Experts: Like Patel Dam, this is why these reservoirs fail

As Kenyans came to terms with the tragedy that killed 44 people, with 40 others unaccounted for, and displaced 2,500 people, experts say there are many inter-linking factors that may have contributed to the incident.

Walls that had been dug around the dam, for instance, had been weakened over time and eroded to the dam’s capacity to hold any additional water that came with rains.

80M LITRES

“The water capacity of the dam could have been breached leading to the tragedy,” Grace Kagondu, a civil engineer, told the Nation.

During its construction in 1980, the dam, under Solai Stores owned by a Mr Patel (according to the Hansard), was allowed “2,500 gallons of water per day for domestic use and 40,000 gallons per day for irrigation of coffee, puffing and washing”.

But government officials said it had 80 million litres of water, 72 million of which poured out to the neighbouring villages, killing tens and destroying property.

And it appears that the Solai Dam is not alone in the flooding menace.

Of the 141 small dams that have been built across the country, Water Principal Secretary Fred Segor said, “90 per cent of them have been filled with water now that rains were pounding most parts of the country”— exposing the serious problem the government has to deal with now.

RIFT VALLEY

Ms Rose Wanja, a civil and structural engineer, with seven years of experience, suggested that the dam could have been overburdened by the volume of water due to the ongoing rains, fissures in the Rift valley belt, and the lack of routine checks and maintenance.

“A dam is a sensitive establishment and therefore there is need for routine checks and maintenance,” Ms Wanja said.

“This is to establish any points of weakness which include fissures, especially because water is able to find the tiniest cracks, consequently collapsing a structure.”

This, Ms Wanja said, was in addition to the tectonic activities happening in the Rift Valley where the dam lies, some 190 kilometers north-west of Nairobi.

“The fault lines may have affected the foundation of the dam, any small pressure at the bottom is capable of collapsing it,” she said.

RAINFALL

The National Geographic, in a 2015 article that examined the failure of earthen dams, suggested four reasons for their failures—  top among them being too much rainfall over a short period.

Mr David Adede, a geologist, agrees.

“Dams are just, naturally, walls built on a river to stop water at that point. At the point of heavy rainfall, it is possible for this wall to be breached, even more so in cases of earthen dams,” said Mr Adede.

But even then, long-term infrastructure problems also contribute to the disasters that are dam failures and overtopping.

The four reasons identified by the National Geographic are changes in land use like for example forests that surrounded the dams being turned into farms, or residential areas, changes in weather patterns, outdated dam designs, and lack of maintenance and funding, especially in cases where dams have been left in a state of disuse for so long.

CHINA DISATER

In history, the worst dam failure ever recorded was the Banqiao Dam Disaster in Henan province, China in 1975, and which killed 171,000 people, including those that perished following the famine and disease that followed the flooding.

The dam was a series 62 earthen water dams that tumbled during a severe typhoon.

The floods also killed more than 300,000 domestic animals, as many as 5.96 million buildings were destroyed.