Annex G Flood Warning Service Information
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Annex G Flood Warning Service Information Annex G1 Environment Agency Flood Warning Codes (extracted from the EA website) http://www.environment-agency.gov.uk/homeandleisure/floods/31620.aspx The Environment Agency warning service has three types of warnings that will help prepare for flooding and take action. They are: • Flood Alert • Flood Warning • Severe Flood Warning [Note: Flood warning and Severe Flood Warning are not specifically applied to groundwater flooding, but these definitions have been included here for completeness as they remain pertinent to areas that suffer both groundwater and fluvial flooding ] Flood Alert What it means: Flooding is possible. Be prepared. When it's used: Two hours to two days in advance of flooding. What to do: Be prepared to act on your flood plan. Prepare a flood kit of essential items. Monitor local water levels and the flood forecast on our website. Flood Warning What it means: Flooding is expected. Immediate action required. When it's used: Half an hour to one day in advance of flooding. What to do: Move family, pets and valuables to a safe place. Turn off gas, electricity and water supplies if safe to do so. Put flood protection equipment in place. Severe Flood Warning What it means: Severe flooding. Danger to life. When it's used: When flooding poses a significant threat to life. What to do: Stay in a safe place with a means of escape. Be ready should you need to evacuate from your home. Co-operate with the emergency services. Call 999 if you are in immediate danger. Warnings no longer in force What it means: No further flooding is currently expected in your area. When it's used: When river or sea conditions begin to return to normal. What to do: Be careful. Flood water may still be around for several days. If you've been flooded, ring your insurance company as soon as possible. Annex G2 Environment Agency Information: regional groundwater levels and conditions G2.1 Water Situation Reports Water situation reports are issued monthly throughout the year both on a national (England and Wales) basis and for all Environment Agency regions (and some Environment Agency Areas). Within Hampshire, water situation reports are provided as follows: • South East Region; o (South East Region); Solent and South Downs Area; o (South East Region); West Thames Area; • South West Region; o (South West Region); Wessex Area. These reports can be found at: http://www.environment- agency.gov.uk/research/library/publications/33995.aspx Extracts from (part of) a water situation report are reproduced below. These reports provide a monthly summary of hydrological conditions and water resources in each Region and Area, including information on rainfall, soil moisture deficit, river flow, groundwater levels and reservoir storage. The reports include maps, graphs and plots and the text and diagrams showing the general groundwater situation and emerging trends and are intended to be relatively easy to understand, even for the lay reader. Groundwater level charts show (for selected and representative monitoring wells across the region) current water level data as well as a range of historically recorded values in bands comprising 7 categories between exceptionally low to exceptionally high (see below for an explanation of these terms). Each monitoring well used to develop the report is shown on a regional map and the (current) water level category colour coded. A typical set of these graphs is also shown below. Some water situation reports (e.g. West Thames Area) also show the dry and flowing lengths of ephemeral (groundwater fed) rivers. Annex G2 Environment Agency Water Situation Report – example extract Summary Page Annex G2 Environment Agency Water Situation Report – example extract Groundwater Information Annex G2 Environment Agency Water Situation Report – example extract Groundwater Information Annex G2 Environment Agency Water Situation Report Categories and Definitions Category Definition Exceptionally high Value likely to fall within this band 5% of the time Notably high Value likely to fall within this band 8% of the time Above normal Value likely to fall within this band 15% of the time Normal Value likely to fall within this band 44% of the time Below normal Value likely to fall within this band 15% of the time Notably low Value likely to fall within this band 8% of the time Exceptionally low Value likely to fall within this band 5% of the time G2.2 Groundwater Briefing Notes In addition to the Water Situation Reports, The Environment Agency also publishes flooding from groundwater “Briefing Notes” which may be issued in certain areas when groundwater levels are high (in excess of seasonal averages). These briefing notes, which are only