What is flooding from heavy rain and groundwater?
Flooding from heavy rain and groundwater (Dutch: wateroverlast) is nuisance or damage caused by too much water temporarily standing on the street, in the garden or inside a building. It usually comes from intense rainfall, sewer backflow or a high water table. A river bursting its banks or a breached sea defence is a different and much larger-scale problem.
Causes
- Intense rainfall: during a short, heavy downpour the drains cannot carry water away fast enough. It flows in over thresholds, through air bricks and lightwells.
- Hard surfaces: paved gardens and streets stop water soaking in, so it runs to the lowest point.
- High groundwater: wet basements and crawl spaces, especially in winter or after long wet spells.
- Sewer backflow: when a combined sewer is overloaded, water can rise back up through floor drains and toilets in low rooms.
Insurance
Check your home insurance for cover of flood, storm water and sewer backflow, and for any conditions such as a working non-return valve. Cover varies between countries and policies.
Measures for house and garden
- Slope ground away from the house so water runs off.
- Remove paving and replace it with planting, gravel or permeable paving.
- Hold rainwater back: water butt, cistern, soakaway or rain garden, where permitted.
- Fit a non-return valve in drains from basements and other rooms below street level.
- Raise the entry points: thresholds, lightwells and air bricks set above street level, or fitted with flood covers.
- Basement: a sump with a submersible pump and proper waterproofing limit damage.
Related terms
- Rainwater drainage
- Stormwater retention
- Cistern
- Groundwater level
- Groundwater seepage
- Waterproofing
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