Riparian buffers in tropical rivers

Riparian buffers in tropical rivers

11.02.2010 - Posted by Dom Blackham
Sarawak is the largest state in Malaysia, located on the island of Borneo. It still has vast tracts of intact rainforest, some of which are home to populations of orangutans, now considered to be a threatened species. 

Large-scale deforestation has occurred across Malaysia, particularly in the period since independence from Britain in 1963. The Food and Agriculture Organisation of the UN estimates that Malaysia as a whole lost approximately 140,000 hectares of forest between 2000 and 2005. The well documented environmental consequences of deforestation include increased erosion, carbon release and water quality impacts, but the Malaysian government is trying to balance these impacts with the social imperative to increase the quality of life for its large rural population who have, to date, been largely bypassed by the benefits of economic development.

We have been working with the Natural Resources and Enviroment Board of Sarawak to develop a tool to define the width of forest or grass strips alongside rivers that must remain intact to protect the instream ecosystem from sediment loads and water quality impacts. These areas, known as riparian buffers, are critical for river health but the lack of scientific infomation about their effectiveness in Sarawak hampers the ability of the government to enforce the adoption of riparian buffer widths in association with land development activities.

In partnership with Malaysian consultants Chemsains we developed a riparian buffer tool that determines the minimum riparian buffer width required at a site to reduce the impact of sediment transport from upslope areas. To address the significant knowledge gaps we carried out a series of controlled field experiments using portable flumes that allowed us to control inflow rates, sediment concentrations, hillslope and vegetation type. The results from the experiments were combined with a simple model of soil erosion rates to form the riparian buffer tool, which can be applied at any site in Sarawak to determine the minimum required buffer width.

Some images of the field experiments are shown below.

Looking upstream at the the Batang Ai flume: v-notch weir at the downstream end for measuring flows.

Looking downstream at the Batang Ai flume. Note the mature grassy vegetation inside the flume prior to the experiment starting

Close up of grassy vegetation in Batang Undup flume.

For more information on the riparian buffers project please email Michael Bain at [email protected].