The wetland restoration at Pondhead aimed to make the streams more resilient against our erratic wet weather by taking a natural approach to flood protection that re-connects the floodplain and restores it to its natural system. This work aimed to slow the water flow and improve grazing locally.
A careful review was carried out by experts and the flood risk assessment provided evidence that the restoration work will not increase the flood risk to local householders.
A topical survey was undertaken to clarify that there is sufficient fall in gradient for the scheme to function effectively. The site was worked in phases to make sure that the channels were operating as they should. We are also monitoring the location to see how it is responding to the restoration.
Pre-restoration condition of Pondhead, with riverbanks eroding, can be seen in the gallery below:
The site is made up of two Sites of Special Scientific Interest (SSSI) units, namely unit 386 and 387. Parkhill Lawn (the western portion of the site) is on the Open Forest, whilst Denny Inclosure (the eastern portion of the site) is Inclosure that has been thrown open to Commoners stock.
Both SSSI units are in unfavourable declining condition due to the effects of artificial drainage. Across Parkhill Lawn, the artificial drain line was not dug in the lowest point in the floodplain. Due to the limited gradient in the area, water tends to overtop the artificial drain and stand on the lawn for long periods of time. The Commoners Defence Association is concerned that this is negatively affecting grazing.
The western side drain arising from Pondhead Farm is deep and wide, with eroding banksides and large spoil heaps along its length. It is being colonised by trees and scrub, and is a hazard to stock. The second side drain less than 100m to the east is deeply incised.
Within Denny Inclosure, the artificially deepened channel is causing increased erosion within the riverine woodland habitat. As a result of this overdeepened (and in some cases straightened) channel and the associated spoil banks, there is limited seasonal inundation and inconsistent interaction with the floodplain. As a result, the adjacent riverine woodland habitat is negatively affected.
Across Parkhill Lawn, it is accepted by Natural England and Forestry England that complete infill of this stretch of dug channel is not acceptable to the Verderers and Commoners at this time. A compromise solution to restore the channel to the lowest point in the floodplain was agreed, which in conjunction with bed level raising and removal of spoil banks would focus water into one defined course through the floodplain. Ideally, from a wetland restoration perspective, both side drains would be infilled. However, due to the drainage requirements of the properties to the north of the site, it was agreed to retain the eastern side drain in its current state. Flow from the western side drain will be diverted across to allow this western channel to be almost completely infilled, restoring grazing and safe access for stock whilst reducing artificial drainage on the site overall.
Within Denny Inclosure, the bed level of the channel will be raised using hoggin, and spoil banks removed. Where evident, stretches of original remnant meanders will be incorporated, with subsequent infill of the artificial drain channel. The bed level of the last remnant meander just upstream of the Holmhill Passage bridge will be linked in to the natural bed level downstream of the bridge.
In addition, work will be undertaken to maintain or improve pedestrian and rider access. The two wooden bridges at SU31410683 and SU31750698 (both vehicle bridge width) will be relocated across the restored watercourse route, and a discreet gravel stock crossing will be restored just downstream of the confluence of the eastern side drain with the main channel, at SU31980687. The vehicle bridge at Holmhill Passage will remain in its present form and location.
Other management prescriptions that were agreed on the site visit were to fell encroaching birch, willow and scrub on the open lawn habitat.
Wetland Restoration at Pondhead –: The planning application for wetland restoration at Pondhead (Planning Application Ref. 15/00294) has been successful following further assessments that were carried out to respond to the issues raised locally. We gathered more information on the local drainage works along with undertaking additional survey and technical work.
Flood Risk Assessment
The comparison of the previous Flood Risk Assessment (FRA) and the updated FRA indicates that the old FRA was prepared using a standard and robust methodology and its conclusions within its scope and data availability were acceptable. A new FRA was prepared using the same methodology but benefiting from a more accurate dataset (i.e. a topographic dataset) of the channel incorporated into the hydraulic model. As expected, the updated hydraulic model provided more reliable water elevations as well as a more realistic understanding of the proposed restoration implications on water level changes. The new hydraulic model generally showed a reduction in water levels compared to the results of the old model, ranging from 0.37 to 1.51m along the channel network modelled. The updated FRA re-confirms that flood risk to the four closest properties (i.e. Matley Cottage, Pondhead Farm, the Lodge and Park Dale Cottage) would not be affected by the proposed restoration works.
There have been further representations received in relation to archaeology. These have been carefully reviewed and deemed to adequately address archaeological matters, and includes sufficient mitigation measures (e.g. a watching brief) to ensure that the works are carried out in such a way as to minimise any impacts on the local archaeological resource. This view is shared by the County Archaeologist.
A careful review has been carried out by experts and the flood risk assessment provides evidence that the restoration work will NOT increase the flood risk to local householders.
A topical survey has been undertaken to clarify that there is sufficient fall in gradient for the scheme to function effectively and we will work this site in phases to make sure that the channels are operating as they should. Furthermore, we will monitor the location to see the positive change after the restoration, both in terms of improving the quality of habitats and restoring the physical function of the river system.