Play equipment has already been ordered for installation in May, but man-made tunnels and structures beneath the park, close to Carr Lodge Mansion, need to be located before work can begin.

A freshwater reservoir and a tunnel leading from it still exist beneath the ground and a sonar map of the ground is needed so building contractors can avoid them.

Local historian Christine Cudworth said, “It is thought that the reservoir was constructed at the same time as Joseph Bayldon built Sunroyd House, the name being changed to Carr Lodge after his death.

“Both my husband and I have been transcribing diaries written by Mary Carr, who married John Carr, named after his uncle the architect John Carr.

“In the diaries we have found references to the cleaning of the freshwater reservoir at Carr Lodge in the 19th century.”

She said that in July 1970 there was the threat of a water shortage and it was necessary to conserve water supplies.

It was intended to hold a model boat regatta at Horbury Gala, but the paddling pool was empty and permission could not be given to fill it up. But an old Horburian directed the town’s surveyor at the time to the site of the underground reservoir and as a result the paddling pool was filled with water.

She added: “The reservoir is large enough for a person to stand almost upright. The water reaches the reservoir through a long passage and it is important that this is located in order to avoid any damage or subsidence caused by work carried out above ground.

“There are also several capped wells and other water drainage channels running across the park.”

The work has been undertaken as part of the development of a Heritage Lottery ‘Parks for People’ application.

Steve Openshaw, a geophysicist from Bentham Geoconsulting Ltd, which is carrying out the work, said: “When planning for new facilities or improvements to Carr Lodge Park it is important to know the location of any underground tunnel or reservoirs or if there are any features of archaeological significance.

“If some historical features are found, it may be necessary to carry out further investigation in the future.”