In late January, I stood at the edge of Angkor Wat’s north baray, looking out over this vast reservoir dug during Angkor’s medieval heyday. In the 15th century, the once powerful kingdom collapsed suddenly and somewhat mysteriously. Two conversations led me to this place — one with a Cambodian hydrologist, and another with an Australian archaeologist. Both talked about water, the lifeblood of Cambodia, then and now, and the singular source of prosperity and vulnerability.
It was quiet by the water, which covers about 3.5 square kilometers. Most tourists had stopped at the Preah Khan temple complex just to the west, a labyrinth of stone towers, pavilions, shrines and bas-relief carvings, commissioned in the late 12th century by King Jayavaraman VII. Its sanctuaries are dedicated to the Hindu gods that dominated Angkor’s early years, and to the Buddhism that later prevailed.
The baray is much less photogenic. Tangles of water hyacinth float in the shallows. Further out, dead trees and shrubs pierce the surface, vestiges of the centuries when the baray was dry following Angkor’s sudden collapse. Between the skeletal trees, a wide, watery path reflects blue sky and high clouds, marking the now-submerged road to the baray’s island temple, Neak Pean. Water returned to the baray in 2008, after hydrologists repaired the canals that feed the reservoir. This wasn’t just historical restoration; it was a rescue mission. Angkor needed to be saved from its own success.
In 1992, UNESCO listed the 400 square kilometers of crumbling temples as endangered and sparked an international preservation effort. By 2004, the restoration had advanced sufficiently for UNESCO to remove Angkor from the endangered list. At the same time, however, Angkor was being undermined by the growing crush of visitors. Besides the obvious wear and tear from millions of tourists clambering over the ruins, a more insidious threat was the booming city of Siem Reap, about five kilometers away, near Lake Tonle Sap. Siem Reap’s residents and hotels sucked more and more water from the underground water table that extended below Angkor and was unable to recharge naturally from rainfall, because of the deforestation in upland areas. As the sand below the heavy temples dried out, it could no longer support the weight. Walls began to buckle and collapse.
That’s when hydrologist Hang Peou, deputy director of APSARA (the Cambodian authority in charge of Angkor), began looking for a solution from Angkor’s medieval past, when a sprawling city surrounded the temples. Only the immortal gods had stone edifices. Everything else was made of thatch or wood. Even the palaces were destined to vanish with time. The best archaeological evidence of Angkor the city is a vast network of canals, dykes and moats, many of which had long since gone dry. The waterworks had multiple purposes — they controlled the floods, irrigated the rice and surrounded the temples with water to represent Mount Meru, the abode of the gods and the center of the universe in Hindu mythology. One of the first scholars to recognize their importance was the French archaeologist Bernard-Philippe Groslier, who wrote a paper in 1979 calling medieval Angkor a “hydraulic city.”
“They faced the same problems that we have today,” Peou had explained earlier that morning when we met in front of Angkor Wat. Too much water in the rainy season, and not enough in the dry season. “If we can just restore it, we can manage it.” But how? The waterworks of medieval Angkor were built piece-by-piece over several centuries. Since the kingdom’s fall, much of it had been covered by roads, settlements and dense vegetation.
“Groslier called Angkor a hydraulic city, but he didn’t know how it functioned,” Peou told me. To find out, Peou used a combination of modern hydrological computer models along with clues from medieval stone inscriptions and the old place names remembered by local Khmer people who live in nearby villages. In eight years, the APSARA department of water management has re-flooded the north baray and the even larger west baray, and reconnected these water storage systems with moats, stabilizing the temple foundations.
They have also incorporated irrigation diversions for local agriculture and modern spillway gates to control the flooding during the monsoons. They hope to reflood two other major barays soon. For now, Peou and his staff keep tabs on the system by driving out to every baray and moat and having a look. It’s labor intensive, and Peou is hatching a plan to incorporate water level sensors that would feed real-time data to a headquarters where technicians could open and close gates remotely.
No such luxury existed in medieval Angkor, of course. And a growing consensus among archaeologists is that the same waterworks system that fueled Angkor’s rise may have ultimately grown too big, complicated and unwieldy, contributing to the kingdom’s collapse. "Contributing" is a key word, because late medieval Angkor certainly had other problems — increasingly powerful and aggressive neighbors kept invading it, for instance. Meanwhile, the growing importance of maritime trade meant that power was shifting toward the coasts.
But a breakdown Angkor’s flood-control and irrigation system would have made the place unlivable, according to Roland Fletcher, an archaeologist at the University of Sydney, who has coauthored several papers on this theory since 2008. In one paper, from 2010, Fletcher and colleagues reported evidence from tree-ring data of substantial climate shifts — severe droughts interspersed with especially intense monsoons — beginning in the late 14th century (the transition from the medieval warm period to the global cold snap known as the “little ice age”).
“It was the inertia, the huge scale and the complexity [of the system] that was the problem,” Fletcher told me when we spoke by Skype. It wasn’t flexible enough to accommodate the newly severe floods and droughts. The system broke down and couldn’t be repaired. “The moral of the tale is: Don’t put your eggs in one big complicated basket,” Fletcher told me.
When I asked Fletcher if he drew analogies between the fate of medieval Angkor and the ongoing deforestation, expanded irrigation and hydropower damming of Lower Mekong Basin with looming climate change, he demurred. His expertise is decoding the past, he told me, not passing judgment on the present.
“The point I’ve made,” said Fletcher, “is if you look at greater Angkor, you have a giant, low density city, which clears the natural vegetation and replaces it with economic vegetation such as rice, and builds itself into a mega infrastructure on which it is critically dependent, and then the climate changes. Does this sound topical?”