Guernsey Water has completed a significant project to replace the two sea outfalls that link to the Belle Greve Wastewater Centre (BGWwC). Work took place between April and October 2015 with contractors Van Oord UK Ltd and Geomarine.
An overview of the sea outfall renewal project
An overview of Guernsey Water's sea outfall renewal, the final phase of the island's wastewater centre project.
An overview of the final phase of Guernsey's wastewater infrastructure project
Mark Walker, Guernsey Water's Capital Delivery Manager, gives an overview of the onshore and offshore construction work which marks the final phase of upgrades to the island’s wastewater infrastructure.
Areas of work
Guernsey Water (GW) is replacing the two sea outfalls through which the Island’s wastewater is discharged into the Little Russel. These are the Long Sea Outfall ( LSO - the normal outfall through which the majority of flows discharge) and the Short Sea Outfall ( SSO - the outfall only used when the LSO is overloaded and the storm tank is full i.e. during heavy storm conditions).
There will be two separate areas of work - one is the on-land work which will involve laying two new pipes connecting the Belle Greve Wastewater Centre (BGWwC) to the new outfalls. This will involve the removal of parking along the BGWwC access road for a period of about 3 months. As the pipes will be installed across Les Banques, the road will be under temporary traffic lights from 24th August to 11th September 2015 . Further information regarding traffic management can be found at www.iris.gov.gg .
GW will also be constructing a chamber adjacent to the slipway to Belle Greve Bay, which is where the pipes from the BGWwC will connect to the outfalls. This section of work will be carried out by Geomarine, and is shown on the plan below :
The other part of the works will be the marine works, which will involve dredging the seabed with a barge-mounted excavator, before lengths of pipe are shipped in from Norway. There will then be a controlled sink of the pipes into position before the excavations are backfilled. This section of work will be carried out by Van Oord UK Ltd (as main contractor for the whole project), and is shown on the plan below.
We recognise that parts of this project will have a significant impact on properties in the area. We have liaised with all interested/affected parties in order to try and minimise the inconvenience wherever possible.
A survey of the outfalls in 2011 showed that the LSO was in a bad state of repair and could suffer catastrophic failure at any time, while the SSO was over a century old and in need of quick replacement. This project not only mitigates a potential failure, but has also recognised that the new pipes will be lengthened so that wastewater will be discharged into deeper and faster-flowing sections of the Little Russel.
This project will allow us to meet the long-term needs that will be required under future water quality legislation, at a lower cost than would be achievable if the works were undertaken retrospectively at a future date. It is also important to consider that the outfalls should have a lifespan of around 70 years, so it is vital that we make sure this investment creates a design that meet our needs now and in the future.
Transportation of outfall pipes from Norway
The nine outfall replacement pipes (eight of which are nearly 500m long) are slowly being towed from Norway to Guernsey and are expected to arrive early afternoon on Monday 25 May.