Habitat Management Plan, Gloucester AC Durbridge January 2015
We are the Environment Agency. We protect and improve the environment and make it a better place for people and wildlife. We operate at the place where environmental change has its greatest impact on people’s lives. We reduce the risks to people and properties from flooding; make sure there is enough water for people and wildlife; protect and improve air, land and water quality and apply the environmental standards within which industry can operate. Acting to reduce climate change and helping people and wildlife adapt to its consequences are at the heart of all that we do. We cannot do this alone. We work closely with a wide range of partners including government, business, local authorities, other agencies, civil society groups and the communities we serve. This plan is subject to land owner agreement and flood defence consent.
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Background The River Leadon The River Leadon rises in Herefordshire north of Evesbatch and merges with the River Severn in Gloucester. At over 45km in length the Leadon drains a predominantly rural catchment and the conurbations of Ledbury, Dymock and the west of Gloucester. Major issues within the catchment include; silt inputs from unsuitable land management, historic channel realignment for land drainage purposes, loss of floodplain connectivity through artificial flood embankments and periodic pollution events. The European Water Framework Directive (WFD) requires all European water bodies to reach good ecological status by 2027. Under the WFD classification system the River Leadon is currently classified as being in moderate condition. Elements contributing to this unfavourable status include invertebrates, macrophytes and phosphates. Fish populations within the River Leadon are currently classified as high.
Fig 1. Summary of how water bodies are classified under the Water Framework Directive. Ecological status is determined by biological, chemical and physical parameters. Fish constitute one part of the biological parameters. Other biological parameters include invertebrates, macrophytes and phytobenthos. Classification of a waterbody goes by the lowest scoring element, for the Leadon these are invertebrates and macrophytes.
Durbridge Fishery Gloucester Angling Club (GAC) currently leases three stretches on the River Leadon for both coarse and game fishing pursuits. Durbridge is the upper stretch and is regularly fished for the main target species of brown trout (Salmo trutta) and chub (Squalius cephalus). Durbridge fishery is dominated by overstood alder coppice, creating dense channel shading, resulting in a paucity of in-channel macrophytes. The channel is on average 7m wide, trapezoidal and of varying depths throughout. Adjacent land use is predominantly pastoral, although steep banks prevent unfettered access to the channel in most locations. From previous electric fishing surveys there are records of stone loach (Barbatula barbatula), bullhead (Cottus gobio), pike (Esox lucius), dace (Leuciscus leuciscus), chub (Squalius cephalus), brown trout (Salmo trutta), Eel (Anguilla anguilla) and brook lamprey (Lampetra planeri). In general, the Durbridge fishery contains a good range of habitats for all life history stages.
At the downstream limit of the fishery there is evidence of a range of channel features including a meander, deep pools and backwaters created by the root balls of riparian trees. Substrates are dominated by fine sediments with occasional gravel deposits suffering high sediment loadings. Densely shade is created by riparian trees and the ridge of Herridge wood.
Fig 2. Overstood alder coppice creating dense channel shading
Further upstream, the dense riparian tree cover continues, dominated by alder (Alnus sp), creating a series of backwaters between root balls. A lack of marginal cover within backwaters and pools increases the risk of predation. There is an opportunity within the redundant mill leat at Durbridge mill to create a valuable backwater habitat. The leat could be de-silted and installed with brashwood faggots to increase refuge habitat and encourage marginal vegetation to establish.
Fig 3. Redundant mill leat at Durbridge mill could provide a suitable fish nursery area
A redundant weir upstream of Durbridge mill has the potential to impede fish passage in low flow periods. However, the weir crest has slumped in various places providing sufficient flow to pass rheophilic fish species and eels. The weir pool is a key feature within the fishery providing the best location for suitable spawning substrates and juvenile habitat. High velocities within the weir pool mobilise fine sediments and create clean spawning gravels. On emergence trout fry require a plethora of marginal habitat immediately downstream of spawning gravels and adjacent to the flow to seek refuge from predation whilst simultaneously having good access to food drifting downstream. Therefore there is an opportunity to greatly enhance marginal habitats by installing brashwood faggots and deflectors which will maximise fry survival in the area. This should be the primary location for habitat enhancement works.
Fig 4. Weir pool providing optimal habitat for spawning and juvenile recruitment
Upstream of the weir, the Leadon becomes straight and uniform, dominated by deepwater and glide habitat. The channel is heavily shaded by overstood alder coppice and the habitat is homogenous. There is an opportunity to increase light penetration by coppicing single stems of the alder stools and using the material to install flow deflectors in the channel. This will help create diverse flow conditions and optimal adult trout habitat. A second weir pool, adjacent to Cutmill Farm, creates a more significant barrier to fish migration particularly in low flow periods. A variety of fish pass options could be designed to facilitate fish passage including a rock ramp or pre-barrages which are relatively cheap to implement. Funding may be available for this work but would be subject to land owner permissions. The weir pool creates additional suitable spawning habitat for rheophilic fish species. Existing installed habitat features provide marginal habitat for trout on emergence and can be augmented to enhance habitat availability.
