The report, which refers to the thoroughfare of streets 93, 86 and 70 and includes plans from the municipal Department of Public Works, says that piping already installed and more piping proposed at the time was too small to handle the potential flow.

“Based on the currently installed 1500mm-diameter pipe and the proposed design for an additional 800 meters of 1200mm-diameter pipe to be installed, the finished system will not have sufficient capacity to handle a 5-year storm episode,” it read.

Residential areas east of Street 93 sit about 5 metres below the primary Boeung Kak concession area, the report says.

“These low lying areas are at significant risk for flooding, loss of property, and potential loss of life,” it adds.

According to the report, Shukaku was told “during a face-to-face meeting by referenced sources . . . that the local government and municipality did not prepare any calculations prior to the start of their design and construction work”.

“Without any supporting calculations, they basically made a guess as to what size the drainage pipes should be.”

Shukaku, chaired by CPP Senator Lao Meng Khin, paid $79 million for a 99-year lease of more than 100 hectares at Boeung Kak in 2007. About 20,000 people have been evicted to make way for a planned commercial and residential project.

The company filled in the lake over the course of more than three years, and remaining families continually report flooding when it rains.

A man examines a pool of water in front of his house in Srah Chak commune yesterday afternoon. Rain from last week has yet to drain from parts of the commune. Heng Chivoan

While City Hall has claimed that Boeung Kak lake was not “playing a role as [a] rainwater reservoir”, Shukaku’s report says that the purpose of the drainage system at the edge of the concession was to “assist with rainwater collection that originally flowed into the closed lake system”.

Shukaku was funding City Hall’s connecting drainage project at a cost of about $246,000, the report says.

City Hall spokesman Long Dimanche yesterday declined to comment on the report and whether plans had been changed to respond to Shukaku’s concerns of fatal flooding.

“Technical experts are conducting studies on the project with the Shukaku company,” he said. “This issue cannot be solved in only two or three days, they need a long time to do it.”

Sam Piseth, director of the municipal Department of Public Works and Transportation, could not be reached for comment.

Shukaku announced last week that it would begin building its own drainage system at the site this month.

“Despite the efficiency of our drainage system, the rainwater will not be able to flow out effectively unless City Hall improves the external connecting system,” Shukaku spokeswoman Amu Pillay explained in an email to the Post last week. She was out of the country and unavailable for further comment yesterday, while other representatives declined to comment.

Seven Boeung Kak lake activists were arrested last month and imprisoned for one year just 24 hours after a protest outside City Hall in which they complained of constant flooding in their villages.

In houses at the eastern edge of Boeung Kak yesterday, families were still treading carefully around pools of water that remained around – and even inside – their homes from storms last week.

A man was working on part of a drainage pipe that appeared to be on company property and was snaking its way towards the road, seemingly to connect with a public system. He told reporters he “did not know” who his employer was.

A resident holding a small baby nearby said he feared the work would result in his house being flooded more than was already usual.

“My house floods every time it rains,” said Pich Pon, 56. “When it starts raining, I have to prepare my valuables. When there’s a lot of flooding, I go to a guesthouse.”

A few streets east, towards the back of Calmette Hospital, villager Phuon Thong spoke of his challenge when it rains: evacuating dozens of live chickens he raises in his house for the market.

“We have to turn off our electricity . . . and move to stay with family,” he said.

Surrounded by small children, Thong pointed to a metre-high line on his wall to indicate recent water levels.

“City Hall has never told us anything about fixing this problem. We were never flooded before the lake was filled in.”