Cambodia (now the Khmer Republic), in tropical, humid southeast Asia, has an area of 175,630 km and a population of about 5 million. The Mekong River, one of the world's largest rivers, flows through Cambodia. Also, the Tonle Sap (Grand Lac), a highly productive fresh-water lake, functions as a huge off-channel storage reservoir for flood flow of the Mekong River. Surfacewater discharge in streams and rivers of Cambodia is abundant during the wet season, mid-May through mid-November, when 85 percent of the precipitation falls, but is frequently deficient during the remainder of the year. Annual rainfall ranges from 1,370 mm in the central lowlands to more than 5,000 mm in the mountainous highlands. The mean annual temperature for the country is 27.5?C and the evaporation rate is high.
During 1960-63, 1,103 holes were drilled in 16 of the 18 khets (provinces), of which 795 or approximately 72 percent, were productive wells at rates ranging from 1.1 to 2,967 l/min. The productive wells ranged in depth from 2 to 209.4 m and were 23.2 m deep on the average.
Mr. Rasmussen ' studied the subsurface geology of Cambodia in considerable detail by examining drillers' logs and constructing nine geologic cross sections. The principal aquifer tapped by drilled wells in Cambodia is the Old Alluvium. In many places, however, dug wells and a few shallow drilled wells obtain water from the Young Alluvium. Sandstone of the Indosinias Formation yields moderate to small quantities of water to wells in a number of places. Also, wells tapping water-bearing basalt have a small to moderate yield. The quality of water is recorded in only a few analyses. The dissolved solids concentrations appear to be generally low so that the water is usable for most purposes without treatment. Some well waters, however, are high in iron and would have to be aerated and filtered before use. In this report, well records are tabulated, and the geology and hydrology is discussed by khets. The bulk of the available information is on the central lowlands and contiguous low plateaus, as the mountainous areas on the west and the high plateaus on the east are relatively unexplored with respect to their ground-water availability.
No persistent artesian aquifer has been identified nor have any large potential ground-water sources been found .although much of the country yet remains to be explored by test drilling. Well irrigation for garden produce is feasible on a modest scale in many localities throughout Cambodia. It does not seem likely, however, that large-scale irrigation from wells will come about in the future. Ground water may be regarded as a widely available supplemental source to surface water for domestic, small-scale industrial, and irrigation use.