Abstract

Lui River and Langat-Dengkil River sub-basin are one of the large portions of Langat River catchment, known as the prime and important water source for Kuala Lumpur, Petaling Jaya, Shah Alam, Klang as well as domestic and industries usage in the Langat River basin itself. Unfortunately, the land-use change has greatly impacted the base-flow regimes particularly for the upstream area of Lui River sub-basin and downstream area of Langat-Dengkil River sub-basin.  Base-flow separation method based on United Kingdom Institute of Hydrology (UKIH) smoothed minima method was adopted to estimate base-flow from daily stream-flow data. An index namely, base-flow index (BFI) is used to give the ratio of volume of base-flow (V_B) to the total stream-flow (V_A). The graph of yearly BFI time series has exhibited the unchanged or constant trends in Lui River sub-basin ranging from 0.3625 to 0.7184. In fact, downward trend in Langat-Dengkil River Sub-basin has vigorous fluctuation ranging from 0.2465 to 0.7356.The comparison of BFI in dry and wet period for both Lui and Langat-Dengkil River sub-basin was carried out for certain years (6 years for both cases for certain reasons) to identify the quantity of river’s runoff derived from the stored sources particularly in dry period to sustain continuous flowing of water in the river. In order to analysis the low-flow regimes, technique 7-day 1-years (7Q1) was used for both Lui and Langat-Dengkil Sub-basin.  The 7Q1 help to provide information of availability of water supply as well as robustness of the system particularly in drought period for both Sub-basins over the time.

Key words: Lui River, Langat-Dengkil River, base-flow separation, United Kingdom Institute of Hydrology, base-flow index, low-flow.

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