Over the summer we dug a test pit into the limestone to check ground water availability for filling the wildlife ponds. It is also a possible support option for keeping wetland water bodies topped up with water through the Spring when other sources may be limited. The natural coralline limestone is just 15cm below the topsoil and is very porous, with winter water tables being drawn up close to the surface even at the top of the site. However, about 2m below the surface there is a very hard layer of impermeable limestone which we were unable to break through despite a 20 ton digger. Summer water levels dropped below this but are rapidly rising again with the change in weather, so the ‘well’ is of some use for the original purpose.
Having installed a vertical 2m long pipe into the well, we back filled with gravel to ensure good flow of water from the surrounding limestone and refilled. The well will be a good indicator of groundwater levels for the site as well as providing an emergency water source when needed. As part of larger projects on the site we will be looking at the practicality of much deeper (20-30m deep) boreholes in the limestone to tap into deep aquafers to supplement our need for reliable water volumes.
Reserves Manager at the Kingfishers Bridge wetland creation project in Cambridgeshire.