Guernsey Water develops long-term strategy to manage flooding

Guernsey Water has launched a long term plan to reduce the risk of sewer flooding and pollution by effectively tackling storm water across the island.

The Surface Water Management Policy (SWMP), endorsed by the Committee for the Environment and Infrastructure, is part of Guernsey Water’s integrated drainage strategy to deliver effective drainage as set out in its 10-year business plan launched in 2016.

Guernsey Water operations manager, Jon Holt, said:  “Decades of development have reduced our green spaces so there are fewer places for the rain water to drain naturally.  When a lot of rain falls in a short space of time our drains quickly become overwhelmed and the only route is overland often causing flooding. We have particularly seen the impact of this in St Peter Port over recent years.”

Initiatives to improve the management of surface water in Guernsey have included extending the drains at Vauvert, building large underground storm tanks in  a field next to the Belle Greve Wastewater Centre and installing a computerised system (known as SCADA) to remotely monitor and control the island’s pumping stations.

Guernsey Water has also developed a hydraulic model of the sewerage system which predicts the impact of heavy rainfall and assesses the best way to handle the excess surface water without causing flooding. The long term aim is to actually reduce sewer flooding and instead manage the intensity of surface water across the island in a sustainable way.

As part of the SWMP, Sustainable Urban Drainage Systems also known as SuDs will be introduced where opportunities are found to ease the impact of urban creep and climate change; urban creep is when property extensions and paved driveways increases the speed of runoff into the sewers during heavy rainfall.

SuDS aim to mimic natural water management principles; it’s designed to drain surface water into the ground rather than the conventional practice of routing run-off water through a pipe to a watercourse or sewer which reduces the pipe or sewer’s capacity.

Permeable surfaces (where water naturally soaks into the ground) are one type of SuDS which are being actively encouraged; particularly within urban areas. 

A strategy will now be developed to gather information and set targets to better manage surface water across the island from impermeable surfaces (those that do not absorb water) connected to the foul water system. It will then identify and prioritise areas in the island where SuDS would be of greatest benefit.

“Successful sustainable drainage relies on integration from a number of key sectors including the construction industry, planners, architects, business and home owners and States departments,” said Guernsey Water’s general manager, Stephen Langlois.

“Although the SWMP is not going to be a quick fix it is an opportunity to educate, communicate and encourage sustainable values.

“Our key aim is to deliver more effective drainage methods and ultimately protect the island’s environment by reducing the risk of sewer flooding and pollution.”

A full copy of Guernsey Water’s SWMP can be found here:  http://bit.ly/2mLxWkg