Careful planning to replace water main at Moulin Huet
GUERNSEY Water has been carefully planning how to replace a raw water main, which runs through an important woodland site.
The water main going through woodland on the north-west of the Moulin Huet valley, has been suffering an increasing number of bursts as it reaches the end of its life. But replacing it is not straightforward, as it runs through a site of special significance.
Guernsey Water has applied for permission to replace the existing 200mm diameter UPVC raw water main between the Moulin Huet raw water pumping station and Rue Jacques Guille.
In the application project engineer Dale Overbury said the utility was planning to undertake a four-week programme within the area in August and September.
‘These dates have been proposed to reduce any disturbance to bird breeding within the local area,’ he said.
‘These dates should also mean that ground water levels are low and therefore reduce the likelihood of working within waterlogged conditions. With the land parcel being a woodland site, avoidance of trees and their root systems have been taken into consideration.
'It’s proposed that no large established trees will be removed, however younger areas of vegetation growth will be removed to allow light through the woodland canopy.’
A trench, which will be 60cm wide and a metre deep, will be dug to remove the existing pipe and replace it with a 300mm ductile iron pipe.
The pipe’s route will avoid most of the tree roots, but seven trees are likely to be affected. Guernsey Water plans to check them a year after the work is finished.
The woodland is currently managed by States Agriculture, Countryside & Land Management Services and borders a stream which runs beside the road down to the beach’s car park.
Mr Overbury said the work was important.
‘The Moulin Huet catchment is an important part of the island’s integrated southern raw water collection system,’ he said.
‘It captures raw water from approximately 2% of the island’s stream catchment, transferring that to St Saviour’s raw water storage reservoir where, once treated, it serves approximately 10,200 island homes.’
Guernsey has less than 8% woodland cover, compared with 12% of the UK and 42% of Europe.
An Environment Guernsey ecology assessment, which was included with the application, noted the area was an important woodland habitat, with a range of trees and invertebrates, while the freshwater stream was known to support the European eel – a critically endangered species.
‘The installation of the new water main, which requires trenching through the woodland area, could cause significant damage to the site, potentially lasting for a number of years thereafter,’ its assessment said.
‘To keep impacts to a minimum, it is critical that the works adhere to the mitigation measures. In particular, the trenching should be undertaken in late summer or early autumn and follow a route, which avoids the need for extensive felling or trees or causes damage to root systems.’
It stated that with mitigation, the site should recover within three years.
n The plans can be viewed at https://www.gov.gg/liveplanningapplications.
