"FISHING IN DEVON" -- Crediton Fly Fishing Club

FISHERY PROJECTS PAGE 2

  • Trash Dam and Bank Clearance
  • Alder Root Disease and Bank Stability
  • Tucker's Weir

    • TRASH DAM AND BANKSIDE CLEARANCE

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    All fly fishing waters require some close season work to improve access both for the angler and also for upstream and downstream migration of fish.
    Our club is no exception. We have to cut back excessive vegetation on occasions where the trees encroach too closely on the stream in order to:

    1.) increase incident light,
    2.) improve access, and
    3.) enable a fly to be cast.
    Stiles are sometimes needed where local landowners have decided to erect stock fences.
    We also need to clear trash dams created either by fallen trees, or by farmers who annually provide a regular series of obstructions in their endeavours to prevent their livestock moving up or downstream from their watering places. These latter obstructions can be anything from a series of gates(23kb pic) to strategically places pylons. But the most common method is fencing wire stretched across the stream. These get conveniently forgotten by the farmer when he brings his livestock in for winter housing. The autumn and winter spates bring down debris which collects against these barriers (17Kb pic), and the force of the water often leaves them partially submerged the following spring.

    In 1997 we concentrated our close season work on a section of the Yeo upstream of Codshead bridge (76kb pic) , and also on improving access to the (29kb pic) Culvery, a tributary of the Yeo, so that the EA could get in later in the year to clean the gravels.Go to section on gravel cleaning
    Neither of these sections of stream had had any work done on them for 10 years, so we had to cut back the overhangs rather more than we would like. It is difficult to get the correct balance between providing access and reducing potential trout lies. Because we only work on a relatively small proportion of our waters each year, we find that so long as we are not too severe in our cutting, the loss of the odd overhanging lie is not too serious. There are more than enough in the adjacent reaches. These lies will redevelop by the start of the next season, if not before.

    In 1998 we concentrated on the upper sections of the Creedy (18kb pic) . We have invested in a STIHL HT 75 chainsaw mounted on a telescopic pole. (21kb pic). This permits us to reach branches that would be otherwise inaccessible except by ladder (21kb pic). Although such equipment might sound alarming, it is counterbalanced, and is probably much safer to use than a conventional chainsaw in this sort of environment. It only has a 12inch blade, so it is not intended for felling enormous branches. Obviously, we have had to carry out a risk assessment for its use, and produce a code of safe practice policy document. In the interests of health and safety, we have decided to extend the risk assessment and documents to include all the activities that our work parties are involved in. Currently we have provided these for the following activities:-


    We would urge any one else out there currently working on the river, and who has not already done so, to do the same.
    If you would like examples of these codes of practice to help you write your own, e-mail me. However I can accept no liability for such documents as they have been drawn up specifically for our own circumstances. You will have to do your own risk assessments prior to completing your own safe codes of practice.

    We are noticing an increased incidence of Root Alder Disease in riparian trees on all our streams, and this may affect bank stability and also cause tree-drop trash dams. This disease is dealt with in the next section.

    Here are a few pics of the work we did on the Creedy in early 1998:

    Before and After 1
    Before and After 2
    Before and After 3
    Before and After 4

    Work in 1999 started with clearance work on the R Yeo below Salmon Hutch in early January.     Although rainfall has been heavy this winter, and the rivers have been running very high, we have been able to turn out for work every sunday in January.     Despite the bad weather during the week, we have been blessed with reasonable weather each weekend.

    The pole chain saw has again been in continual action, and the acquisition of a dry suit has meant that we have been able to retrieve fallen branches from the river where it would have been impossible in the past.     So far we have spent four weeks working on stretches below and above Salmon Hutch Bridge, and three more downstream below Fordton.

    What to do with the cuttings
    In the past we used to cut up the trunks and branches, and burn the smaller wood.    These days we cut it up the same, but stack it all tidily on the bank above the flood level.     We usually stack it tight to clumps of brambles, or interwoven amongst tree trunks set back from the water's edge.    The branches are placed with the cut ends facing upststream, and the heaviest trunks placed on top to weight them down to prevent strong winds from re-distributing them in field and stream.     Care needs to be taken that these piles do not interfere with farming activity, and it helps if you have some sort of riparian buffer zone in which to deposit the trash.    We have found these woodpiles make excellent habitat for encouraging wildlife.     A couple that we created on the Creedy last year are already being utilised by otters on a regular basis.     So, if you can stash it safely, don't burn it.

