Sunday, 30 March 2014

Construction of the artificial Kingfisher nest bank at Hatfield Forest Lake.

The process started back in 2011 with the selection of a site and the application for a licence from Natural England.


The first stage in the autumn of 2012 was to clear the marginal vegetation from the bank of the Lake where there was a reasonably firm gravel base. A three-quarter inch plywood box was constructed, 8 feet long by 4 feet wide by 2 foot high. This was put in place and levelled. The base was then dug out inside and 20 sandbags filled with a dry mix of six parts of ballast to one part of cement placed as a foundation.
In the spring of 2013 several tonnes of ballast and cement were mixed up to form a basal plinth. The work was reinforced using a large quantity of old concrete fence posts.

The next stage was to build up a block work wall. 50 blocks were used, each block being 9 inches wide. As the block work was brought up reinforcement irons were placed inside to hold the sides in place and prevent spreading. The voids in the blocks were filled with a mixture of Type I stone and some ballast/cement mixture.


When the block work had set sufficiently a sheet of plywood was held in place against the front. A sand fill was then put in place consisting of soft sand 20 parts, cement one part. As the level of the irons was reached a layer of 10 parts of sand to 1 part of cement was used to stabilise the sand fill. Also, as the film was put in place some links of sink waste were introduced which could be withdrawn later on. These would form starter tunnels. 

Roofing battens were held in place using stub bolts previously set into the block work. On top of this was placed a green Onduline roof. It was organised so that there would be a good overhang at the front to prevent rain driving onto the sand fill and causing erosion.
Finally, a fence was constructed around the whole bank to exclude grazing stock and a plastic skirt attached to the plywood base to prevent rats and weasels climbing up onto the bank and into the nest tunnels.
The construction was carried out using volunteer labour from the National Trust with photographs by courtesy of Peter Matthams.