THREAT TO FLETCHING MILL WEIR:
ENVIRONMENT AGENCY’S PROPOSAL TO DESTROY ITS ENVIRONMENT
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History of the Site
Fletching Mill worked until 1939 before falling into disuse, leading to its demolition in 1951. East Sussex Record Office has a mortgage document dated 30 December 1703, but it is likely that the mill, and thus the pound above its weir, was built well before this date. When construction of the Sussex Ouse Navigation reached the Mill in around 1793 the pound was straightened and deepened in places, but the water level was retained since any change would have disrupted the mill’s water wheel. Thus the pound above Fletching Mill Weir has been at its present level for well over three hundred years.
After the Navigation closed the upper lock gates were replaced by sluices to retain the water level for mill operation. These sluices allowed a considerable proportion of the flow of the river to be passed along the former navigation channel to the west and under the road through the former navigation bridge. The original by-wash weir continued to carry the remainder of the flow through the narrow eastern channel and under the road in the far smaller arch bridge. More recently a concrete fish pass was built adjacent to the by-wash weir.
Fletching Mill Weir during it’s demolition in 1951
Recent events
Straw bales carried down the river on a flood in 2001 caused damage to the sluice, rendering it inoperable. A large steel plate was fitted between the upstream training walls of the lock chamber as a temporary cofferdam whilst repairs were organised. A large sum of money (believed to be in excess of £61,000) was spent on these repairs which included the provision of an electricity supply and associated control equipment to automate the operation of the replacement sluice gear. However, when the gates that had been ordered for the new sluice were delivered they were found to be incorrectly sized and would not fit. It seems that no additional money could be budgeted at that time to correct this error and the scheme was abandoned.
The existing steel plate has a small hole cut in it (roughly 30cm square) to pass compensation water down the former navigation channel. However, it passes far less flow than was previously the case when the sluice was in place, with the result that far more water is now being passed over the by-wash weir. This has had the effect of causing scour damage to the northern bank downstream of and adjacent to the weir. It has also overloaded the small arch bridge under the road, causing the road to flood more frequently than in the past and potentially endangering the stability of this smaller of the two road bridges.
Consultation
In March 2008 Royal Haskoning, on behalf of the Environment Agency, issued a consultation leaflet “Fletching Mill - What are your views?” to a number of local interested organisations and individuals. This described the events above with the notable omission of the abandoned repair scheme. It correctly summarised the present situation regarding the safety of the weir and the small, arched road bridge. It stated that the two solutions under consideration are “modification of the weir at the head of the bypass channel” and “re-grading of the by-pass channel” so “the water level would be gradually raised to that of the existing weir at the head of the by-pass channel”.
Roy Sutton, Honorary Consultant Engineer for the Inland Waterways Association, inspected the site, agreeing that the existing weir has been rendered unsafe and that the present arrangements put too much flow down the by-wash channel. His report dated April 2008 and sent to Royal Haskoning at that time, whilst supporting the general proposals made in the consultation document, also suggested a modification to enlarge the existing ditch across the site to divert a greater proportion of flow into the former navigation channel and under the larger bridge to the west, thus taking pressure off of the by-wash channel road bridge.
At a public consultation meeting at Fletching Village Hall on 8 September, 2008, Environment Agency and Royal Haskoning officials proposed a radically altered solution from that outlined in the original consultation leaflet. In this new proposal the weir would be completely destroyed, lowering the water level of the pound above the former lock and mill. EA staff present stated that the new proposal would improve fishing by removing a barrier to migration, that the new solution was ‘sustainable’ and that they were legally obliged to implement it. Bob Draper of the Sussex Ouse Restoration Trust and Roy Sutton were both present at the meeting and argued that this new proposal would (i) damage the ecology of the river and its surrounding land that has developed over more than three hundred years, and (ii) increase the flood risk in areas downstream of Fletching Mill, especially Uckfield and Lewes. Two riparian landowners and the farmer of the majority of the land, also present at the meeting, expressed their strong objections to the new proposal.
In an ill-tempered exchange it was stated that the situation had been made worse by EA inaction since 2001 whilst the full flow was passed over the by-wash weir and that the solution was contrary to EA’s own Catchment Flood Management Plan for the River Ouse and also their published national policy on the improvement of biodiversity and the importance of both the conservation and re-creation of meadows and wetlands for wildlife.
Ecology of the Surrounding Land
The area upstream of Fletching Mill is water meadow. It is grazing land at small freeboard above the stable water level of the river. Significant areas are slightly below the river level, draining into a parallel ditch that joins the by-wash channel near the smaller, arched road bridge. There are ox-bows where former loops of the river retain water throughout much of the year. The low freeboard causes the land to be inundated by flooding several times a year. If the pound above the weir were to be lowered this land would be permanently drained, destroying its fragile ecosystem. Before any proposal is taken forward a full environmental impact assessment should be undertaken that includes a specialist survey of the species in the riparian land upstream of Fletching Mill.
