The bat cave sits in a trench dug into the solid limestone, this provides perfect conditions for a bat hibernaculum, however it also sits bellow the winter water table on the site. I previous years this has been kept low by pumping the water out, however with the extreemly wet conditions this summer and autumn the pumps have failed to keep up with the flooding. At times the cave has been full of water from floor to ceiling, obviously disasterous for sleeping bats.
This drainage pipe laid underground from the floor of the bat cave down to the lower level ditch system should constantly and reliably drain the cave throughout the year.
The only problem is that the cave floor is about 4 meters bellow ground level, and the limestone is surprisingly hard!
The Sand Martin Cliffs here at Kingfishers Bridge have been a hugh success in tha past, however over years the face has gradually crumbled away through frost action and resulted in the vertical face becoming a slope. This allows predators such as stoats to get into the Sand martin holes. The Sandstone also retains moisture much more than the sand banks normally used by the martins. This year no Sand martins nested here for the first time since the project started
By removing the topsoil and laying a plastic membrane that slopes gently away from the face of the cliff, water runs back through the soil and not over the face keeping the face drier, this should minimise the frost action and also create better conditions for Sand martins to nest. The face then needs to be re-cut to vertical, easier said than done in limestone!