An improvised field drain in an adjacent field is acting as a conduit for fine sediment which enters the watercourse in close proximity to spawning gravels. The provision of an area of wetland and online settlement pond would intercept run-off allowing fine sediments to accrete and thus reduce sediment inputs into the Leadon.
Fig 5. Improvised field drain acting as a conduit for fine sediments inputs
Upstream of the weir, the habitat becomes more variable with a return to diverse habitat features such as point bars, deep pools and backwaters. Riparian tree cover becomes less dense and more species rich with willow, alder, hazel, hawthorn and blackthorn present. A significant hazel coppice could prove a good source of material for brushwood faggot creation.
Habitat enhancement techniques Background A diverse habitat is required to ensure that any resident fish population is sustainable. Different habitats are required for each stage of a species life cycle. If any one of these habitats is lacking or of a sub-optimal quality then there will be a negative effect on recruitment and a decline in species abundance.
Fig 6. Diagram showing how habitat availability can effect recruitment within a fish population. If the habitat for any life stage is lacking this will ultimately result is less adult fish within the population, these are called bottlenecks to recruitment.
Brown trout have three distinct habitats requirements to ensure a population is selfsustaining: 1. Trout lay eggs on gravel substrates in nests known as redds and therefore 2. Once the fry have – coarse gravels, not too fast water, plenty of habitat complexity due to being territorial 3. Adult trout, deeper pools for resting, undercut banks tree roots some deeper water with flow Techniques 1. Flow deflectors Flow deflectors use the natural flow of the river to create pools and riffles. They work by raising the water level upstream of them thus providing slightly deeper water and encouraging siltation. Below the deflector water depth is reduced and water speed increases, this helps to expel any silt in the gravels present and can create a localised scour hole.
Fig 7. Diagram showing how appropriately positioned flow deflectors can create diverse flow conditions
Flow deflectors are generally made of hardwood logs which can be pinned in place using sweet chestnut, rebar and/or wire. One novel technique for securing in deflectors is the platypus anchor. These wire anchors can be driven into the bank and provide a secure point of attachment for log deflectors.
Fig 8. Diagram showing how to install a platypus anchor into the river bank
Once a deflector is suitably secured they will remain in situ for many years and will not exacerbate flooding. NB. Flow deflectors must be put in appropriately positioned or they will have no benefit to the ecology of a watercourse and may increase bank erosion.
2. Faggot bundles Brashwood faggot bundles are inexpensive and easy to make when clearing fishing pegs at the start of the fishing season. They provide excellent habitat for juvenile fish and numerous invertebrate prey species and can also be used to protect eroding banks. Brash wood faggots can be comprised of any small diameter twig (10-50mm) with alder (Alnus sp) being the favoured species as it does not readily decompose in water. Willow (Salix sp) is the ideal species for bank stabilisation as it will root and consolidate over time.
Fig 9. Series of brash wood faggots pinned into the edge of the channel to provide juvenile fish habitat and bank protection
To make faggots, a saw horse should be constructed out of wooden stakes to make a suitable platform for loading small diameter twigs. Once the bundle is approximately 30cm in diameter it should be tied with biodegradable twine every 30 cm to ensure structural integrity.
Fig 10. Sawhorse used to tie brashwood faggots
Brashwood faggots can be a range of sizes, made to fit the habitat they are to be installed in. Typical dimensions are 1.5 - 2m in length and 30-40cm in diameter.
Fig 11. Schematic of brashwood faggot dimensions
3. Gravel introduction Gravel riffles are an important habitat feature for all gravel spawning (rheophilic) fish species. On natural lowland rivers they should generally occur about every seven widths of the channel usually on straight sections and at the entrance and exits of bends. However in many rivers, including the River Leadon, these habitat features have been lost through channel realignment with the aim to increase the capacity to convey floodwater. On the Leadon it is unlikely that riffle pool features will return naturally due to the underlying geology, and therefore the artificial introduction of gravel is a viable option. The length of each gravel riffle should be a minimum of two times the channel width, and a length of 15-20m is not uncommon when the opportunity to create a series of ideally spaced riffles is not an option. For trout, a gravel size of 7.5-75mm diameter is ideal as spawning substrate. The cost of gravel can range from ÂŁ15 - ÂŁ30 per tonne depending on the source location, and installation costs are highly dependent on site access. Further guidance on the installation of gravel riffles and possible funding sources are available from the Environment Agency.
Fig 11. Some examples of suitable riffle placements
NB. The installation of gravel riffles are subject to Flood Defence Consent. Any plans to install gravel riffles must be agreed with the Environment Agency 4. Tree hinging Tree hinging is an inexpensive and effective way of increasing channel cover and provides a good refuge from aerial predation, in addition to increasing light penetration. In channel woody debris can also create varying flow conditions and helps to vary bed profiles.