issued when groundwater levels are rising and have reached a pre determined threshold level (see further below) provide a summary of the current situation, identify where flood alerts are active, provide a qualitative forecast of the risk of flooding and indicate actions being taken and appropriate contacts. The Environment Agency also publish groundwater level information for key boreholes used in the monitoring groundwater flooding (see Figure above). The flooding from groundwater briefing notes and water level monitoring information can be found at: http://www.environment-agency.gov.uk/homeandleisure/floods/137320.aspx and http://www.environment- agency.gov.uk/research/library/publications/99556.aspx An example extract of a “Flooding from groundwater” briefing note for Solent and South Downs area is reproduced herein (included as a separate document, Annex G5) Solent and South Downs Area of the Environment Agency have a developed set of procedures ( Ref 10 ) for groundwater flooding which sets out the actions they will take based on monitoring a set of boreholes across their area (see further below). These procedures are based on national guidance issued internally by the Environment Agency for operating a groundwater flood warning system. Annex G3 Environment Agency Groundwater Flood Warning Service G3.1 Groundwater Flood Alerts The Environment Agency provides groundwater flood alerts through its website and through Flood Warnings Direct (for those who sign up for the service). Currently the Environment Agency issue groundwater flood alerts to 19 areas within Hampshire. These flood alert areas (shown in Annex B Figure 5) have been selected primarily based on the groundwater flooding experienced during 2000/2001 and give good coverage of the areas most at risk from groundwater flooding. Alerts are issued when groundwater levels in a series of monitoring boreholes (or “warning wells”) reach certain pre determined (and regularly reviewed) trigger levels. G3.2 Groundwater Flood Monitoring - Warning Wells Groundwater flooding “warning wells” are monitoring boreholes operated by the Environment Agency to observe the rise and fall of groundwater which include a specific function to monitor the extreme rise of groundwater that may lead to groundwater flooding. A number of these wells are equipped with telemetry (telemetric monitoring boreholes) which allows the water level data to be sent by telecommunication and observed remotely at the Environment Agency Area office. In the procedures followed by the Environment Agency in the monitoring of groundwater flooding warning wells vary between their different regions and areas. In the procedures set out followed by the Environment Agency Solent and South Downs Area, 15 boreholes (11 relevant to Hampshire), equipped with telemetry (i.e. which may be read remotely at the EA office) are identified. There are also supporting “key” boreholes which are used to gather more local supporting information. These are routinely measured monthly and then more frequently in response to triggers set in the telemetry boreholes. Each telemetred borehole and supporting key borehole are used to monitor flood risk in a particular area (known to be at risk from groundwater flooding from historic records). Up to 4 trigger levels may be identified in each borehole with a corresponding set of actions and or consequences (e.g. trigger levels may represent the onset of cellar flooding in some areas). A summary of these warning wells and those in the Wessex and West Thames EA Areas together with the area they cover is given in Table G3.1 below. Procedures in the Wessex Area and West Thames Areas appear less defined, although they also operate similar telemetric monitoring wells. A summary of all the warning wells operated in Hampshire, together with the area they cover is given in Table G3.1 below. Example flood alert messages are shown below. The public may sign up for email communication of groundwater flood alerts through Flood Warnings Direct, and there are direct access phone lines available (see also Table G3.1). Table G3.1 Environment Agency Groundwater Flood Alert Areas and Associated “Warning Wells” GW Current flood Quickdial EA Key Groundwater River Flood alert Environment Agency Groundwater Flood Alert Area Corresponding telemetry well Villages Covered Code Area boreholes Body Catchment Alert area 06/02/12 label Upper Hampshire Pitton, West 1 Salisbury Plain Area 0452 Wessex Lopcombe Corner Hampshire Avon Pitton, Broughton, Nether Wallop, West Tytherley y Tytherley Avon (R.Bourne) West Ashe (Ashe Basingstoke 2 Basingstoke and Sherborne St John 171907 Oakley Loddon Deane, Ashe y Thames Warren) Chalk West Basingstoke 3 Crondall 171908 unknown unknown Loddon Crondall n Thames Chalk West Alton Upper 4 Alton 171909 unknown unknown Wey Alton,