In this section, we provide information and guidance on some of the most frequent issues and misconceptions on flooding.
The causes of flooding
Flooding can be caused by lots of different factors. It could be caused by a burst water pipe, which could flood roads and homes, or through environmental factors, like heavy rainfall events or tidal storm surges.
In Hull, there are many different environmental factors that can cause flooding.
Where flooding can happen
Flooding can happen anywhere. Some areas of Hull are more susceptible to some types of flood risk more than others.
Groundwater flooding
Hull is built on top of a chalk aquifer. Between the chalk and the city are layers of clay. In west Hull, the layers of clay are thinner and so groundwater flooding is more likely to happen in west Hull because it’s easier for the groundwater to find its way up to the surface. Groundwater tends to happen a few days or weeks after a storm or period of heavy rainfall, which can be confusing. This is because the aquifer takes time to fill up and then find its way to the surface.
Surface water flooding
Happens anywhere where water cannot drain away. This could happen when it rains a lot and the sewers become full so there is nowhere for the water to go. Or it could happen on fields that have thin soils that are on top of clay, which water cannot drain through.
River or fluvial flooding
Happens when rivers or watercourses become full and overtop their banks or defences. In Hull there are rivers and watercourses running throughout the city. Hull is shaped like a bowl, so once water is moving outside of the places it’s normally seen, it will flow to the lowest spots following the path of least resistance - this is often roads.
Tidal flooding
This happens in areas along the Humber Estuary. Tidal flooding can happen when stronger winds cause higher than normal waves (a storm surge). As mentioned above, Hull is shaped like a bowl so once water enters the city, it will flow to the lowest spot. This means that areas inland of the estuary are also at risk of tidal flooding.
Sewer flooding
In Hull, the sewers take in wastewater, for example when we flush the toilet or have a shower, and surface water – rain once it falls on the ground. Day-to-day the sewers can manage the flows in them, but during storms or periods of intense or prolonged rainfall, the sewers become full. This causes water to back up on the surface or in people’s homes - toilets and drains.
Reservoir flooding
After the 2007 flooding in Hull, risk management authorities built a series of surface water storage lagoons to the west of Hull. The lagoons catch and store surface water as it comes down the Wolds and slows it down so that it enters Hull’s drainage system when it is not full. The reservoirs are designed to hold a certain amount of water, so if this is exceeded, then areas around the reservoirs would be at risk of flooding.
You can check your long term flood risk to find out what types of flood risk your home or property is at risk from.
Predicting flooding
Flooding is very hard to predict because there are so many factors involved. Each flood event is unique and is caused by a specific set of factors. It is hard to replicate this complexity in models to be able to predict flooding. However, it is possible to predict certain types of flooding when data is available, for example tidal surges or river flooding can be tracked downstream using monitoring equipment. It is much harder to predict and warn people of flooding in areas with little or no monitoring.
Despite the challenges, the Flood Forecasting Centre (FFC) is a working partnership between the MET Office and Environment Agency and they provide services, including -
- data
- forecasts
- information
to support the Environment Agency and Category 1 and 2 responders. The FFC forecast natural forms of flooding including -
- rivers
- surface water
- groundwater
- and the sea