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The photos below show a record of progress of the installation of a new combined canoe and fish pass at Eldridges Lock on the River Medway, 1 mile West of Tonbridge in Kent. These works are being undertaken in Autumn/Winter 2009.
This combined pass, the second of its type in the UK (the first being at Porters Lock just 1.5 miles downstream) is an 80 metre long concrete channel, 1.5 metres wide and 600mm deep. The difference between upstream and downstream water levels is 1.6 metres. the pass starts with an entrance pool that allows canoeists to line themselves up for the first slope. The first slope which is furnished with artificial reeds known as "fish brushes" runs for 20 metres at a gradient of 1 in 25. Canoeists then enter a 3 metre wide resting pool which runs level for 26 metres. At the end of this pool canoeists have room to line themsevles up for the final slope - again furnished with fish brushes. This slope is also 1 in 25 and runs for 20 metres. At the end of this slope the channel narrows to 1.2 metres. The reason for this is to provide a slightly greater water velocity at the exit which should provide good attraction flow for fish to find and then climb the pass.
The brushes within the pass perform 3 functions. 1. The brushes are soft enough to allow canoes to pass over them safely witout any damage. 2 the brushes are rigid enough to withstand water pressures and therefore provide eddies and back-currents to enable fish to climb the pass. 3. There are enough brushes in the pass to ensure that during low river flows the channel only demands 0.3 cummes (300 litres per second). This is essential for a river like the Medway which has a predominately clay based catchment with resulting low summer base flows.
To each side of the pass, the ground has been sloped at 1 in 3.5 and a Geotextile called Enkamat has been laid to reduce the risk of scour in flood flows.
The idea comes from the University of Kassel in Germany. The University has been extremely helpful in providing advice and guidance for this pass and Porters Lock Pass. The brushes have also been supplied by them.
The works have been designed by Halcrow Group Ltd and construction undertaken by Dean and Dyball Civil Engineering. The cost of the whole project including purchase of land, design, contract documentation, supervision, supply of the fish brushes and of course construction is around £200k.
The pass should be completed by Christmas 2009, but will not be opened until March 2010 due to the risk of flood flows causing damage to the freshly-laid banks of the pass. The banks rely on the growth of grass to "stitch" it together and as such this will not start occurring until Spring 2010. Until then, the gates of the adjacent lock will remain pinned open so that most flood flows will be pass through this route. Keep an eye on this website for updates.
If you require any further technical details of the pass, please contact Chris Downs at Halcrow Group 01732 424184.
For any details on canoeing on the Medway, please visit the Medway Canoe Trail website: www.medwaycanoetrail.co.uk
The plan of the works
Before works commence
29th Sep - excavation starts
1st Oct - excavation
5th Oct - excavation for this part of the channel complete and blinding laid down
5th Oct - sheet piles for entrance being driven
13th Oct - reinforcement mesh for parts of the base slab being laid
15th Oct - some of the concrete bases poured
20th Oct - general shot looking downstream showing one section of wall freshly filled with concrete
20th Oct - general shot looking upstream showing another section of wall just poured
23rd Oct upstream entrance showing the back of the newly installed sheet piles
23rd Oct - part of new left-hand concrete wall complete
29th Oct
29th Oct
3rd November
9th November - Fish Brushes delivered and awaiting installation
12th Nov
30th Nov - flooding stops work
30th Nov - flooding stops work
30th Nov - flooding stops work
7th Dec - floods start to receed
7th Dec. This photo shows the start of the installation of the black recycled plastic panels to protect canoes from damage.
22nd Dec - Works stopped for Christmas
22nd Dec
22nd Dec
22nd Dec
24th Feb - Still waiting for the flood season to end before water is let down the pass. Should be end of March subject to river flows.
24th Feb
24th Feb
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