    ALDER ROOT DISEASE AND BANK STABILITY

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    Root Disease of Alders (Phytophthora root disease)

    Here are some pictures of Alders that I took in February 1998. I shall post some pictures of these trees in full summer foliage later in the year.

    Historical:-

    This is a fungal disese which affects the root of the most common tree on the club's river banks, namely the Common Alder (Alnus glutinosa). It was first reported in alders in the UK in 1993, and it has been recorded with increasing frequency since that time.

    We were first alerted to look out for the disease by the Environment Agency in 1996. Since this time we have found it to be present on the rivers Creedy, Yeo and Culvery.

    The classical symptoms are set out in the NRA/Forestry leaflet "Identifying Phytophthora root disease of alder". The most obvious early signs are a thinning of the overhead canopy, with sparsely covered branches and smaller leaves which turn yellow earlier than their unaffected neighbours. In about 10% of cases there is a black tarry looking discharge on the tree trunks. Eventually the whole tree dies and the bank can become unstable as the roots rot away.

    The Phytophthora family is quite extensive. P.infestans is the cause of potato blight. The organism responsible for alder root disease is P.cambivora, which has been implicated in similar diseases of other trees such as beech, maple, sweet chestnut and fruit trees. It is thought to be spread by water. Currently no other vectors have been implicated in its spread, but it seems likely that there must be predisposing factors as yet undetected.

    Situation, Spring 1998:

    We were very alarmed to learn that our trees were infected in this way. Currently there is about 10% morbidity on the Culvery (26kb pic), less than this on the Yeo, but possibly 30% infection on parts of the Creedy. When I spoke to a fisheries officer who was on secondment from the R.Axe catchment recently, he said that currently up to 80% alders were infected and dying on parts of his riverbanks. When I asked him what the infection level was like 5 years ago, he replied that it was similar to what we now had on the Culvery (ie 10%). This was not good news.

    When we look back at the way Dutch Elm Disease decimated our countryside in the 60's and 70's, we are bound to draw a parallel with this "new" threat. Whether it turns out as bad or no, only time will tell. Elms were not so numerous on our river banks as the alders are. Nevertheless, during the epidemic there were several areas which suffered bank collapse and erosion when trees died and toppled over. (see Cheerful footnote)

    Our main hope at present rests upon our limited experience of the disease, and our belief that there could be situations where the expression of the disease is less severe than feared. The Common Alder does not seem to the most long lived of trees. Often in the past we have noticed that part of a tree will die, whilst side shoots will continue to develop into mature trunks in time. Thus it often appears that part of an alder is dying back as other parts are still fairly healthy. Many of these affected trees show similar symptoms to those diagnosed as suffering from Phytophthora infection (70 Kb). It may be that this infection has been undiagnosed in certain areas for far longer than was originally thought, and that some of the trees have developed a partial immunity. It is possible that it is only when the disease spreads to new areas that it expresses itself with greater virulence due to the lack of immunity in the previously unchallenged population of alders. If this is the case, there may be some hope that the severity of disease may lessen in time and not all locations will suffer equally harshly.

    We are currently enquiring through the internet whether this disease has shown up in the past in other parts of the world, and if it has, how did it express itself, and how long it took to run its course. If any one can add to our knowledge we would be very grateful to hear from you. Please e-mail me

    Mitigation:

    There are many possibilities.
    1.) Re-planting alders, further back from the edge of the bank. The worst affectd seem to be in the wettest situations
    2.) The planting of white willow (Salix alba) strips (41kb pic) in areas where dead trees have uprooted. These will root almost anywhere. It is best to use strips with very little vegetation on them, so that they will provide very little resistance in a flood and will not be washed out.
    3.) Hybridising with other alder species: Although the common alder is the only native species, there are three other species: the Green and the Grey and Italian alder (A.viridis, A.incana and A.cordata) which are quite widespread. Although these species are also susceptible to Phytophthora, it may well be that hybridisation may result in greater disease resistance.
    4.) Research is needed to investigate the predisposing factors responsible for the development and expression of the disease. If these can be established it may be possible to eliminate them, and greatly reduce the potential impact that this disease is likely to have in the UK and other parts of the world.
    5.) Perhaps a far off light at the end of the tunnel:-
    Unlike the Elm (Ulmus procera) which propagates vegetatively by sending up suckers, the alder also reproduces sexually which should mean that disease resistance will be naturally selected for as time goes by.

