Soil erosion and its impacts on water treatment in the northeastern provinces of Thailand

Abstract

The economy of Northeast Thailand is mainly based on agriculture. The transformation of forestlands to agricultural areas and the encroachment of riverbanks within the Phong watershed have caused severe soil erosion. Strong storms in rainy season exacerbate the problem of soil erosion. Difficulty in getting water drives people in the upstream region to live on riverbanks. Soil erosion affects water utility by increasing the turbidity in the Phong River and also by decreasing the water storage capacity of small reservoirs for the upstream residents, as well as that of the Ubolratana Dam. The rate of siltation in the Ubolratana Dam was estimated to be 1.5 million tons/year during 1965–1990. The main source of water supply is surface water in the Phong watershed, and fluctuating turbidity makes water treatment difficult. The maximum turbidity in the upstream Phong River exceeds 5000 NTU, whereas it is reduced to be about 300 NTU at the intake point of Khon Kaen Municipal Water Treatment Plant because the Ubolratana Dam works as a huge clarifier. Khon Kaen Municipal Waterworks has a daily water supply of 72,960 m 3/day. The average amounts of alum used in the wet (May–October) and dry (November–April) periods are 42.33 g/m 3 and 28.46 g/m 3, respectively. The average costs of the amounts of alum used are 0.213 and 0.143 Bahts/m 3 during the wet and dry periods, respectively. Fluctuation of turbidity in raw water makes it difficult to adjust alum dose, resulting in treated water quality unstable, and handling of sludge disposal difficult.