WAT/Specific/TBT-WAT-010

Flood Risk and Rising Water Levels

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Construction sites near rivers, coasts, and floodplains face risk from rising water levels and flash flooding.
Water levels can rise rapidly from upstream rainfall, tidal surges, or dam and reservoir releases.
Excavations flood first; workers in trenches can be trapped and drowned as water rises around them.
Plant and equipment in flood zones are damaged, displaced, and can create downstream obstructions.
Flood water carries debris, chemicals, sewage, and sediment that create contamination and health hazards.
Environment Agency flood warnings provide advance notice: flood alert, flood warning, and severe flood warning.
A site-specific flood risk assessment should identify trigger levels for protective action and evacuation.
Temporary flood barriers, pumps, and sandbags should be pre-positioned where flooding is foreseeable.
Access routes to and from the site may become impassable during flood events, trapping workers on site.
CDM 2015 requires that foreseeable flood risks are assessed and planned for before construction begins.

Drowning	Workers drown in flooded excavations and are swept away by flash flooding on construction sites near water.
Rapid escalation	Water levels rise in minutes during intense rainfall or tidal events, leaving no time for unprepared evacuation.
Contamination	Flood water contaminates the site with sewage, chemicals, and debris, creating health hazards for returning workers.

Don't

Register for Environment Agency flood warnings for the site location.
Prepare a site-specific flood risk assessment with trigger levels for action.
Pre-position flood barriers, pumps, and sandbags where flooding is foreseeable.
Evacuate excavations immediately when flood warnings are issued for the area.
Monitor river levels and tidal forecasts daily during work near watercourses.
Identify evacuation routes that remain passable during flood events.
Secure plant, fuel, and chemicals above anticipated flood levels before events.
Brief the team on flood triggers, evacuation routes, and assembly points.
Inspect the site for contamination and structural damage before re-entering after flooding.
Keep emergency contact numbers for the Environment Agency available on site.

DON'T work in excavations during active flood warnings for the site location.
DON'T ignore rising water levels or assume they will recede before reaching you.
DON'T drive vehicles through flood water of unknown depth on or off site.
DON'T store fuel, chemicals, or skips in areas at risk of inundation.
DON'T wait for the flood to arrive before starting protective actions.
DON'T re-enter the site after flooding without checking for structural damage.
DON'T assume flood warnings only apply in winter; summer flash floods occur too.
DON'T leave plant in flood zones where it could be swept into watercourses.
DON'T block or obstruct natural drainage channels that may carry flood water.
DON'T delay evacuation because you want to finish the task first.

See also: Flood and Extreme Weather Response | Working Near Open Water

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