DEVELOPMENT FLOW DURATON CURVE FOR CRITICALITY ASSESMENT OF RIVER BASIN APPLIED AT THE UPPER CITARUM RIVER BASIN, INDONESIA

Abstract

A river basin is a landscape unit in which a hydrologic cycle completely occurs in every respect. River basins, initially healthy and natural, are slipping into critical conditions, affected by urbanization processes. Hydrologic imbalance happens due to land-use change resulting in increased runoff and reduced soil infiltration capability. The change of a river basin from a fine healthy hydrologic condition into a critical state is shown by flow duration curve and its least square line. Having been applied at the Upper Citarum river basin using ArcSWAT hydrologic model and SWAT-CUP calibration program, the curves could map the
health range of the river basin showing wheather the river basin was heading towards a critical condition.Based on modeling of FDC on natural and fully utilized condition, the criticality feature is the increase in high flow and decrease in low flow. The upper Citarum river basin was in criticality process which shown by high flow increases and low flow decreases over the period 1981-2010. Using model of FDC’s gradient, the criticality value of the period 1981-1986 was 3.15 and it increased to 3.35 in the period of 2005-2010. The increase is correlated with land use change in increasing settlements, dry crops, barrenland, and forest decline.