Update on water levels at Cresswell Pond
Monday 3rd June 2013
On Thursday evening (23 May) we were advised that water levels were getting high at Cresswell Pond and thus endangering the nests at the water’s edge.
An Estates Officer attended and ensured that the exit channel was flowing from the site. The water in the pond was not particularly high; the main issue was one of wave action on the strong north-easterly winds. It is believed that this wave action was responsible for the nests being washed out, although heavy rain and a high tide made matters worse.
It has been suggested that an attempt is made to drop water levels now, but there are two risks that arise from this action. Firstly the birds may re-nest lower and close to the new water level (putting them in an even more vulnerable location) and secondly that an upcoming spring high tide will wash into the pond through an opened channel. If a spring tide occurs in conjunction with heavy rain the water level will inevitably be much higher in the pond.
The management of Cresswell Pond is never an easy one. On the face of it, it seems very simple (though expensive and unsustainable) to continue to open the outflow channel, however the hydrology of the site and its existence as a saline lagoon has not arisen as the result of such interventionist management. The presence of the nesting birds further complicates the management such that non-intervention and intervention may each have unintended consequences and have no clear pattern governing success or failure.
Weather and tidal conditions have as much of an influence at Cresswell Pond as the condition of the outflow channel (which has an entirely natural tendency to become blocked). The SSSI status of the site includes a consent to undertake a limited number of channel clearances and is timed to include spring and autumn migration - other clearance can be carried out when the road is threatened. Any other works may require Natural England consent.
These bird species, by their nature, nest in a niche range near the water’s edge and are thus vulnerable to water fluctuations. Management is put in place to attempt to provide long-term sustainable management of sites and, unlike many specially created and designed sites, there is no mechanism available for day-to-day water level management.