Various engineers believe the East Coast Conservancy Dam is not only over-topping but has been seeping also. Managing Director of CEMCO Ltd Raymond Latchmansingh believes the main cause of the flooding could be attributed to "over 50 inches of rainfall." But the former chief hydraulics officer added that the "dam has a seepage problem and is also over topping."

The dam was built on the old plantation system whereby planters used to empolder their property to prevent water from the back lands getting onto their property, as well as for stopping seawater.
In a report prepared by Latchmansingh it was noted: "the East Demerara Water Conservancy was developed in 1880 to channel a number of water sources, for a more efficient water storage and distribution system from the Lama and Maduni River catchments. The principal users of the water are the sugar-cane plantations, rice and cash crop farmers on the East Coast and East Bank Demerara and the City of Georgetown.

"The conservancy was formed between the Mahaica and Demerara rivers by damming the flow of the Lama and Maduni rivers approximately 28 and 31 miles respectively up the Mahaica River from the coast.
"The dam, which holds a volume of more than 100 square miles of water, was built by manual labour using soil borrowed from the conservancy side of the dam. The soils of the area are predominantly deep organic peats (pegasse) overlying soft clays and silty clays. The dam has been compacted and consolidated over the years, but still remains prone to seepage, piping and slippage. The dam levels tend to settle gradually because of the high organic content.

"Maintenance of the dam therefore needs to be continuous. Loss of the water from the conservancy has also been an increasingly major problem over the past 20 years. The main areas of weakness are the defective intakes, which are generally very old and the adjacent dam areas.
"In previous assessments the dam was known as the 'paper dam' because of the pegasse material that is present in many sections, including the foundation. It has been the subject of several investigations into the feasibility of raising or realigning the dam.

"In 1950, proposals were made for the control of the Mahaica River, which integrated all aspects of water control in the conservancy. The proposal was based on the fact that the East Demerara Water Conservancy suffers from a water shortage in dry weather while the Mahaica river has surplus fresh water going to waste, hence the proposed solution was to use this surplus.

"Within the recent years erratic weather patterns combined with declining standards of maintenance has led to the severe weakening of the dam. During the 1997-1998 El Nino events the dam was severely weakened and conditions for widespread slippage failure were evident. The unstable conditions were further compounded by the reluctance since the early 1990s to operate the sluices at Maduni during periods of heavy rainfall in consideration of the risk of flooding residents along the Mahaica River banks.
"The result has been the conservancy is regularly operated above its design Full Supply Level (FSL) of 57.5 Georgetown Datum (GD). This mode of operation has been associated with overtopping and a number of minor breaches over the decade and has undoubtedly contributed to weakening the dam. The major breaches of 2000, which occurred near the Lusignan and Hope intake structures were a direct result of over topping following extended periods of water shortage above the FSL."

The crown dams were built to protect the plantations from the seepage of water from the conservancy dam. Latchmansingh said that right now farmlands extend right up to the crown dams, but in other cases, there is no crown dam as this has been taken up by farmers.  

In terms of what should be done right now Latchmansingh said, "there needs to be a quick calculation of how much water is there to be drained with or without continued rainfall." He said it was necessary to take another look at the drainage systems including the sluice capacities that may have to be re-engineered to handle a larger volume of water.

With regard to the city he said: "We are looking at a system that was catering for two and a half square miles that is now catering for 16 1/2 square miles with no further drainage except in areas such as Meadowbrook and the Dowding Canal."

Latchmansingh proposed the re-engineering of the whole area as well as looking at storage capacity and maintenance.

In response to the question raised about aquifers being a part of the flood problem Latchmansingh said this was not so. But he stressed that it was necessary to "monitor aquifers because they develop subsidence." This subsidence or settling, he noted, can lead to eventual flooding with water coming in from the rivers and the sea. Aquifers lie some 900-1200 feet below the surface and are currently not being monitored. They should be monitored by Guyana Water Inc using an instrument called the piezometer, which measures pressure or compressibility.

Another engineer attached to the University of Guyana said the conservancy, which is a reservoir, was designed for a certain level and should never be allowed to rise above it. "The water has got to be released or it could be damaged.

"The dam is therefore not working according to design, since if the inflow by rainfall is greater than the outflow the reservoir will be full," he said. And "if the land level is 52-53 GD and the reservoir is 59 GD, water will go into those areas."

The engineer agreed with Latchmansingh in the sense that "based on the capacity of the pumps and the sluices they [the authorities] should say how fast the water goes down." He also stated it is necessary to find out what is the present level of flooding.

He suggested this is why all the houses built in colonial days were elevated more than four feet above the ground. He noted that the builders at that time were catering for flooding, while the canals were there to store water. The engineer was of the opinion the Central Housing and Planning Authority should stipulate a certain level for all lower flats. "Since it is unfair to have people building knowing that there is a risk their properties would be flooded."

He mentioned that new lands were added to the system in South Georgetown and did not cater for drainage. He said drainage needs to be designed for one flood in 50 years and must involve the maintenance of sluices and drains. Also, the people "must be educated not to dump waste into the drains."

According to Phillip Allsop former chief works and hydraulics officer, the East Conservancy Dam is very long and runs in a very rough semicircle from the Land of Canaan to Cane Grove. The critical section runs between New Hope and Cane Grove. The crown dams run from east to west along the front of the dam. Water is fed into the conservancy from the backlands, through the rivers, which flow from south to north.

In his opinion if there is seepage then it is a serious problem though he noted that some dams are designed for this with trenches to collect those waters that are running out. Allsop said the conservancy "has a greater amount of water than it ever had. "The only solution is to raise the dam to contain a certain volume. This may be difficult because the slope would have to be changed to adjust to the new levels." Another solution would be to dam up one or two of the rivers flowing toward the conservancy.

Meanwhile, Chief Hydraulic Engineer George Howard said, "it would appear as if the rainfall exceeded the capacity of the system. And the system was not designed to take off that amount of water. This was compounded by the overflow of the conservancy and crown dams."

Howard said the East Coast is the lowest area along Guyana's coast. Guysuco is some 50 GD with Buxton also in the low 50s. This compares to a 56 GD high tide making it difficult to drain by gravity. He noted that pump stations were installed around the year 1920 because it was realised that gravity alone would make it difficult to drain the land. Therefore, "even if everything was working as it should, there would have still been problems," Howard said.

Speaking about the conservancy he said it has a full supply level, the purpose of which is to supply irrigation, navigation and drinking water. It also performs the "function of flood control because of the hills and swamp. The conservancy would discharge this [backland water] in a controlled manner."

Howard said in theory there were several things that could be done. "One of the things to look at is the operating of the conservancy," for instance, "at what level should we store water. Increase the number of drainage outlets, raise the dams, and store the water at a lower elevation level," because, "the material the dam is founded on, pegasse, would dry and crack in dry weather and in wet weather it can blow out. It needs to be continuously topped up. The alternative is to build another dam, damming the Mahaica river and feeding it into the East Demerara conservancy.

Yet another experienced engineer, while noting that the sluice at Garden of Eden allows water to flow from the conservancy into the Demerara River, said this sluice is not working at full capacity. The conservancy dam is supposed to be managed to flow into the Mahaica and the Demerara rivers, he said. At one time rangers were placed there to run the dam everyday. He said they were really glorified security guards who would inform the authorities as soon as they noticed something was wrong with the dams.

He said the critical thing with the East Coast is that the water there has to be pumped out. Referring to the pegasse material of the dam, he said this would always seep, but what, "you worry about is a breach."

[Editor's Note: Article first published under different title in Stabroek News on January 25, 2005.]