Risk of Downstream Flooding (especially in Lewes)
At present the combination of the weir/sluice and the small freeboard to the pound ensures that even relatively small floods overtop the banks above the weir, causing water to flood the water meadows, re-entering the river by flooding over the road or through the ditches leading to the by-wash. The present system ensures that the water that floods the meadows is delayed in its journey downstream. It does not reach the confluence with the river Uck, Barcombe Mill or Lewes until the peak of flooding has passed and the flood is thereby attenuated. If the weir is removed this water will form part of the peak flood, making the situation at Lewes worse than at present. The proposal is contrary to the need for upstream storage of floodwater presented in EA’s own Catchment Flood Management Plan.
Ecology of the River
The river impounded above Fletching Mill has been a slow-moving, deep channel for over three hundred years. It has developed an ecosystem normal to a slow moving deep channel. Lowering the water level would radically change it to become a fast-moving shallow river in a deeply incised channel and with a far poorer ecosystem very similar to that downstream of Sheffield Bridge. If (for instance) depressed freshwater mussel (a rare species typical of a slow moving deep channel) existed in the pound above Fletching Mill would the water level be lowered? It is essential that a full species survey be undertaken before this proposal proceeds.
Effect on Fishing
Royal Haskoning’s consultation leaflet “Fletching Mill - What are your views?” states that there is “limitation of fish passage at the site”, even though the fish-pass is in a good structural condition. It is uncertain on what facts this assertion is based. It is true that no salmonid migrations have been seen at this fish pass for a number of years. However, the local riparian landowners state that this lack coincided precisely with engineering changes made to the weirs and associated structures at Barcombe Mill a few years ago and the session of stocking sea trout smolts by the EA. Prior to those changes, regular salmonid migration activity was witnessed, apparently unhindered by the construction or condition of the existing fish pass. Thus the suggestion that removal of the weir would be an aid to fish migration appears to be false. There are many obstructions to salmonid migration downstream of the Fletching: the main reason why so few fish reach the site.
The destruction of the weir would in fact lead to the draining of the deep-water pound above, completely removing this prime habitat for coarse fish and thus having a distinctly negative effect on the coarse fishing presently practiced, with the fishing rights let to an Association.
River Naturalisation
It was argued by Environment Agency that lowering the water level would make the river more natural and that the river would, over the course of time, develop its own natural width, shape and ecology. That might be the case for some ‘river restorations’. However, past experience on the Ouse suggests that it will not happen here because the construction of the navigation in the late eighteenth century both straightened and deepened the river. The course of the flow is shorter and (unless it is restrained by barriers such as Fletching Mill weir) the river is steeper than it would naturally be. This results in the flow being faster and the river tending to incise itself far deeper than a natural river would. Once this has happened it cannot form the meanders that characterise a ‘natural’ river. Much of the course of the river between the site of Iron Gates Lock at Sheffield Park and Ardingly is straight, deeply incised, lacking ecology and passing flood flows extremely quickly and to most damaging effect. The removal of Fletching Mill weir and the lowering of the pound above it will lead to exactly the same effects here.
Alternative Solutions
We believe that Royal Haskoning’s current proposals are completely unsupportable for all the reasons given above. We gave tacit support to their original proposal given in their leaflet “Fletching Mill - What are your views?” for riffles to be created to raise the level of the river bed below the weir up to the level of the current weir crest in a smooth slope between the arched road bridge and the weir, adding to this the suggestion that the existing ditch across the site could be re-profiled to pass a greater flow from the bypass channel to the old navigation channel and larger navigation bridge, to alleviate damage to the smaller arch bridge. A possible issue with this latter suggestion was raised at the public consultation meeting in that there were concerns from some quarters as to the archaeological importance of the old mill leat that the ditch crosses. However, our consultant archaeologist’s opinion is that the size of the leat in profile and its original construction should be recorded precisely by taking a section across it as a part of the re-profiling exercise. There is no specific archaeological value in one section of the earthwork itself. Thus archaeology does not appear to be a true constraint on this approach.
In truth, of course, the best solution is for the Environment Agency to complete the schedule of works that they planned and began in 2001. That is, manufacture the replacement sluice gates to the correct dimensions, fit them and make the sluice fully operational again.
Pictures
The following pictures were all taken by Bernard Snell on 30 October between Fletching Mill and Sheffield Park.
Structures and channels in the immediate vicinity of Fletching Mill.
Existing water meadows and channel in the reach immediately upstream of Fletching Mill.
Incised channel in the section of river near Sheffield Park.
Response by Environment Agency
A letter, containing the information in the first part of this page, was sent to Environment Agency on 20 October, 2008.
Environment Agency replied on 27 November, 2008.
SORT’s initial comments; marked on EA’s reply prior to a full written response to them.