability and water demand, schematic modeling in WEAP, scenario development for water availability and demand in 2033 and 2043, simulations of the actual water balance for 2023 and projected scenarios for 2033 and 2043, followed by an analysis of the water balance and water demand fulfillment for both the actual and projected scenarios. Water availability scenarios are based on flow conditions: Q10% (very wet conditions), Q20% (wet conditions), Q50% (normal conditions), Q80% (dry conditions), and Q90% (very dry conditions). The water demand scenarios for PDAM (local water company) are projected based on population growth, while industrial and irrigation water needs are projected based on land use plans. Additionally, for future projections, water demand for shallot farmers group or KTBM is assumed to decrease. The pattern of discharge during the rainy and wet seasons in the Cimanuk Watershed follows the same pattern as the rainfall, which peaks from November to May, corresponding to a monsoonal climate. WEAP validation was conducted by comparing the simulated discharge to observed discharge data in 2023 at the Cipasang Station, yielding a correlation coefficient of 0.96, a coefficient of determination of 0.92, an NSE of 0.84, and an NRMSE of 18%, indicating the model's high accuracy in simulating river discharge. In 2023, water availability in the upper Cimanuk Watershed ranged from 13.34 m³/s to 84.11 m³/s, while in the downstream of Cimanuk Watershed it ranged from 16.46 m³/s to 192.09 m³/s. The total water demand in 2023 for the domestic, irrigation, industrial, and KTBM sectors in the Cimanuk Watershed was, respectively, 1.81 m³/s, 13.62– 103.39 m³/s, 0.22 m³/s, and 1.09 m³/s, measured on a bi-monthly basis. The 2023 water balance for the downstream Cimanuk Watershed indicated a surplus. However, 15 out of 133 demand sites experienced water deficits. In 2023, the irrigation and industrial sectors achieved an average water demand fulfillment of 98.45% and 98.71%, respectively, while PDAM and KTBM sectors reached 100%. The most extreme water deficit in 2023 occurred in the Cigasong Irrigation Area, which draws water from the Cideres River (a tributary). For the projected water demand scenarios in 2033 and 2043, there will be the addition of 18 industrial areas and 1 PDAM, increasing the total number of demand sites to 152. The water demand fulfillment for PDAM, irrigation, industry, and KTBM sectors in 2033 and 2043 is projected to exceed 95%, 80%, 23%, and 100%, respectively. The largest unmet demand or water deficit in 2033 and 2043 is projected to occur in the irrigation sector, with total deficits exceeding 100 m³/s. The most extreme deficits for 2033 and 2043 are expected to occur in the Cigasong, Kiararambay, and Tirtanegara Irrigation Areas. This is primarily due to insufficient water availability from the Cideres River, and WEAP's prioritization of PDAM water needs, which are located downstream of these irrigation areas.