National Geographic : 2009 Jul
• canals and dikes that relied on subtle di erences in the land s natural inclination to divert water from the Puok, Roluos, and Siem Reap Rivers to the barays. During the summer monsoon months, over ow channels bled o excess wa- ter. A er the rains petered out in October or November, irrigation channels dispensed stored water. e barays may also have helped replen- ish soil moisture by allowing water to soak into the earth. In surrounding elds surface evapo- ration would have drawn up the groundwater to supply crops. "It was an incredibly clever sys- tem," says Fletcher. at clever water system may have made the di erence between mediocrity and greatness. Much of the kingdom s rice was grown in em- banked elds that would otherwise have relied on monsoon rains or the seasonal ebb and ow of water on the Tonle Sap oodplain. Irrigation would have boosted harvests. e system could also have provided survival rations during a poor monsoon season, says Fletcher. And the ability to divert and impound water would have a orded a measure of protection from oods. When other kingdoms in Southeast Asia were struggling to cope with too little or too much water, he says, Angkor s waterworks would have been "a profoundly valuable strategic asset." Thus Fletcher was baffled when his team unearthed one of the more extraordinary pieces of Angkorian workmanship---a vast structure in the waterworks---and found that it had been demolished, apparently by Angkor s own engineers. IT'S ALMOST NOON on a June day about ten miles north of Angkor Wat, and even at the bottom of a muddy, 14-foot-long trench, there s no re- lief from the erce sun. Fletcher takes o a dark blue baseball cap and wipes his brow. It looks as if the self-possessed researcher is going to launch into a precise explanation of the gray- ish red stone blocks his team, along with Chhay Rachna of APSARA, has unearthed. Instead, he sighs and says, " is is simply fantastic!" The stone blocks fitting snugly together were hewed from laterite, a spongy, iron-laden soil that hardens when exposed to air. When Fletcher and Pottier rst found a section of the structure a few years ago, they thought it was the remains of a small sluice gate. "It s turned into a monster," he says. The blocks are the remnants of a spillway across a sloping dam that may have extended as long as a football eld. Around the end of the ninth century, with Angkor blossoming, engineers ex- cavated a long canal that altered the course of the Siem Reap River, redirecting it southward to the newly constructed East Baray, a reser- voir nearly as big as the later West Baray. e dam, positioned in the river, diverted water to feed the canal. But part of the massive structure may also have functioned as a spillway during monsoon surges, when water would have over- topped the low structure and owed down the former river channel. e ruins of the spillway are a vital clue to an epic struggle that unfolded as generations of Khmer engineers coped with a water system that grew ever more complex and unruly. " ey probably spent vast portions of their lives xing it," says Fletcher. Some of the dam s blocks lie in a jumble; huge sections of masonry are missing. " e most logical explanation is that the dam failed," Fletcher says. e river may have chewed into the dam, gradually weakening it. Perhaps it was washed away by an unusually heavy ood, the kind that comes along every century or even every 500 years. e Khmer then ripped apart much of the remaining stonework, salvaging the blocks for other purposes. Another clue that the water system was fail- ing comes from a pond at the West Mebon, an island temple in the middle of the West Baray. Pollen grains preserved in the muck show that lotuses and other aquatic plants ourished in the baray until the early 13th century. Then new kinds of pollen appear, from species such as ferns that prefer marsh or dry land. Right at Angkor s zenith, one of its reservoirs ap- parently went dry for a time. "Something was BAS RELIEFS DEPICT EVERYDAY SCENES MEN HUNCHED OVER A BOARD GAME, A WOMAN GIVING BIRTH. THEY ALSO REVEAL TROUBLE IN PARADISE. ■ Society Grant This project was funded in part by your National Geographic Society membership.