Amenity Water Management Ltd
  info@amenitywater.co.uk
  01798 831624

Amenity Water Limited Logo

Dredging of On-Line Lake

This project was to dredge the accumulated sediment from an on-line lake. On-line meaning a watercourse normally flows through it and on this occasion several ground water springs rose into it. This meant alot of pumping was required to divert and remove as much water as possible to facilitate removal of the silt!

  • Thorncombe Park 2007 002
    The lake is slowly drained revealing the silt.
  • Thorncombe Park 2007 009
    The dull extent of the silt.
  • Thorncombe Park 2007 029
    Rubble is imported to form a temporary access ramp into the lake for the excavators.
  • Thorncombe Park 2007 009
    Some of the pumps set up on the dam.
  • Thorncombe Park 2007 071 2
    The silt is loaded into dumpers to be tipped and spread on adjacent farm land.
  • Thorncombe Park 2007 117
    The fiddly bit under the bridge.
  • Thorncombe Park 2007 097 2
    The lake with the dredging almost complete.
  • Thorncombe Park 2007 002
  • Thorncombe Park 2007 009
  • Thorncombe Park 2007 029
  • Thorncombe Park 2007 009
  • Thorncombe Park 2007 071 2
  • Thorncombe Park 2007 117
  • Thorncombe Park 2007 097 2

The upstream inlet of the watercourse into the lake was temporarily dammed and a pump set up to over pump this water down the length of the lake and into the lake below.

Silt control measures were put in place downstream and the sluice was then opened on the dam and the lake slowly drained to reveal the extent of the silt present.

A temporary access ramp formed with brick rubble was formed at the downstream end of the lake which was the only possible access in off the dam.

The dredging works commenced with the silt loaded into wheeled dumpers to be spread on adjacent farmland for soil improvement.

Additional pumps were set up on the dam to deal with the multiple springs rising into the lake which were diverted to the pumps as the dredging progressed.

At the peak of the works there were 6 diesel pumps running 24 hours to control the water entering this lake. Even with this pumping the water and the silt were sufficiently in contact to mean that we were moving watery silt like ʻsoupʼ which is a much slower process than moving ʻdrierʼ in situ silt which has no contact with water during the works. However we got there in the end!

Once the dredging works were complete we carried out some repair works to the banks and the island using hazel faggot bundles and pre-established coir rolls to provide a new sustainable revetment.

Flood Defence Outfall Refurbishment

This project was to re-furbish an outfall on the River Stour and improve the access arrangements to it for future maintenance.

  • Img 1202
    The long reach excavator is delivered to the narrow lane leading to the site.
  • Img 1220
    With the pumping chamber beneath sufficiently protected the excavator is positioned in place behind the flood wall.
  • Img 1215
    This enables it to reach sufficiently into the river to construct the temporary dam and work on the outfall.
  • Dscn1373
    With the temporary dam in place the formwork is constructed and reinforcing installed ready for the new concrete.
  • Dscn1384
    The new concrete frontage of the outfall taken from below water level!
  • Dscn1408
    The bin store with gate leading to the steps over the flood wall.
  • Dscn1404
    The refurbished outfall looking downstream showing the lower steps and new fencing.
  • Img 1202
  • Img 1220
  • Img 1215
  • Dscn1373
  • Dscn1384
  • Dscn1408
  • Dscn1404

The structure of the existing outfall had been compromised through age and freeze thaw weathering and so a new layer of reinforced concrete was to be cast over the existing structure.

Two new sets of steps were incorporated into the design to enable safer access to the outfall for future maintenance and the residents of the adjacent houses were to be provided with a new fenced area to store their bins.

The access was very tight down a narrow cul de sac lane to some houses. A long reach excavator was required to reach over the flood defence wall and work on the structure. In order to carry out the works this machine had to sit on the pumping chamber that fed the outfall and so a temporary works to design protect the chamber and spread the load of the machine was devised.

A temporary dam was installed in the river to keep the working area dry and a pump was set up to deal with the seepage through it.

The pipes from the pumping chamber that discharge onto the outfall were extended over the temporary dam to keep the working area dry in case of rain during the construction works.

The existing structure was cleaned and prepared to receive the new concrete before the reinforcing was installed.

