Tuesday 10 February 2015
Guernsey Press Enquiry:
In regard to our conversation, can the department please answer the following. For reference, this article will help provide context\:
http://www.telegraph.co.uk/news/weather/11370901/Britain-braced-for-floods-as-supertide-strikes.html
- Is the department actively planning to take any measures to protect the island from these so-called 'supertides'?
- If so, what are they, how much do they cost?
- If not, why not?
- Will the department be liaising with property and business owners to advise them what to do? What advice will it be giving out? If not, why not?
- Does the department believe the island is at any increased risk of flooding and where is it getting its advice from?
Please add any commentary the department wishes to. While this is not planned in for tomorrow, a response today would be appreciated.
Environment Department Response:
The Environment Department has been aware of the increasing number of high tides of 10m or more predicted for Guernsey. In 2014 there were 9 tides predicted at 10m or more. In 2015 there are 24 such high tides, with the highest tides of 10.3m on 21st February, 22nd March and 29th September. Barometric pressure also affects the height of the tide, if the pressure is low the tide will be higher. Wind speed and direction is also a prime factor on how such tides will affect the island's coasts.
The details of all high spring tides are noted by the Department's staff as soon as tide tables are issued each year. The staff also monitor the daily Guernsey Meteorological office five-day weather forecasts together with national and worldwide weather events.
Although there is a greater number of tides this year they are not predicted to be exceptionally higher than is common on a high spring tide in the Channel Islands and as is usual the storm boards are put out across slipways before all high spring tides and checked each day. There is no additional cost involved.
Severe storms combined with high tides, such as experienced last March, will inevitably cause overtopping of waves over sea walls and storm boards and this may cause some coastal flooding. Many residents along Guernsey's coast roads maintain sandbags or boards to prevent seawater coming into their front gardens or homes during the highest tides. People living along the east and west coasts are well used to the challenges that can arise during these high tides but the period of overtopping and any associated flooding is usually relatively short and confined to the period immediately before and after a high tide.
Much greater risk is presented when very high tides coincide with periods of heavy rain. Rivers already swollen with run-off from the surrounding countryside will meet the surge from the high tide, forcing the water up stream. This can result in large areas of land being very suddenly inundated by vast volumes of sea and river water to a considerable depth. Such floods can affect communities some distance inland who may suffer severe flooding with very little warning. This type of flooding is not relevant to Guernsey's situation.
It is anticipated that rising sea levels will set greater challenges for Guernsey in the future. The States of Guernsey approved the Environment Department's coastal flood plans to mitigate the risk of flooding through predicted rising sea levels and work is underway to identify defences for prioritised coastal areas as agreed by the States in 2013.
Contact Information:
Environmental Services Unit
Environment Department
Tel: 717200
