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Title: Impact of land use change on water yield and water quality in peninsular Malaysia
Authors: Che Ngah, Mohamad S.Y.
Issue Date: 2007
Publisher: © Mohamad Suhaily Yusri Che Ngah
Abstract: Economic development and increasing population has brought significant changes in land cover and placed stress on water quantity and water quality within tropical river catchments, including those of Malaysia. There is a need to investigate the impact of land use changes on water yield and water quality in moderate-sized (c. 1000 km2) catchments, such as the Langat and Linggi, since these provide the water resources that cater for the rapid urbanization and industrialization that characterizes Malaysia and most studies so far reported have been for very small catchments (< 25 km2, frequently <I km2). Findings from these two catchments provides information for local river managers and development planners that will assist in minimizing the negative impacts of development on water resources, while promoting sensible planning within river basins especially newly developed catchments such as the Bernam. An analysis of land-cover in the Langat, Linggi and Bernara basins indicates that there has been a significant change from forest (primary and secondary selva) to agriculture, especially tree crops (rubber, oil palm), ranging from 7-15% in the three water catchments, and an increase in the urban area that ranges from 183-394% during the period 1984-2002. Despite this, the runoff coefficient shows no significant increase during 42 years of development. The coefficient lies between 22-48%. The outcome is not straightforward and counter intuitive when comparison is made with results from other experimental catchments in the tropics, where there has been shown to be a significant increases (45-70%) in runoff when natural forests have been cleared. It is surmised that the fraction of rainfall leaving the drainage basin through the gauging station remains similar where tree crops are an important replacement for native forest and where urbanization covers less than 20% of the catchments. However, there is a significant increase in sediment yield of 19% during the development period, which is functionally related to changes in land use cover, both agricultural and urban. Biological oxygen demand (BODS), also shows a significant increase where more domestic sewage and industrial waste discharges to the river as a function of higher population and industrial growth since 1990s. Water quality considerations dictate that the catchment must be properly protected and managed to ensure sustainable development. The initial intention to establish a transfer function from a study of catchments undergoing economic development and urbanization that could then be used to predict the effects of development in undeveloped drainage basins on water relations and mitigate them has been relegated in favour of assessing catchment hydrological process-response so that the findings can be used to inform future land use management. In effect, the runoff coefficient remains similar in drainage basins of c. 1000 km2 in this environmental setting where agriculture favours tree crops and where urbanization is, as yet, modest in extent. This study suggests that up-scaling the findings of small catchment studies of forest removal is far from simple, especially in the wet tropics, where the impact of tree crops on water relations may be insufficiently distinguished from primary or secondary forests.
Description: A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/7990
Appears in Collections:PhD Theses (Geography)

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