ENVIRONMENTAL DAMAGE AS A RESULT OF THE FLOODING AT CAVENDISH MILL, AND INITIAL PROPOSALS FOR MITIGATION.

STONEY MIDDLETON AND CALVER MARSHES: ENVIRONMENTAL DAMAGE AS A RESULT OF THE FLOODING AT CAVENDISH MILL, AND INITIAL PROPOSALS FOR MITIGATION.
I visited the site on Wednesday 24th January with the aim of making a very preliminary assessment of the extent of the effect of the flooding and sift load on the water courses (Stoke Brook and its tributaries) and floodplain between Stoney Middleton Hall and the River Derwent.
Ecological Significance
This area has long been recognised as supporting a range of aquatic and wetland habitats which are amongst the most ecologically valuable in the Peak District including: • Priority national and local Biodiversity Action Plan habitats including Fen, Wet Woodland, Lowland Hay Meadow, Veteran Trees, Ponds and River Corridor. The area of fen and the Stoke Brook itself are recognised as being particularly important wildlife habitats. • Populations of water vole, a priority national and local BAP species, protected by law. These feed and breed along the Stoke Brook. • Bullhead and brook lamprey, two fish that are considered to be of European conservation concern, but have no legal protection outside of SACs. These are present in the Stoke Brook and the River Derwent. Brook lamprey create breeding nests’ in gravely areas of the stream bottom. The Stoke Brook is likely to be the spawning ground for many other of the fish species which inhabit the River Derwent, including those that are important to the fishery resource. • A range of less well documented species including water shrew, a local species with a poorly understood distribution, • A diverse bird assemblage including species dependent on the aquatic and wetland habitats such as the dipper. • A wide range of invertebrates including rare and uncommon species, associated with the Stoke Brook and the River Derwent, the stream-side trees and the fen habitats. These animals are the lower links in the food chain that support many of the mammals, bird and fish species associated with the stream and wetlands.
The majority of the floodplain land is managed within an agri-environment scheme. In addition works have been camed out in various locations designed to enhance or restore priority BAP habitats and so maintain or extend the range of priority species. These works have been funded through various sources including the Aggregates Levy Sustainability Fund and directly by the National Park Authority. Proactive environmental and awareness raising work has been co-ordinated by the Vision for Wildlife Project, a partnership project between the National Park Authority and Natural England. The whole area is managed as an informal local nature reserve with a steering group including landowners, naturalists and local people deciding on an annual basis a programme of capital works designed to deliver environmental benefit, and a programme of awareness raising events. As an example of the former we have secured funding from the SITA Trust for the construction of a further pond west of the Calver/Grindleford road adjacent to the stream. This is programmed to happen in the spring. As an example of the latter, Stoney Middleton school are working with the National Park Authority to develop a series of interpretation boards for the area west of the Calver/Grindleford Road including ones specific to the wildlife of the stream. This will complement panels east of the road constructed in partnership with Calver school.
Perceived Extent of the Damage
The following is based, as described above, on a brief visit. We may wish to modify the conclusions made based on further information becoming available, including the results of analytical tests of the silt and water samples.
It is impossible to see the stream bed owing to the silt load in the water. However silt brought down by the flood is plastered on the stream sides including banks and small flat areas normally above the water line at all times other than when the stream is at maximum capacity. There is likely to be a covering on the stream bed. In places the silt is over 30 cms thick. This will have had a devastating effect on all the aquatic and marginal habitats and the species associated with them including water voles, brook lamprey and bullheads, species of national and international significance.
Outside of the immediate environment of the stream the silt is restricted in extent. The exceptions are: 1. Relatively small areas adjacent to the stream where the flood has come over onto the floodplain and left a deposit of silt. This includes areas of fen habitat of high ecological value; 2. Areas where the floodwaters left the road, north of the small housing estate and close to Stoney Middleton Hall. These areas are of low ecological value but the silt deposits will have (and are having) an impact on the agricultural use of the land. 3. An ‘off-line’ pond to the north of the stream and the east of the Calver/ Grindleford road where silt appears to be covering a large part of the bed and the sides of the pond. The inflow is now completely blocked. Small areas of land close to the pond are also covered in silt where the flood waters have breached either the pond or the stream. This pond was constructed in 2004 using grant from the Aggregates Levy Sustainabilty Fund.
The impact of the flood will be not only in terms of the physical effects of the silt deposited on the stream and the land but also in terms of the potential chemical toxicity of both the waters and the silt. This could be assumed to be more widespread that the extent of the silt as the water may well have flowed further than the silt indicates. In addition and assuming that the toxic materials present in the silt are water soluble, we could expect these to be released into the stream and into groundwater over a prolonged period of time. High levels of heavy metals in the silt may have a localised damaging effect on plant and animal populations and so on the wildlife habitats, food chain and agricultural use of the land. High levels in the water will have more far reaching implications.
Priorities for Action.
For reasons described above these are our immediate concerns. We may wish to modify or add to these as knowledge increases and as the full impact of the flood becomes apparent.
1. The condition of the stream needs to be assessed in the light of the important populations of animals that it did support and particularly with reference to brook lamprey, bullhead and water voles. It is likely that a restoration plan and action will be necessary to ensure that appropriate habitats are re-instated to allow the re-colonisation of the stream by these species. This will have to include not only the physical habitats appropriate for their survival but also water quality and the habitats and species groups necessary for these species to feed. This proposed action plan needs to be developed and acted on as quickly as is feasible. For example Brook lamprey will start to return to the stream for breeding as early as April.
2. The ‘off-line’ pond will need to be re-instated to its former profile and condition. This is by far the easier part of these proposals but will require a restoration plan and action on the ground.
3. Works are likely to necessitate complete removal from the site of silt identified in the stream and pond restoration plans, owing to its physical and chemical properties.
Recolonisation opportunities
The small tributary stream of the Stoke Brook (shown on the attached map) is running with clear unpolluted water. In addition several springs which feed the marshes are also unpolluted. Aquatic plants and animals present in this stream and springs may be able to naturally re-colonise the Stoke Brook once restorative action has taken place. However populations of animals in this stream are different to the Stoke Brook. It is unlikely to support the whole range of invertebrates or fish fry present in the Stoke brook. It may or may not have provided a ‘safe haven’ for water voles. Survey for some or all of these species will be necessary if we wish to establish the complete resource of species for natural re-colonisation of the brook. One permanent pond and one heavily shaded seasonal pond lie to the east of the damaged pond, between it and the River Derwent. They may be able to provide species which can naturally re-colonise the damaged pond.
Other Interests
The assessment of damage outlined above does not include the potential impact of the event for grazing animals. Again this is likely to be two-fold, one in terms of the physical impact of the silt on the ground and secondly in relation to its toxicity and the toxicity of the stream which is the primary water source for the animals. The National Park Authority has outlined its concerns to the relevant landowners.
In addition the assessment only touches on the impact on the wildlife and ecology of the River Derwent or for the fishery implications.
Rebekah Newman 25.1.07 Vision Project Officer, PDNPA