Fig 12. Tree hinging in practise, provides a good refuge from predation and diversifies flows.
Hinging involves partly cutting a riparian tree so that it is felled into the watercourse but remains attached to the stump. To ensure the tree is fixed in place, the stump can be drilled and a wire passed between the stump and the trunk, this will prevent mobilisation during flood conditions. Most tree species can be hinged into the watercourse although be aware that willow will continue to grow and may eventually choke the entire channel. 5. Willow spiling Willow spiling is used as an environmentally friendly method of erosion protection, and provides good marginal habitat once established. It involves weaving willow withies (thin willow branches) between fresh winter-cut willow stakes to form a fence-like structure. This method has the advantage that over time the willow roots and sprouts, providing living protection and additional stability. Care must be taken to use fresh-cut willow as dead willow will not sprout. In addition excessive shading from overhanging vegetation may affect the ability of the willow to establish. This method is suitable for the protection of steep or vertical banks. In some cases, a biodegradable geotextile (see below) may be needed behind the willow initially in order to prevent the loss of fine soil while the spiling establishes itself.
Fig 13. Schematic diagram of a bank protected by willow spiling
Willow spiling is an inexpensive method for providing erosion protection while retaining riparian and marginal habitat. It can also be used as a cost effective and sympathetic way of formalising coarse fishing pegs.
6. Tree planting Riparian trees are a very important part of the river ecosystem. The provide a source for in channel woody debris, a food source for many invertebrate prey species, refuge from aerial predation and keep rivers cool by providing dappled shading. On a trout river the ideal ratio of shading is approximately 70% shaded to 30% exposed.
Table 1. Summary of the benefits of riparian tree cover
Tree planting is relatively inexpensive and grants are available from various sources to increase riparian tree cover and thus resilience to climate change.
7. Online settlement ponds Field drains are a major source of sediment in a river system. Ditches, devoid of vegetation, provide a pathway for soils and fine sediments to enter a watercourse causing the degradation of gravel habitats. The provision of an online pool at the within a field drain provides a large low flow area which encourages fine sediments to accrete, thus reducing sediment loads in a watercourse.
Fig 14. Example of online settlement pond intercepting run off from field drain
In addition, the introduction of vegetation into a ditch network in the form of a swale will further attenuate flows and encourage silt accretion. Swales are shallow grass-lined channels designed to collect water and move it gradually away down slope. They can encourage infiltration along their route and the grass can provide filtration of suspended sediments, in addition to taking up nutrients. 8. Backwater fish refuges Backwater fish refuges are pools which are connected to the watercourse which provide an important foraging habitat for juvenile fish and also a refuge during periods of high flow. Backwaters are particularly important in watercourses which have been straightened for land drainage purposes, as there are very few places to seek refuge from the high flows that are synonymous with a straight river channel.
Fig 15. Example of a backwater connected to a watercourse which provides a refuge during high flows
Habitat management plan Part 1
Part 2
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Part 4
Funding opportunities Small scale habitat works can be achieved by organised work parties while carrying out bank side maintenance. Tree hinging, brash faggots and flow deflectors can all be installed at limited or no cost. Live stock management, tree planting, fish refuges and gravel introduction are more costly and may require help from external funding streams. Funding through Catchment Based Approach (CaBA) The Severn Rivers Trust has access to funding to implement projects on a catchment scale. There is currently an opportunity to develop a project to reduce sediment run-off in the lower Leadon which is a key pressure on the river system, areas of point source sediment pollution within the Durbridge fishery could be targeted as part of any project. Sport England Sport England is funded by the National Lottery and awards funding to improve or maintain a host of sports facilities. There are currently three possible funding streams: Small grant, Inspired facilities, Flood relief funds. These funding streams would be suitable to fund the creation of coarse fishing pegs. Facilities are more likely to receive funding if they are available to the public and therefore day ticket stretches would be necessary. Environment Agency Fisheries staff would be happy to help work up a bid if necessary. See website for details - https://www.sportengland.org/funding/ Environment Agency Environmental Improvement Grant The Environment Agency regularly have funding available to undertake environmental improvements in the local area, this can include livestock and riparian management as well as in channel habitat works. To apply for funding please contact Environment Agency Fisheries Staff. Catchment Sensitive Farming advisories A joint project between the Environment Agency and Natural England aims to deliver practical solutions and targeted support to enable farmers and land managers to take voluntary action to reduce diffuse pollution from agriculture. While this fishery does not fall within the priority area of the Leadon farm advisories may still be provided. For more information please visit the Natural England website – http://www.naturalengland.org.uk/ourwork/farming/csf/ Wild Trout Trust Habitat days The Environment Agency fund the Wild Trout Trust to host free practical habitat demonstration days for angling clubs across the country. These days are awarded on a first come first serve basis. To apply for the next round of free habitat demonstration days please contact Environment Agency Fisheries staff.