Flood Guide Rainfall and River Flooding
Most of the rainfall over the British Isles is brought by weather fronts associated with low pressure systems in the atmosphere and varies considerably by region. Fortunately, most of the rainfall finds its way to the sea via the streams and rivers which form the natural drainage system but in very heavy rainfall events the natural and man-made drainage systems can be overwhelmed.
Also, some of the rainfall occurs in showers from large convective cloud (cumulonimbus) and very heavy showers, often accompanied by hail and thunder, can produce localised downpours, sometimes causing flash floods. Heavy rainfall over high ground can cause river levels to rise quickly downstream in places which have remained dry.
Tidal flooding and storm surges
Sea water level around the coast is influenced by both tides and weather conditions. Whereas the tides are predictable for quite long periods ahead, the effect of weather is only predictable for a few days or sometimes hours ahead. At any time, both the tidal and weather components contribute to the sea water level at any place.
Areas of low atmospheric pressure can both raise sea level and generate strong winds. The combined effect of low air pressure and strong wind is known as ‘storm surge’.
If a storm surge occurs on top of a large spring tide, some coastal areas can be susceptible to flooding and in locations exposed to strong onshore winds, waves and swell can exacerbate coastal flooding problems.
Maps showing areas at risk from flooding and regularly updated flood warnings for the UK are provided by the Environment Agency at: https://www.gov.uk/government/organisations/environment-agency
Weather forecasts and warnings are provided by the Met Office at: http://www.metoffice.gov.uk
Regularly updated flood warnings and maps showing areas at risk of flooding for the Isle of Man are provided by the Department of Infrastructure at: http://www.gov.im/transport/floodwatch
General advice on preparation for a risk of flooding and getting help during and after a flood event is available from the Environment Agency at: https://www.gov.uk/prepare-for-a-flood/ find-out-if-youre-at-risk
If your property is located in an area at risk from flooding, EnviroSystems will be happy to provide advice on the best strategy to mitigate the risk of damage
Remember that, when flooding occurs, if you are in danger or you see someone else in danger, don’t hesitate to dial 999.
Ronaldsway Met Office, part of the Department of Infrastructure, has developed systems to monitor and predict both coastal and rainfall flood risk. Warnings are provided through a FloodWatch section of the Government website and through other media such as forecasts on Manx Radio.
The FloodWatch web pages provide information on the imminent risk of flooding and also contain ‘area at risk’ maps for planning developments. There are also useful sections containing information about how to prepare for a flooding event and about where you can obtain help and advice to mitigate the effects of flooding.