Dependable Flow Analysis for Evaluating Raw Water Availability in the Drinking Water Supply System at Curug Weir and Walahar Weir, Karawang, Indonesia

Abstract

The Curug–Walahar weir system plays a strategic role in raw water allocation in Karawang Regency because it supports drinking water supply, irrigation, and industrial activities. This study evaluates dependable flow availability to assess the reliability of raw water supply for the drinking water supply system. Daily discharge data from 2015 to 2025 were analysed for five main flow sections using descriptive statistics, monthly discharge patterns, and Flow Duration Curve (FDC) analysis. Dependable flows were determined using Q80 and Q90 and were compared with raw water demand under two scenarios: existing water treatment plant operational capacity and projected raw water demand based on service areas up to 2044. The results show that Citarum River flow from Curug Weir (NTC-CUR) and Citarum overflow (CIT-O) have high discharge variability. In contrast, West Tarum Canal (WTC), East Tarum Canal (ETC), and North Tarum Canal (NTC-WAL) show relatively stable flow characteristics due to regulated canal operation. The existing dependable flow remains sufficient to meet the operational capacity of water treatment plants in all analysed canal sections. Future demand projections also indicate that raw water demand up to 2044 remains below the available Q80 and Q90 values. These findings suggest that the FDC-based dependable flow approach can provide an initial basis for evaluating raw water reliability in multi-use regulated canal systems, particularly for supporting water allocation planning under low-flow conditions.