Improving the River – Introduction

The gallant chaps of the Wild Trout Trust in my neck of the woods are the sort of unflappable types you need around when large gang of enthusiastic volunteers arrive all at once for a day to give you a much needed hand improving the fish habitat on your stretch of watercourse. This was ably demonstrated when on a grey & moody March morning, two dozen willing and able volunteers turned up to give me a hand with a project to improve 800 metres of the lower River Blackwater. This was the fourth year on the hoof that the local Environment Agency Fisheries Team, Wild Trout Trust and Hampshire & Isle of Wight Wildlife Trust had run their successful ‘Rivers Week’ in the catchment. Having been heavily involved with the previous four Rivers Week projects in a practical capacity, I am pleased to say that like a good wine, it has improved over time. Flood Defence Consent for all the work I had planned was granted by the Environment Agency, and with orders placed for 13t excavator and 6t dumper hire, 15 cubic metres of 40mm2 clean gravel, untreated chestnut stakes, steel rebar, geotextile fabrics and the ever useful fencing staples and wire, the practical planning and preparatory work started.

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This 800 metre stretch of the Blackwater is not a quintessential trout stream! Although John Sutton, one of the firm stalwarts of Fisheries habitat enhancement, proved by catching a lonely small wild Brown trout on his first visit to the river, the water quality has improved massively over the last few years. At the top limit of the land all the flow splits through two channels immediately upstream of an impassable crump gauging weir, and both channels historically have been straightened, dredged and impounded. Both homogeneous channels were deeply incised and trapezoidal, with a distinct lack of variation in depth, flow velocity, and habitat. Marginal vegetation was non-existent through most of the reach through a combination of over shading and vertical banks. Potential spawning habitat was very limited due to historic dredging and what gravel substrate remained had become choked through deposition as a result of the low flow velocities. Interestingly part of the stretch below the existing crump weir has only been around 40 years since a new channel and crump weir was constructed to create a better means of flow measuring in the 1970’s, and the original (if not natural) channel infillled and forgotten, along with a smaller distributary channel which used to flow across one of the fields. This area of newer channel contained the only viable spawning habitat in the reach – perhaps because it had not been dredged as heavily or for as long as the original channels. The site of the old, forgotten Victorian red brick and concrete weir still remains, underground, infilled with concrete, but the crest is just visible in the margins of one channel as a disused relic of a bygone age. (Perhaps a future project…)

Phase One of the project to improve the reach between the crump weir and the brick road bridge, and revolved around improving the connectivity with the flood plain, addressing the vertical incised channel banks, introducing some marginal and in-channel habitat, and improving the viable spawning areas in the channel. Much of the heavier work was undertaken by myself with the (delicate) use of a tracked excavator to push the banks in where I could, both narrowing the channel to increase flow velocity and providing some much needed marginal habitat, along with a more pleasant river bank for all. This also had the added benefit of reducing flood risk downstream as the limit of my land is marked by aforementioned elderly brick built and lined bridge with a very small arch. In times of high flows, this acts as an impoundment and results in the water backing up. As rivers are prone to doing, the water then finds an alternative route – unfortunately in this case it merrily flows along the road through the village. Due to the lack of connectivity, the flood storage capacity of the flood plain (of which the majority of my land is) had been greatly reduced as a result of the spoil from dredging being placed on the banks, creating bank heights higher than the surrounding land. (There was a berm comprised of around 30 cubic metres of gravel which had been dredged from the river, just upstream of the road bridge – taking up capacity in the flood plain!)

Much as I could do on my own, working the odd day between work off-site and at weekends – sometimes a few more (for few, read a lot more) pairs of hands are needed to really make a difference. In areas with slack, shallow margins, it was possible to delicately remove the top 3 or 4 inches of vegetation and roots with the excavator bucket, and slide this down the bank into the margins. This was in order to keep the roots intact, allowing marginal vegetation to be neatly transplanted from the top of the bank to the river as a slab – making it more likely to stay there and less likely to break up. The rest of the spoil behind was then removed to bring a gradual slop back to the bank, and the remainder compacted with the bucket to reconnect the flood plan and river channel (hopefully around what it should be naturally). In places, the banks were so high that pushing down the banks as described above with the excavator would have just resulted in whole sections of the bank washing away due to the lack of vegetation and root systems to bind it together. Some form of bank protection and structure was going to be needed to narrow the channel, increase the flow velocity whilst also retaining the structure of the bank to allow it to colonise over time without risking serious erosion. Along came Rivers Week 2015.

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To be continued!

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