The formwork was constructed around the existing structure and the new concrete was poured.

Once the concrete had cured sufficiently the formwork and temporary dam could be removed.

The two sets of steps were then installed, the new bin store was constructed and some other fencing to deter public access was erected.

Hard revetment works to prevent erosion in a river channel

This project was to bolster the existing erosion control measures downstream of the major weir structure controlling flow from the River Thames down the Jubilee River.

  • IMG 0725
    The erosion on the left bank at the downstream extent of the existing rock armour.
  • IMG 0720
    The erosion on the right bank downstream of the gabion baskets.
  • IMG 0905
    The 8t tracked excavator is craned onto the pontoon.
  • IMG 0954
    The long reach excavator loads the pontoon with rock.
  • DSCN1310
    The new cleaner rock in position on the left bank.
  • DSCN1308
    The toe piles to hold the new blocks in place are driven on the right bank.
  • DSCN1328
    Imported ballast is used to fill the eroded areas and form a level slope. The blocks are then laid on the geotextile fabric.
  • DSCN1338
    The completed armorloc revetment prior to being blinded with ballast to ʻlock the blocksʼ.
  • IMG 0725
  • IMG 0720
  • IMG 0905
  • IMG 0954
  • DSCN1310
  • DSCN1308
  • DSCN1328
  • DSCN1338

The Jubilee river was constructed in the later part of the 1990ʼs as part of a flood alleviation scheme for Eton, Windsor and Maidenhead. Since it was commissioned it has been tested a few times with major flood events and required some ongoing maintenance to the banks immediately downstream of the tilting weirs.

On the left bank we were to add to the existing rip rap(rock armour) protection at the downstream extent where the flows had found a weak spot and the bank was eroding.

This work was carried out using a modular floating pontoon to transport the rock across the river from the site compound above the right bank to the left bank. The rock was loaded onto the pontoon using a long reach excavator and then placed by a smaller 8 tonne machine located on the pontoon.

The pontoon sections were craned in from the bridge above and assembled in the channel before 8 tonne excavator was craned down onto it. Timber bogmats were then placed over the pontoon to protect the decks. The pontoon is manoeuvred into position using a work boat.

On completion of the rock placement works began on the right bank where the existing interlocking concrete block revetment required extending up the bank adjacent to some existing stone filled gabion baskets where the water in high flows had found another weak spot.

It was not possible to link the new concrete blocks to the existing ones and so a row of interlocking trench sheets was driven along the top edge of the existing ones to act as a toe (base) for the new blocks and prevent them moving.

The gap between the two sets of blocks was filled with mass concrete. Ballast was then imported to fill the eroded area and form a level surface to lay the new blocks on.

Once laid the new interlocking armorloc blocks are blinded with ballast to lock them together in place.

Sheet piling repair to remote island

This project was to repair a failed section of sheet pile revetment on a remote island between two weirs on the upper River Lea in Hertfordshire at a place called Amwell Magna, the oldest fly fishery in the UK!

  • IMG 0826
    The island looking upstream.
  • IMG 0828
    The failed revetment close up.
  • IMG 0870
    The floating pontoon looking downstream.
  • IMG 0875
    The spider crane and hammer driving the last few piles.
  • IMG 0826
  • IMG 0828
  • IMG 0870
  • IMG 0875

Due to extremely poor access an innovative approach had to be sought to prevent major enabling works being required to the surrounding countryside in order to bring in conventional large items of plant to carry out the work. The only access was down a narrow track suitable for a transit sized vehicle.

A jetfloat modular plastic pontoon was mobilised to site and assembled in the river to form a floating access track to the island that was approximately 4 metres wide and 20 metres long, filling the river immediately upstream of the island with an access ramp down onto it from the bank.

An upper deck was then constructed above the jet floats using steel framework and heavy duty plastic mats in order to strengthen it and take the loading that would be produced from the crane.

A spider crane and compressed air driven piling hammer were then mobilised to site and set up on the pontoon.

The piles were driven to plug the gap and the void behind was then filled with imported crushed stone before a concrete slab was poured on top to match the existing.

The area behind was the dressed with imported topsoil and seeded with grass.