    Cheerful footnote : )
    Each year we are noticing more and more elms (19kb pic) growing a little larger before they re-succumb to Dutch Elm Disease (19kb pic). Some are attaining a trunk diameter of >14 inches. We are also seeing the return of elm hedges in many places. Return to previous text

    Update:

    The Forestry Commission and the Environment Agency have produced a new pamphlet on the disease which should be available from the publications dept of Regional Offices. It contains an update on current scientific knowledge of the disease together with reasoned hypotheses on the origin, transmission, potential impact, and disease resistance. Brief guidelines are given for the management of alders on riverbanks, and a short reading list is appended.

    Suspected sightings of the disease should be reported to the area conservation and recreation office, although whether you get any feed back on this may depend upon the area in which you live.

    Further Update (30/05/99):

    In a recent publication, a spokesperson at the Forestry Research Station in Farnham has indicated that scientists at the Invergowrie Crop Research Institute have found that the causal agent of Alder Root Disease is in fact a hybrid of two introduced species of Phytophthora fungi.   One is P.cambivora which affects several broad-leaved trees; the other is P.fragariae, which is a serious pathogen of soft fruits such as strawberries and raspberries in N.America.   Normally fungi do not hybridise easily in nature, but because these two have come from different geaographical localities, they don't appear to have the inbuilt barrier to hybridisation that would occur in two different fungi from the same geagraphical location.
    Several strains of the new disease have been identified in Europe, with bad outbreaks of disease in Sweden, Germany, Austria, France and Holland.   It is now thought to be killing about 2% of Alders per annum.   Spread is via zoospores which are disseminated in water: consequently disease is mainly confined to bankside trees.   There is also a fair degree of regeneration via young shoots, so coppicing would seem to be advisable to retain some of the root system and improve bank stability.   If Alders are to be planted in a river corridor, they should be planted well away from the riparian edge.

    Further Update (10/05/2000)

    The Shropshire Hills Countryside Unit is currently promoting the Clun Valley Alder Charcoal Pilot Project. This will initially be a three year programme to re-establish the commercial use of riverside alders by:
    • Developing methods of harvesting and coppice management compatible with farming and landscape requirements.
    • Utilising new mobile charcoaling technology to process the linear resource efficiently
    • Developing new markets for home produced charcaol
    • Returning the riparian alders to sustainable management.
    This in turn should mean that many of the old and overgrown alders will be pollarded, stimulating fresh regrowth, which in itself should bring about an arrest in the spread and development of alder disease, and a marked reduction in the effects that the disease has upon bank stability.

    On Wednesday May 24th, 2000 an ALL DAY MEETING has been arranged at Chapel Lawn Village Hall, near Bucknell, Shropshire. This will include the following:

    • Presentation on Fishery Improvement by Ian Lindsay, from the Wye Habitat Improvement Project
    • Presentation + demonstration of Management of Riverside Alder and the role of Charcoaling, by the Clun Valley Alder Charcoal Pilot Project
    • Visits to demonstration sites on the Redlake
    • Feedback and further Discussion
    If you would like to attend the event, or obtain further information, email either
    Peter Norman:- (treescapes@ledwyche.u-net.com)
    or Andy Grundy:- (shcu@shropshills.prestel.co.uk)

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    TUCKER'S WEIR

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    SITE:-

    This weir is situated about 1/3 mile downstream from the top of the club's fishing on the River Yeo.

    Over the past 15 years there has been progressive erosion of the left bank immediately above the weir, and there evidence that the river has been continually trying to change its course during the past century.
    There have been several excessively violent spates in the last few years (21kb pic), which have led to weakening and undermining of the supports of the stone road bridge at Folly.
    This whole section of stream above the weir (17kb pic) is particularly attractive, and it would be markedly altered in character should the weir collapse.

    In the past, farmers have used all sorts of old rubbish to try to prevent erosion of the left bank above the weir. They have used vehicle parts, old milking parlour doors, rubble, in fact anything that they no longer had a use for and could not dump anywhere else. (17kb pic)

    Partly as a result of this ineffective bank maintenance Trees have now fallen into the pool (31kb pic) and there is danger of further bank erosion and undermining leading to diversion of the river to the left of the weir. This weir is passable by fish and provides oxygenation and an aesthetic interest to this stretch of river, and the CFFC consider that it is well worth preserving.

    ACTION:-

    • tree removal.
    • protection of the left bank with riprap.
    • landscaping.

    March 1999:

    Work has now started. The trees have been removed by Flood Defence, and repair to the banks upstream has begun.   -   pictures to follow

    Return To Top of this page   -   or Fishery Projects: Introduction

    or Back to Projects Page 1 for the following project details:

  • Gravel cleaning on the R. Culvery
  • Reducing channel width downstream of Codshead Bridge
    •

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