Recent InitiativesRiverbank Revetment at Great Meadow | Log & 'Xmas tree' Revetment | Instream Enhancement | Management of Riparian Trees | Santon Weir | Potential New Angling Scheme
Riverbank Revetment at Great Meadow
This section of bank above the weir at Great Meadow on the Silverburn River had previously been protected using stobs and mesh back-filled with stone. Failure of the revetment had left a sheer, rapidly eroding bank and the potential for the stream eventually to migrate such as to bypass the weir.
After passing the test of a very wet winter, a selection of Manx native trees and shrubs were planted along the site in February 2007 to further increase the bank’s stability and wildlife value.
Wildlife potential was further enhanced by the incorporation of a small backwater, seeded with a mixture of native marginal plants.
Coir roll is usually installed pre-established with marginal plants, which themselves act as an anti-erosion barrier. However, imported pre-established rolls would have entailed introducing plants not of Manx genotype so, for this repair, Manx native marginals raised by the Wildflowers of Mann project were planted behind the rolls in early spring.
An area has now been set up at Mullen-e-Cloie by Andree Dubbeldam of Wildflowers of Mann to pre-establish coir rolls ready for similar techniques to be employed by the Water & Sewerage Authority elsewhere on the Island.
The faggots used at Great Meadow were sourced from the UK. A more sustainable supply was subsequently identified in the form of willow faggots produced by the Manx Wildlife Trust. The Trust’s management of the Close Sartfield Nature Reserve had, for some time, involved a willow coppicing regime but, as there had previously been little use for the cut material, most of it was burned on site. The extra funds received by the Manx Wildlife Trust as a result of this initiative will further contribute to conservation on the Island.
Log & 'Xmas tree' Revetment
In September 2011, Forestry staff and the River Management Project Officer installed a short section of Log & 'Xmas Tree' revetment, a technique used extensively in Ireland, on the right bank of the Silverburn downstream of Silverdale Cafe. A double row of lodgepole pine logs protects the toe of the bank while conifer tops attached to the logs dissipate the energy of the flow and collect silt during high flows. The work was able to be done by hand thereby minimising costs and disturbance to the riverbed. Bay willlow slips were planted along parts of the section in November. If this small trial proves successful in stabilising the bank, further such sections will be installed at appropriate locations.
The lower reaches of several of the Island's rivers have been straightened in the past, which can reduce the diversity of in-stream habitat to the detriment of fish populations. For instance, such channels tend to be dominated by shallow riffle and glide sequences, and contain fewer pools than one would find on a naturally meandering river.
Simple enhancement techniques, such as this installation of a series of boulders on a 30m stretch of the Silverburn in autumn 2006 can sometimes enhance such areas. Flow is diversified, the number of available fish territories may be increased and spawning gravels collect downstream of each boulder. A fish survey was conducted prior to installation. Further surveys in 2007 and 2009 found a similar total number of fish but included more large trout and a small increase in juvenile salmon.
In October 2009, a channel constrictor was installed in the River Neb near Ballawyllin to create and maintain a new pool. Pools provide fish with refuges from drought conditions, are the main habitat for large trout, provide safe resting places for migratory salmonids, and the deep, well-oxygenated deposits of gravel which tend to form at the tail-end of pools also provide some of the most productive spawning habitat. The constrictor consists of a pair of triangular structures, which narrow the channel by 2/3rds at that point but flood over at high flows. Each triangle is made of faggots and coir roll, originally netted over with geotextile. However, the geotextile in this instance was found to be hampering establishment of vegetation and is to be replaced in autumn 2011 with a woven cover of live willow. Prior to installation, fish surveys were conducted immediately up and downstream of the site so that the impact can be monitored. Should the effect prove desirable, more constrictors may be built at appropriate locations in the future.
Plans are underway to try out other enhancement techniques at appropriate sites on the Island. These include the use of deflectors in a section of the Lhen Trench to increase spawning areas for brown trout and lampreys.
If you own a watercourse, which you think may benefit from enhancement, contact the River Management Officer on tel. 651544, email firstname.lastname@example.org.
Management of Riparian Trees
Overhanging vegetation provides valuable cover for fish. However, extensive stretches of heavy shade can limit salmon and trout populations by reducing the growth of algae on which many of their invertebrate prey feed. The reduced light can also limit the growth of herbaceous plants, which keep the banks stable. During winter 2007/2008, students and staff from Ramsey Grammar School helped the River Management Officer to coppice and trim bankside trees along parts of the Santonburn and River Neb.
This weir on the Santon Burn has been a major obstacle to migratory fish for over 200 years. Fish surveys and anecdotal information gathered during a farm watercourse survey in the catchment indicated that, in recent years, it had become almost completely impassable due to changes in the nature of the stream bed. Following consultation with the landowners and the Department of Transport (DoT), a proposal was submitted by the River Management Officer for building a bypass channel utilising the disused mill race adjacent to the weir. This was constructed by the Works Division of the DoT in March 2009, reopening several miles of excellent river habitat to salmon and sea trout.
Potential New Angling Scheme
A frequent comment from anglers who took part in the 2007 Inland Fisheries Customer Satisfaction Survey was that it can be difficult to find out where they can fish outside of the National Glens and members-only private beats. This is a particular problem for visiting anglers, who often do not have the time to track down landowners in order to check for permission. The current situation also limits the Department's ability to promote angling on the Island's rivers and streams.
The River Management Officer is exploring the potential for a new angling scheme on the Isle of Man whereby landowners/tenants of watercourses may opt to permit angling on a designated stretch of stream in exchange for cash redeemable vouchers.
Similar such schemes are already run by several Rivers Trusts in the UK. Anglers purchase vouchers in advance and place the appropriate number in a suitably placed box before starting their day's fishing. The owner/tenant of the beat may then collect the vouchers when convenient and redeem them for cash.
The scheme aims to provide a reward for good management of streams as well as assisting the Department in targeting habitat management and promoting river angling. Streams don't have to be large to be appropriate. Lots of those featured in UK schemes are narrow tributaries comparable to many private watercourses here on the Island.
If you would like to know more about the proposal, contact the River Management Officer, Karen Galtress, on Tel. 651544, email email@example.com.
For more information on existing UK schemes visit the websites below: