Claims that nearly 1,500 people could perish if a catastrophic storm hits Hampstead Heath have been greatly exaggerated, critics of the controversial dams project said this week.

The architects of the £15million proposal to rebuild flood defences across the Heath – transforming the cherished landscape – were accused by the Heath and Hampstead Society of overstating the risks of a severe storm in order to justify the scheme.

The society, which was founded in 1897 with a mission of safeguarding the Heath, said the City of London Corporation, which manages the Heath, is relying on advice from engineers that is “based not on the facts as they are recorded, but on computer models invariably using only the worst case assumptions of total dam collapse”.

The conservation group is urging members of the community to attend a public meeting on Monday at St Stephen’s in Rosslyn Hill, Belsize Park – the day before a public consultation exercise is to be launched by the City – to voice views on a project that has been branded the greatest risk to the park since the 1800s.

In a statement issued on Tuesday, the society said there have never been any flood-related fatalities or breaches of the dams in their 300-year history. “The society believes the engineers exaggerate the risk to justify the proposed huge dams,” it added.

The Corporation wants to build “huge” dam walls around some of the ponds, the largest of which will be an 8ft-high embankment on the Highgate Boating Pond and an 18-ft high one above the Mixed Bathing Pond.

The Heath and Hampstead Society said: “These works will permanently disfigure the Heath landscape. The City’s enthusiasm for them, when there are alternatives to what the engineers are proposing, is incomprehensible.”

“The City is unreasonably relying solely on the views of specialist reservoir engineers whose advice is based not on the facts as they are recorded, but on computer models invariably using only the worst case assumptions of total dam collapse: that every dam in every pond would breach instantaneously and simultaneously.”

The society also questioned why the City is not exploring an early warning system that could protect downstream communities in places like Gospel Oak, which are said to be under threat from a “one in 400,000 year” storm.

It also criticised the Corporation for presenting the works as a “makeover”, with talk of a new tree-studded peninsula being created at the Model Boating Pond.

“A new pond island, different grasses and more ducks do not stop flooding,” it said.

A spokesman for the City said: “The City of London Corporation’s public information giving and consultation exercise begins on November 26. Any and every public input into that is not just welcome, it is essential.”

The public meeting is at St Stephen’s from 8pm on Monday (November 25).