Geological Society of Malaysia, Bulletin 46, May 2003; pp. 431-437
1Geophysics Group, School of Physics, University of Science Malaysia, 11800 USM Penang
2Department of Geology, University of Malaya, 50603 Kuala Lumpur
Abstract: The Putrajaya Lake and Wetlands complex is the main and the biggest component of Putrajaya, the new Malaysian Government Administrative Centre. The lake, which covers an area of about 7.0 km2, was artificially created to become the aesthetic centre of Putrajaya. Maintaining the water quality of the lake is the most important aim of the lake management programme. To maintain the good quality of water and aquatic life within the lake, the Putrajaya Corporation (Perbadanan Putrajaya) has created a monitoring and research unit, comprising the KLCC-UH (KLCC-Urusharta Sdn. Bhd., a private company) and a research team, to continuously monitor, investigate and report on all aspects of the Lake and Wetlands. This paper describes and discusses the results of the hydrological and sediment monitoring program for the months of October 2001 until May 2002 for Lake IA and the Wetlands, focusing on the hydrological and sediment-transport systems within the wetlands.
Data on rainfall, water-discharge, TSS (Total Suspended Solid) and TSS-discharge for the months of October 2001 to May 2002 were analysed. The rainfall pattern shows two prominent modes, one around the month of November 2001 and another around the months of April-May 2002. The water discharge trends measured at all the wetland arms show prominent peaks at around November 2001 and April-May 2002 and closely correspond to the rainfall pattern. The results clearly indicate that water-discharge at the northern Putrajaya Wetlands is very much governed by rainfall.
The TSS concentration trends recorded at the different wetland arms show peaks which corresponds to the water-discharge peaks for the period October 2001 to May 2002. Erosion and transportation of earth’s surface material becomes more rapid during intensive events such as flooding and storms. High rainfall coupled with the availability of fresh sediment sources in upstream catchment areas, due to land clearing results in greater erosion and sediment yield, and sediment discharge in the wetland cells.
The TSS-concentration graphs also display other peaks during periods of low rainfall between November 2001 to April 2002, and these peaks indicate that there are other factors involved in determining the volume of TSS entering the wetlands. The TSS-discharge trends at the different wetlands closely resemble the water-discharge trends (and not the TSS-concentration trends). Water is the main medium that transports the TSS, downstream, along the wetlands. Thus, although the concentration of TSS may be high during months where rainfall is low, only a small volume is transported downstream, along the wetland cells, due to the low water-discharge volume.