The Arne peninsula in Dorset juts out into Poole Harbour, separating the Wareham channel from the main body of water. Right out at the tip, concealed by the remains of ancient oak woodland, lies a former ball clay pit.
The extraction company Imerys finished mining the deposit in 2008, and since 2010 have been restoring the area as part of their mitigation agreement, before transfering ownership of the site to the RSPB, who manage the surrounding nature reserve at Arne.
I was asked to document this reclamation process on behalf of the RSPB, in particular the flooding of the claypit basin with water from the harbour to create a saline lagoon habitat for wading birds and other species.
With mining activities ended the pit was re-profiled with heavy earth-moving equipment, and a layer of topsoil deposited above the expected final water level in the summer of 2011.
Next a channel was cut through the embankment to join the claypit with the harbour at the south end of the site. On especially high tides the water from the harbour would flood this channel to gradually fill the lagoon.
This process was expected to take many months and it was decided to document the process with a timelapse camera.
We surveyed the best location for the camera – somewhere with a wide view of the pit, a glimpse of the harbour in the background, a small island in the middle ground and some vegetation in the foreground to provide varied visual interest.
Unfortunately this necessitated pointing the camera due south, so we also calculated the position and angle of the sun in future months to try to minimise its dazzling effect on the camera’s lens and sensor.
The pit itself is off-limits, but there is public access to the surrounding area and it is too remote to monitor. Exposure to the elements over such a long period was also a consideration, so an expensive DSLR setup was not a practical option, and a relatively cheap-and-cheerful alternative was sourced.
The pit filled much more rapidly than the engineers had predicted and in April of the following year, after only 7 months, the rising water had achieved its final level.
The following video sequence shows events over that period, compressed to just 1 minute, using stills taken at 3 hour intervals:
The island habitat is already frequented by shelducks, and sika deer regularly visit its shores. It will take longer for the waters to settle and for other species to establish themselves.
It’s hoped that the regular interchange of water with the harbour will prevent the process of eutrophication, which would otherwise make the lagoon inhospitable. The suspension of clay particles in the water can be a serious problem in this respect.
Whether this industrially exploited area becomes the wildlife oasis hoped for, only time will tell.
With thanks to Mark, Rob, Damon, James and Em at RSPB Arne.