Construction of Fish Passage Weirs

This project was to replace an existing weir with three lower weirs to enable fish passage further up the river. Restoration works to re-model the river channel and improve fishery habitat were then carried out downstream of the new weirs.

The designed water level in this impounded stretch of the Little Stour was very important for both farm land irrigation and historical aesthetics. Therefore the new weirs were designed to maintain this water level yet reduce the height and enable fish passage over them by means of a central notch.

The access to the working area was through nearbye old gravel pits that were now a fishing club and then several hundred metres up the river bank to get to the existing weir which was quite remote.

The setting out of the new weirs was carried out and then the sheet piles were driven to form their structure using a long reach excavator fitted with a piling hammer.

A temporary diversion channel was then excavated and a temporary sand bag dam installed across the river to divert the flow around the location of the new weirs.

The sheet piles were then clad in recycled plastic and stone was imported and placed as rock armour to protect the banks of the weir pools.

The old weir was then carefully removed and more stone placed upstream of the new weirs to increase the velocity of the river on the approach to the new weirs and prevent silt building up above them as had happened with the old weir.

River restoration works were then carried out downstream of the new weirs for several hundred metres to create meanders, pools and riffles improving the fishery habitat.

The temporary dam was removed and the weirs commissioned. The temporary diversion channel could then be filled in and the working area tided and seeded with grass.

Construction of Flood Embankment

This project was to construct a new flood embankment to protect domestic properties and an electrical sub station adjacent to the River Roding.

The line of the embankment was set out and the topsoil stripped and set to one side. The clay based material was imported and keyed into the existing ground and then compacted in layers using the tracked excavator and vibrating sheeps foot rollers.

A Thames water storm water manhole was located within the line of the new embankment and so this was raised as part of the works along with a headwall and flap valve at the termination of the embankment at the river to drain any water accumulated on the back slope.

Once the structure was completed it was covered with imported topsoil and seeded with grass.

Warning markers identifying the structure as a flood embankment were also set in concrete along the top of the embankment.

Weir Removal and Bridge Revetment Construction

This project was to break out an existing weir structure enabling migratory fish passage further up the river, re-model the bed of the river to suit the lowered water level and construct new revetments to protect the bridge immediately upstream of where the weir was.

Once measures to capture disturbed sediments were put in place downstream the weir was broken out and removed using a long reach excavator working from the bank above.

The bed downstream of the weir was then re-graded to suit the lower water level.

The banks and bed of the river under the bridge were carefully excavated to accommodate the gabion basket revetment.

A temporary dam was installed to divert the water down one half of the channel leaving the other half to be worked on. Diesel pumps were used to remove seepage into the working area through the dam.

Stone filled mattresses were installed across half of the bed of the channel to act as a footing to the new revetment and prevent scour underneath the bridge.

The stone filled gabion baskets were then installed above the reno mattresses in tiers taking the revetment up to ground level.

The temporary dam was then moved diverting the water down the completed half while the remainder was completed tying the reno mattresses to those previously installed on the first half to create one secure joined up footing and then carefully excavating the bank and installing the baskets above again as before.

The banks were narrowed above and below the bridge and gravels were imported to form two riffles, one upstream of the bridge and one where the weir was.

Re-lining of Large Pond

This project was to re-line a leaking pond at the foot of the south downs. The original liner had been poorly installed with no protective felt underlay and was leaking possibly due to the fact that every winter for some years the ground water rising from the chalk below lifted it to the surface of the pond for weeks until the springs subsided.

The old liner was removed and the pond deepened slightly and re-modeled to include planting areas in the margins then prepared for the new liner with an anchor trench dug around the perimeter to secure the felt and liner within.

Prior to installing the liner a land drain was installed from the centre of the pond falling to a point outside the curtilage of the pond adjacent to the existing outlet/overflow channel.

Once clear of the pond a 90 degree bend was attached and a riser bringing it to ground level. Now, during periods of excessive ground water a submersible pump could be lowered into the land drain to remove the water and prevent the liner from lifting and damaging itself.

Withe the land drain installed the new felt underlay and liner could be laid out and the works completed including creating marginal planting areas in the corners.

A new pumping system was also set up to circulate and aerate the water around the two ponds.