Whatever happened to all that gravel?

Written by Charlotte Hitchmough.

In August the banks of the River Kennet in Mildenhall were lined with mountains of gravel, and those who travel that route, or live in the village will have seen that the gravel has gone, and the river has changed shape. The gravel, all 2,500 tonnes of it, was a key part of a large habitat restoration project run by ARK in stages over two years.

gravel on bankgravel on bankThis stretch of river has been impacted by man over hundreds of years, ever since the area was settled.  Aerial photographs of the area show multiple meandering channels as well as ancient drainage ditches and gullies across the surrounding fields. By studying historic maps we can see that over time man has concentrated the flow in to one main channel running alongside the road in order to feed the water mills at Werg and Durnsford. The rivers were changed again during the 1970s when thousands of tonnes of river gravel were dredged out by the rivers authority to deepen the channel.

All these changes have removed many of the river’s natural characteristics, reducing its value for wildlife. Redundant mill structures impound water behind them, making it slow down and drop out the silt it carries; and structures themselves prevent fish from swimming up and down stream.  Deeply dredged reaches have lost their natural river gravel bed, removing pool and riffle sequences and leaving no place for trout and grayling to lay their eggs.  Fish can’t spawn in silty river beds, and if they do the eggs are often suffocated by the silt.  Finally, artificially straightened and deepened channels leave the river with a uniform ‘U’ shaped profile with few places for wildlife to hide, and little variation in flow to provide for the needs of different fish species and ages.
 
So ARK’s project set out to make the river a better place for wildlife again.

Making the river passable to fish
eel tiles and fish baffles on weir faceeel tiles and fish baffles on weir face

 

 

 

To make the structures at Werg passable to fish and eels we have fixed eel tiles and fish baffles on to the surface of the weir.

 

 

 

 

New bypass channel at DurnsfordNew bypass channel at Durnsford

 

 

At Durnsford a whole new channel has been created to bypass the hatches to the mill pool.

 

 

 

 

 


Reducing the impounding impact of the Mill
At the mill itself we have cut a notch underneath the old mill wheel, so that water can flow under it, even when flows are low. This enables the whole river to be run lower and faster.  To allow this to happen without drying up a small side stream, considerable work was done last year to lower the bed levels of the side stream too.

mll before notch cutmll before notch cutnotch created under millnotch created under mill

Putting the gravel back

Gravel in to riverGravel in to river

 

 

Tonnes of gravel have replaced that which was removed by dredging, creating a better substrate for fish to lay eggs and water plants to set root.

 

 

 

 

 

 

Adding the wiggles

creating new bank shapecreating new bank shape

 

 

The very straight river edges have been made more sinuous by adding new hazel edged bank, and either filling behind with soil and the gravels dredged during the 1970s, or by using brush wood from the surrounding area.

 

 

 

 

 

Volunteering …

volunteer water vole surveyorsvolunteer water vole surveyors

 

 

ARK’s volunteers have played, and will continue to play an important part in the work. A team of local people have trained as water vole surveyors and completed all the pre-work surveys. Meanwhile another team will be working alongside River Keeper John Hounslow to finish the bank revetments over the coming 12 months. The site is already part of our riverfly moniotoring network and the volunteer surveyors will be able to compare before and after data as the work settles down. You can see most of the project reach from the bridge over the river at Werg, and next summer ARK will be organising another river walk hosted by Savernake Flyfishers so that people can get a closer look.

 

 

2015 River Walk2015 River Walk

Funding
The habitat restoration work was managed by ARK and funded by the Environment Agency, Natural England and Thames Water with support from Savernake Flyfishers.

If you would like any further information about the project please do get in touch, or come to our AGM on September 23 in Hungerford Town Hall at 7pm.



 

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