HYDROLOGY MADE SEXY

Angkor is an amazing place. You can not fail to be impressed even stunned by the grandeur, detail and scale of the monuments. The true wonder of the Angkorian Empire and what it had achieved had only started to dawn on me in the last few years. It was when the findings of the Lidar survey surfaced that I grasped the extent of what was one of the world’s greatest civilisations.

Lidar in layman’s terms emits an electromagnetic pulse – a lazer, that is strapped to a helicopter and fired as it passes over the ground to be surveyed. The reflected light is fed through software that strips away the vegetation to reveal the topography and previously unidentifiable structures.

The results are phenomenal! Phnom Kulen had a city on top. Angkor Thom was laid out in a grid of roads and canals framing wooden houses and their trapaeng or pools. There were thousands of temples not hundreds, and it was all made possible by the management of water in a climate where at the best of times 6 months of rain is followed by 6 months of drought.

I also began to realise that many of our cycle routes, hiking trails and even kayaking adventures followed these ancient waterways. I’d heard Roland Fletcher give fascinating talks at Amansara and on the banks of the West Baray. It wasn’t until Damian Evans (also from Sydney University) spoke to the guides I was working with that I knew he could tell us what we needed to put together the pieces of Angkor.

The Water Connection

Boeung Ta Neue, one of our kayaking destinations, was an Angkorian reservoir. The reservoir caught the rain run off from the Kulen Hills to the North and in turn fed the East Baray, a giant rectangular water storage 2km wide and 7km long.

Kayaking on Boeung Ta Neue Angkorian Reservoir

Opposite the North East corner of the baray is the 7 arched Spean Tor Bridge. Clearly visible by kayak from the water, we managed to reach it through the bush from the red earth road where Damian had parked.

We searched on the Baray side for an exit but with none to be seen, we couldn’t work if water flowed directly into the Baray or through Kral Romeas , a sluice built into the banks of the East Wall.

Spean Tor Bridge

Cycling and hiking through Phum Samre, the village that lines the walls I’d noticed large laterite blocks and dismissed them as scattered ruins. Closer inspection revealed 1 large thick wall and 30 metres away another running parallel. These formed the sides of the sluice, the raised ground in front of us was a laterite weir. Kral Romeas acted over time as an inlet and outlet to the reservoir and may have been connected by another laterite wall running parallel with the East Bank, to the reservoir via Spean Tor.

An outlet has also been discovered 7km away in the West Bank, which provided water for the wooden houses between Angkor Thom and The Baray, and fed into the Ta Prohm moat. The Baray seems to have been a huge body of water to supply what appeared as a compact area of habitation but it would also have been used for irrigation.

Damian put this into context by working out that the 50 million litre3 in the West Baray of similar size to the East Baray, could provide irrigation for 5000 ha of rice, perhaps 10,000 tonnes for each crop. To feed a population of hundreds of thousands of priests, aristocracy and merchants who lived in and around the ancient temple cities.

The West Baray (full)

It was also unlikely that the 3 great water reserves of the West, East and North Baray were in simultaneous use but acted as a stabilising backup for the climactic peak’s and troughs in rainfall.

The scale of these man made hydraulics are unparalleled in human history and mind-boggling. The 3 spatial dimensions have to be combined with a 4th chronological dimension as the kings and climate changed over time. History seems to have been determined by the weather as the peaks in the empire, 1st during the reign of Suryavarman II in the 12th century then under Jayavarman VII in the 13th century coincided with peaks in rainfall as we saw from the historical records on Damian’s computer screen.

The ultimate decline of Angkor was also linked to periods of extreme drought followed by flood years, which washed away the channels needed to supply water during the dry season. This is most clearly seen at Spean Thmor between Ta Keo and Angkor Thom where the old bridge lies high up the banks of the river which now runs meters below.

Prasat (temple) Tor lies between Beoung Ta Neue and the East Baray and at the corner of a mysterious 10 x 10 grid of a 100 mounds.

Similar grids have been found beside the River of a Thousand Linga’s at Kbal Spean and Sambor Prei Kup near Kampong Thom, both associated with major water systems.

Prasat Tor and it’s 3 laterite towers

To date excavation has not revealed any artifacts associated with or identified the purpose of these mounds. Walking through the site with Damian we spotted fragments of curved roof tiles in a papaya plantation that in an unintended act of vandalism, has been planted right over the mounds, which may help in solving the mystery.

Most of what is known about Prasat Tor comes from a 4 sided stele discovered by the French in the 1930’s and now stored in The Angkor Centre for Conservation. The Sanskrit engravings were translated and available on line, which Damian translated for us in his office that morning. The stele had been installed, and perhaps part of the temple built by a Brahmin priest during the 13th century referring to the Great King Jayavarman VII. The inscription mentions the Ganges River in association with water, which may have had something to do with the Kral Romeas sluice and was the same as an inscription found at Phnom Dai a temple to the North and also the site of another grid of mounds.

Prasat Tor itself appears to predate the stele and judging by the motifs on the intact lintel, Damian found out that they bore similarities with those in Angkor Wat built during the reign of Suryavarman II in the first half of the 12th century.

