A portion of a wall of a water reservoir that was built during the British period and is located under Mohammad Ali Park on Central Avenue collapsed on Sunday morning, engineers blaming unplanned and unscientific beautification for the mishap.

An engineer of the Calcutta Municipal Corporation (CMC) said layers of soil had been dumped above the reservoir to raise the height of the park “without any attempt at finding out whether the boundary walls or the underground reservoir would be able to bear the extra load”. Many of his colleagues echoed him.

The floor of the park is now more than 7ft above the footpath outside.

A portion of the brick-and-mortar reservoir, which can store 3 million gallon water, became exposed after the 7am collapse. The civic body started erecting a wall to block the exposed portion of the reservoir.

“An 18m-long stretch of the wall along CR Avenue collapsed. We suspect the wall failed to bear the weight of the additional layers of soil dumped over the decades,” another engineer said.

The reservoir, with an arch-shaped roof, is being used to store drinking water since 1998, when a booster pumping station was set up on the park premises. Before that fire tenders used to draw water from the reservoir.

“There was hardly 2ft of soil above the top-most point of the arch in the 1990s. Now, there is more than 4.5ft of soil,” the engineer said.

“In the late 90s, the wall rose at least 2 ft above the floor of the park. Now, the park floor is at least 1ft above the wall because of dumping of soil.”

The park, maintained by the parks and squares department of the civic body, has shrubs and trees and a playground with places to sit.

The 40,000sq-ft park includes a children’s corner spread across 10,000sq and another 10,000sq-ft space for women and the elderly.

A civic team removes debris from the site where the reservoir wall collapsed. Picture by Bishwarup Dutta

The park underwent renovation at least once in the past decade.

A CMC official said layers of soil had been dumped on the park both when the Left Front and Trinamul were in charge of the civic body. “Councillors and borough chairpersons from across Calcutta demand beautification of open spaces. Mohammad Ali Park is in the heart of central Calcutta. There has always been a demand for its beautification. Dumping soil is part of the beautification drive,” the official said.

Such drives were carried out, the official alleged, often ignoring warnings that the additional weight might crumble the reservoir or could lead to the collapse of the walls.

“What could an engineer do if councillors keep demanding beautification in their areas,” the official wondered.

To make matters worse, the walls of the reservoir at Mohammad Ali Park were plastered during Durga Puja last year. The plastered surface, 2.5-inch thick, was decorated with reliefs of various figures.

“Had cracks appeared on the 20-inch-thick wall, they got covered by the plaster. If the cracks were visible, engineers might have been alerted about a potential disaster. The wall could not have collapsed without signs of stress, such as cracks, appearing days before,” a CMC engineer said.

CMC officials admitted they were lucky that no one was on the footpath when the wall with the iron railings on top of it collapsed.

“When we first heard about the collapse, our first concern was whether anyone had got trapped under the concrete and iron debris,” an official said.

Engineers were also worried whether the reservoir had developed cracks because of the addition of load on it over the years.

On Sunday, they saw wet marks at several places across the park. Since the entire park was not wet, engineers suspect water was leaking from the reservoir.

Residents of the area said debris of the wall had spread on the adjoining footpath and almost half of the Esplanadebound flank of CR Avenue. Civic engineers started erecting a wall on Sunday evening to block a portion of the reservoir that had become exposed because of the collapse.

“Engineers will do a thorough inspection of the reservoir to find out whether it has developed cracks.... We will have to remove a few layers of soil from the park’s floor to

ensure the reservoir is safe and it does not collapse,” the official said.

The reservoir, which was constructed before Independence, and the booster pumping station at the park receive water from the Tallah tank, in north Calcutta.

Because of the long distance between Mohammad Ali Park and Tallah, the pressure of water in the underground pipelines drops.

The booster pumping station was constructed to increase the pressure of the water flow. Large parts of Burrabazar and Mechua receive water from the Mohammad Ali Park booster pumping station.