The Final Day of Rivers Week: Volunteer Day Two

The second and last of the volunteer work days took place on the Thursday of ‘Rivers Week’, after I’d completed all the work that I waxed lyrically about in Rivers Week: Working Alone Again after the first day.

The primary task of the second day was to get the 15 cubic metres of new 40mm2 of gravel our of the 15 separate bulk bags into the channel in two separate places, and install a couple of large woody debris deflectors at the sites to sort and scour the gravel over time. The erstwhile Wild Trout Trust in the form of Andy Thomas took charge of the downstream area of gravel (7m3), whilst his colleague, Mike Blackmore started organising the upstream area (8m3) immediately downstream of the weir). I busied myself with finding some large woody debris items to install on the weir pool riffle, ensuring that a decent flow of oxygenated water would be channelled over the new riffle area, keeping the gravel clean, preventing deposition and encouraging spawning and egg survival in the future.

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My trusty Land Rover was roped into service to extract some large Willow logs from the stand at the other end of the estate and tow them up to the weir pool for this – avoiding the rather large and seemingly-unavoidable gatepost to which my Land Rover had been inexplicably and intimately drawn to whenever I drive through the gate into the paddock (hence the remodelling of the front nearside wing!)

One of the more useful tools around is a Stihl BT-45 2-stroke wood auger with a long 18mm wood bit for this job. Chestnut stakes are fantastic for installing woody debris and creating faggot or Willow spiling revetments in silty or sandy substrate. Anyone that has ever tried manually driving 4” round Chestnut stakes into a concreted gravel substrate with a post maul or post driver will tell you that the only outcome is usually a snapped post, sore shoulders and a penchant for walking around in the manner of the hunchback of Notre Dame for a few days.

An innovative technique I picked up a few years ago from the Wild Trout Trust involves using modified 16mm diameter by 1.5m long steel reinforcing bar (rebar – as used in reinforced concrete construction). These drive into gravel using a sledge hammer far easier than 4” round Chestnut stake using a post driver or post maul (even an excavator/tractor mounted post rammer struggles at times – normally the post snaps when the weight comes down due to the resistance from the gravel). 16mm diameter is about the right compromise between size and ease of use – as long as an 18mm hole is bored through the woody debris, they tend to work extremely well – all that is normally required is a large flat washer welded around the rebar about an inch from one end to prevent the woody debris simply lifting off.

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I had previously welded up stop washers on fifty rebar (just in case), and these were soon put to use once the gravel was installed. Essentially, the technique is to use the auger to bore a hole through the woody debris item in various places, manoeuvre it to the desired position in the channel and then use a sledge hammer to beat the rebar through the holes in the woody debris and into the gravel substrate. Not only does this achieve a very natural look (no fencing wire or wooden stakes are visible), but it also tends to be incredibly resilient to vandals and damage (and a lot quicker and easier to install in gravel). If the very top of the rebar (with the washer welded an inch from the end) is beaten into the woody debris, it is nigh on invisible on the finished result.

My work plan detailed that an ‘Upstream V’ type structure was to be installed on the new gravel riffle, immediately downstream of the weir. This structure would hopefully deflect / concentrate the flow of water across the new gravel, as well as scouring and sorting it with a higher flow velocity. Myself, Mike Blackmore and three willing Environment Agency volunteers manhandled the 8ft long Willow logs into the channel after I had drilled them at each end on the bank to work out the best positioning. (Any volunteers reading this will recollect that this was where I attempted to ‘catch’ one of the logs as it was dropped in – and merely succeeded in soaking myself). A quick demonstration of correct use of a sledge hammer later – and the volunteers set about beating the rebar in and raking the gravel about to spread it in the channel.

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Mike Blackmore busied himself with felling one of the Ash tree branches adjacent to riffle and installing it into the margins to create some much needed juvenile fish habitat. The idea of this is to allow the newly-hatched fish fry some protection in higher flows, as well as protection from adult fish immediately adjacent to where they have hatched from.

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Unknown to me, the group working downstream led by Andy Thomas were quicker, and had already installed most of their gravel alongside the faggots installed two days earlier – and a large woody debris structure on top of it! (My excuse was that the substrate was softer downstream!) This had created a lot of flow and geomorphologic variation in the channel, and hopefully the river will sort and scour the new gravel riffle over the next few years. The woody debris should also help prevent the gravel from simply washing downstream in times of high flows.

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Andy and his volunteers had not slackened off however – a limb from one of the riverside Willow trees I had part-pollarded was ‘hinged’ into the channel by Andy, and all the brash which had been left over was laid alongside and wired down by his active gang of volunteers to complement one of the large woody debris items I had installed the day before with the excavator. This had the same effect as the Ash branch Mike had felled and staked into the weir pool riffle, in creating some much needed marginal juvenile fish habitat downstream of the new spawning riffle for newly hatched fish fry.

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The day drew to a close with the Wild Trout Trust in the form of Mike and Andy providing some on-site commentary and showcasing of the work carried out, to compliment an excellent video diary and work plan created by Clearwater Photography that can be viewed here.

I think all that remains is for me to thank all the volunteers from various walks of life who willingly gave up their time, energy, enthusiasm, but retained their sense of humour for the two days, including those from the Loddon Fisheries and Conservation Consultative & Swallowfield Fishing Club. Special thanks must go to John Sutton, late of the Environment Agency Fisheries Team and now of Clearwater Photography for his expertise with a camera on the days, Mike Blackmore and Andy Thomas of the Wild Trout Trust for their expert advice and guidance, and Karen Twine and Tom Sherwood of the Environment Agency Fisheries Team for organising the Environment Agency assistance.

ACC.

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