The Khmer Empire Water Management System

The Angkor civilization, or Khmer Empire, was a complex state in southeast Asia between AD 800 and 1400. It was remarkable, among other things, because of its extensive water management system stretching across over 1200 square kilometers (460 square miles), which connected the natural lake Tonle Sap to large man-made reservoirs (called baray in Khmer) through a series of canals and permanently altering the local hydrology. The network allowed Angkor to flourish for six centuries despite the difficulties of maintaining a state-level society in the face of successive dry and monsoon regions.

Water Challenges and Benefits

Sources of permanent water tapped by the Khmer canal system included lakes, rivers, groundwater, and rainwater. The monsoonal climate of southeast Asia divided the years (and still does) into wet (May-October) and dry (November-April) seasons. Rainfall varies in the region between 1180-1850 millimeters (46-73 inches) per year, mostly in the wet season. The impact of water management at Angkor changed natural catchment boundaries and eventually led to erosion and sedimentation of channels requiring considerable upkeep.

Tonle Sap is among the most productive freshwater ecosystems in the world, made so by the regular flooding from the Mekong River. Groundwater in Angkor can today be accessed at ground level during the wet season and 5 meters (16 feet) below ground level during the dry season. However, local groundwater access varies greatly across the region, with bedrock and soil characteristics at times resulting in a water table as much as 11-12 m (36-40 ft) below the ground surface.

Water Systems

Water systems were used by the Angkor civilization to cope with the vastly changing water quantities included raising their houses on mounds or stilts, building and excavating small ponds at the household level and larger ones (called trapeang) at the village level. Most trapeang were rectangular and generally aligned east/west: they were associated with and perhaps controlled by the temples. Most temples also had their own moats, which were square or rectangular and oriented in the four cardinal directions.

At the city level, large reservoirs—called baray—and linear channels, roads, and embankments were used to manage water and may have formed an intercommunication network as well. Four major baray are in Angkor today: Indratataka (Baray of Lolei), Yasodharatataka (East Baray), West Baray, and Jayatataka (North Baray). They were very shallow, between 1-2 m (3-7 ft) below ground level, and between 30-40 m (100-130 ft) wide. Baray were built by creating earthen embankments of between 1-2 meters above the ground level and fed by channels from natural rivers. The embankments were often used as roads.

Archaeologically-based geographic studies of the current and past systems at Angkor suggests that Angkor engineers created a new permanent catchment area, making three catchment areas where there once was just two. The artificial channel eventually eroded downward and became a river, thereby altering the natural hydrology of the region.

Sources

• Buckley BM, Anchukaitis KJ, Penny D, Fletcher R, Cook ER, Sano M, Nam LC, Wichienkeeo A, Minh TT, and Hong TM. 2010. Climate as a contributing factor in the demise of Angkor, Cambodia. Proceedings of the National Academy of Sciences 107(15):6748-6752.
• Day MB, Hodell DA, Brenner M, Chapman HJ, Curtis JH, Kenney WF, Kolata AL, and Peterson LC. 2012. Paleoenvironmental history of the West Baray, Angkor (Cambodia). Proceedings of the National Academy of Sciences 109(4):1046-1051. doi: 10.1073/pnas.1111282109
• Evans D, Pottier C, Fletcher R, Hensley S, Tapley I, Milne A, and Barbetti M. 2007. A new archaeological map of the world’s largest preindustrial settlement complex at Angkor, Cambodia. Proceedings of the National Academy of Sciences 104(36):14277-14282.
• Kummu M. 2009. Water management in Angkor: Human impacts on hydrology and sediment transportation. Journal of Environmental Management 90(3):1413-1421.
• Sanderson DCW, Bishop P, Stark M, Alexander S, and Penny D. 2007. Luminescence dating of canal sediments from Angkor Borei, Mekong Delta, Southern Cambodia. ​Quaternary Geochronology 2:322–329.