Randomly cast on the ground were the now eroded but once richly carved blocks that adorned the structure including a stone crown that sat atop the central tower. Interestingly it had a hole in the middle, where a bronze finial in the form of a trident could have been positioned. Possibly removed at certain auspicious times of the year to bathe Shiva in sunlight 15 meters below.

Now amongst brilliant green paddy fields in November, on the other side of Beoung Ta Neue is the 10th century Leak Neang Temple. Built at the same time as the spectacular brick temple of Preah Rup. A stele has recently been removed from that site and is also now in the Angkor Conservation but has yet to be translated.

Leak Neang with its single brick tower

The bricks themselves are another mystery as no kiln has ever been found. A theory speculates that the bricks were fired close to the temples then used in it’s construction. The apparent black scorching seen on the walls seemed to support this idea.

Not only was this masterly management of water used to supply The Angkorians and irrigate their crops, it also conveyed an enormous amount of stone used to build the city. Laterite is an iron rich clay that is soft and easy to dress into blocks when it comes out of the ground. On exposure to the sun it becomes very hard but relatively light making it ideal for the foundations as its pock-marked surface is not easily carved. The laterite quarries lay in the hills to the West. Dams collected water from streams, which was released into the Great North Channel that carried the stone blocks South to the North Baray.

At the Eastern end of the Kulen escarpment were quarries that supplied sandstone, which was carved into the marvelous facades of the temples.

A channel ran from Beng Melea past the Temples of Banteay Ampil and Chau Srey Vibol to Prasat Batchum inside Angkor.   A path still connects these sites and makes for a great cycle ride with temple stops for sustenance on route (perhaps a champagne lunch inside The Tamarind Temple – Banteay Ampil).

View from the walls at the S.E corner of Angkor Thom

We were beginning to get a handle on the Eastern end of the water connection, now it was time to explore the Western end. The Siem Reap River flows South from the Kulen Hills to the the city and then onto the Tonle Sap Great Lake but during Angkor it was diverted into the North East corner of the Angkor Thom Moat. History is being repeated as subsequent to the floods of 2011 the channels have been reopened and another dug in parallel on the North side of the moat as the river is diverted into the West Baray with the aim of stopping the floods in Siem Reap. The fact that now the town of Puok to the West floods instead is not part of the discussion – tourists don’t go there.

Boeung Thom (big lake)

Angkor Thom was Jayavarman VII’s and his 2 wives city. The largest of all the Angkorian Cities its wall’s 3km long enclose 900 hectares or 9 km2, which is now mainly forest but once housed a thriving metropolis of wooden houses and their trapeang (pools), surrounded by a grid of canals and roads as the Lidar survey revealed. The data was detailed enough to show the individual houses, which can be extrapolated to give a guesstimated population of 70,000 based on an assumed family size. This would need a lot of water but during the rainy season if there was an excess it flowed out of the Boeung Thom reservoir in the South West of the city and through Runta Dev to the moat and thence on to a canal flowing South. Incredibly the city is a meter and a half higher in the North East compared to Runta Dev in the South West so water flowing in from the Siem Reap River drained through the city into Beoung Thom, which may have acted as a natural sewage disposal plant then out via Runta Dev into the moat. Another amazing example of how sophisticated the Angkorian engineers were.

Our cycle route runs along the 8m high walls of Angkor Thom to Prasat Chrung or corner temple. A great late afternoon spot for watching the sun set over the moat, paddy fields and palm trees beyond. We didn’t realise the engineering marvel of Runta Dev that lay 8m below us until Damian lead us down the inner banks to a stream that on closer inspection disappeared into a laterite tunnel under the walls and out to the glinting light of the moat 30m away.

Runta Dev

The West Baray 500 meters to the West is one more mystery. How was this vast body of water replenished and released during times of flood? The current outlet of the Angkor Thom moat is a canal running parallel with the road through the West Gate that flows into the Baray. Dug by the French in the 1930’s it may have destroyed any trace of what was there before. It is possible it was a replacement otherwise how did 50 million litres of water get into The Baray.

West Baray (empty)

What had we learnt that morning?

We understood that water running off the Kulen Hills to the North fed streams which flowed into the reservoir of Boeung Ta Neue in turn feeding the East Baray, which was a water supply for the population East of Angkor Thom and Ta Prohm itself.

Damian confirmed that our cycling path to Chau Srei Vibol and on to Banteay Ampil, lay along the route a canal had taken bringing sandstone from the quarries at the Eastern end of the Kulen escarpment via Beng Melea to Angkor.

He explained how the laterite used to build the foundations of the J VII temples was carried by water released into the Great North canal which flowed to the North Baray and Preah Khan.

And the Western hydrological connection was made by the Siem Reap River flowing into the Angkor Thom moat and maybe on into the West Baray.

And much else besides!

With great thanks to Damian Evans for a really fascinating morning and apologies for any misinterpretations.

Indochine Exploration with Smiling Albino Cambodia is pleased to take our guests on an introductory investigation of the main temples along the water courses described or an adventure to see at first hand how the water connection was made.