This paper aims to develop and implement a set of criteria to locate reservoir sites on the Langkawi Island using remotely sensed data and GIS.

2. The study area
Langkawi Island lies off the northwest coast of Peninsular Malaysia and located approximately at latitude 6o20'N and longitude 99o40'E (Fig.1). Its annual average rainfall is 2430mm (Shaaban and Sahat, 1995; Wan Yusof and Baban, 1999). Most streams have small catchment areas and they tend to flow downstream rapidly from the mountain to sea. As such their flow tend to cease during periods of dry weather (Syed, 1992).

3. Methodology
Factors influencing reservoir site selection includes topography, hydrology, geology, soil, land use/land cover, road network as well as socio-economic and environmental factors (Gismala et.al., 1996; Murphy, 1977). Based on these factors and the development guidelines by Langkawi District Council (1992), criteria for locating reservoir in the Island was developed (Table 1). The reservoir sites should not be in the vicinity of densely populated areas, must be located on land providing a strong foundation and there should not be any development in the forest reserve areas, hence constraint criteria 1, 2 and 3. Constraint criteria include numbers 4, 5 and 6 will ensure the necessary degree of suitability within the classified areas such as avoiding high grade agricultural land, having the pre-requisite altitude and slope. Constraint 7 was included to account for the projected demand for water supply in the Island. Total water demand was projected to be 70 megalitre/day (Mld) in 2010 (Syed, 1992). As a general guideline, a common dam height is between 15 and 30 m (Morris and Fan, 1997).

Criteria	Consideration
The dam and reservoir site must:
(1) not be located in or within settlement areas	Safety
(2) be on granite and/or metamorphic rock	Safety
(3) avoid forest reserved areas	Resources/Environment
(4) avoid high grade agricultural land value areas	Resources/Environment
(5) be at an altitute of between 25-90 m	Hydraulic/ Economic
(6) be on a gentle slope of 0o-11o	Environmental/Safety
(7) have a sufficient surface area to provide the necessary volume	Consumption/Economic

If two reservoirs were developed, the water demand would each reduce to 35 Mld in 2010. This would require a water storage capacity of 16,425 x 103 m3 yr-1 with a maximum surface area of 85.2 ha for dam height of 15 m and a minimum surface area of 25.5 ha for dam heights 50 m.