Myth busting

There are many different reasons why an area might flood but in Calderdale, we are particularly at risk. Calderdale’s unique landscape makes it particularly vulnerable to floods. Rainwater runs down the hillsides into the River Calder, causing river levels to rise sharply.
Understanding what makes each type of flood different will help you know what to do to protect yourself, as well as who to contact for assistance.

Calderdale has experienced significant flooding in recent years, prompting a robust and coordinated response to reduce future risk and build long-term resilience. Local authorities, community groups, and national agencies have come together to deliver a wide-ranging programme of flood prevention and preparedness.
Here are some of the major accomplishments and ongoing efforts aimed at protecting people, homes, businesses and infrastructure across the borough:

• £133 million secured to fund work across the key themes of strengthening defences, natural flood management, resilient infrastructure, and community resilience.
• Significant progress on flood alleviation schemes across the borough. By 2027, seven schemes in Calderdale will protect over 1,390 properties.
• More than 120 sites in the borough have been used for natural flood management (NFM) since 2016, involving over ten delivery partners, hundreds of volunteers, and multiple funding streams.
• Opening of a new Flood Information Centre in Hebden Bridge to keep the community updated on progress in reducing the risk of flooding in the town.

In Calderdale dredging the rivers would not be the most efficient or sustainable way of reducing flood risk and may actually increase flood risk to downstream communities. Natural processes in many rivers means silt will return and accumulate in the same places very quickly, sometimes only weeks after dredging is carried out, therefore any increase in channel capacity will be short-lived. The Environment Agency consider each location carefully and dredge where they know it will make a difference to reduce flood risk. Dredging and desilting can have serious and long-lasting negative impacts on the environment. For example, it can damage or destroy fish spawning grounds and make riverbanks unstable. Silt can become suspended in the water, lowering oxygen levels, potentially releasing harmful chemicals that may be present. Instead, a combination of natural flood management and improved flood defences offers a more effective, long-term approach to mitigating flood risks while protecting the community and environment.

Beavers thrive in flat, lowland floodplains with slow-moving rivers and extensive wetlands. The Calder Valley, by contrast, is made up of steep-sided valleys and fast-flowing watercourses, which are not ideal for beaver activity. The rivers in Calderdale have been heavily modified over centuries - think weirs, mill ponds, sluices, and river walls. Beavers don’t distinguish between natural and engineered structures, so their dam-building could interfere with existing flood defences and infrastructure. In high-energy rivers like those in the Calder Valley, beaver dams could break apart during extreme rainfall, sending debris downstream. This could block bridges, culverts, or trash screens, potentially worsening flood risks rather than reducing them.

While it might seem like the Council isn’t doing enough, the reality is more complex. Highway drainage needs routine maintenance. There are 40,000 gullies across Calderdale. These are emptied and cleaned as part of a yearly maintenance programme.
It is possible for drainage systems to become blocked even with regular maintenance:
- Heavy rainfall can overload a system.
- Mud and leaves can cause blockages.
- Covers can become damaged.
The Council also respond to reports of blocked drains, especially if flooding is likely. And in some areas, natural flood management and infrastructure upgrades are being used to reduce pressure on drainage systems.

Flooding can come from a variety of sources—not just rivers or the sea. Here are some common types you should be aware of:
- Flash or Localised Flooding
Flash floods occur when an intense amount of rain falls in a short period. Drainage systems and sewers can quickly become overwhelmed, causing water to overflow and flood streets or properties.
- Sewer Flooding
When foul sewers overflow, the floodwater is often contaminated with sewage. In severe cases, this contaminated water can back up through the sewer system and flood the inside of buildings.
- Surface and Highway Flooding
Roads and pavements are typically drained by highway drains or roadside ditches, especially in rural areas. During heavy or prolonged rainfall, these systems can struggle to cope, leading to surface water flooding.
- Reservoir Flooding
Reservoirs store large volumes of water behind dams. While dam failures are extremely rare due to strict safety standards, a breach could release a significant amount of water very quickly, causing severe flooding downstream.

Just because an area hasn’t flooded before doesn’t mean it won’t flood in the future. Many areas in the UK experienced flooding for the first time in recent years due to prolonged rain, unexpected flash floods or overwhelmed drainage systems - even though they had no prior flood history.

Sandbags are often not effective because water can seep through them, and finer materials like clay can leak out. They are also not reusable, can rot in storage, and are rarely the best solution for keeping floodwater out. There are more effective, easier-to-use, and reusable alternatives available.

Insurers do not guarantee to provide cover in all circumstances and some insurers may consider your risk to be unacceptable to them. Areas at risk of flooding may have higher premiums and excesses (the amount you must pay towards the costs of repair) to reflect that risk. The cost and availability of insurance may even vary within individual streets as different insurers will want to limit their exposure to claims from any one event. Flood RE is a re-insurance Scheme that makes flood cover more widely available and affordable as part of your home insurance.

Flood water is often contaminated, fast-moving, and unpredictable, making it a danger to health and safety. Here’s why flood water is dangerous:
Contamination: Flood water can contain:
• Sewage
• Chemicals from homes, farms, or industrial sites
• Debris like glass, metal, or sharp objects
• Dead animals or waste
• Exposure can lead to infections, skin rashes, or serious illnesses like leptospirosis or gastrointestinal diseases.
You can’t see what’s beneath the surface. There may be:
• Open manholes
• Sharp debris
• Uneven ground or sinkholes
• Electrical hazards from submerged power sources
Even shallow flood water can knock you off your feet. Just 15 cm (6 inches) of fast-moving water can sweep an adult away, and 30 cm (1 foot) can move a car. Flooding can weaken roads, bridges, and buildings, making them unsafe to walk or drive on, even if they appear intact.

There’s a lot you can do to reduce the risk of flood damage to your property. Even if you haven't flooded before it's worth being prepared just in case the worst should happen. There are some simple measures that you can take – and products you can buy – that can protect your property and limit damage during a flood. This could save you money and heartache, as well as allowing you to return to your property much sooner.

Since 2023, over £180 million has been invested to deliver major improvements and reduce discharges from storm overflows across Yorkshire. This work includes:
• Construction of new surface water sewers
• Installation of underground storage tanks
• Implementation of nature-based solutions and sustainable drainage systems (SuDS)
These Yorkshire Water initiatives are designed to support the region’s sewer network and improve the treatment of wastewater for 5.5 million customers. As a result, overall storm overflow discharges were reduced in 2024.

(Source: Yorkshire Water)

While new development sites have the potential to increase flood risk, the Council, as the Lead Local Flood Authority (LLFA), checks minor and major planning applications to prevent this. They ensure that new developments don't increase surface water flow rates beyond existing levels and that proper drainage and maintenance plans are in place. This is done according to national and local planning policies to make sure flood risk isn't increased elsewhere.

It’s a common belief that flood alerts should always be spot-on, but the reality is more complex. The predictions you see come directly from computer models. These models use real-time rainfall and river level data, combined with weather forecasts. However, they aren’t adjusted by a human forecaster, which means they can sometimes miss the mark, especially in smaller catchments like those in Calderdale, where even slight changes in rainfall can make a big difference.

In contrast, flood warnings issued by the Environment Agency are refined by trained flood forecasters. These experts interpret the models, understand the local landscape, and use real-time data to make informed decisions. That’s why you might see a difference between the forecasted river levels online and those included in official flood warnings.

In England, the Environment Agency provides 3 types of flood warning:

• Flood alert – flooding is possible
• Flood warning – flooding is expected
• Severe flood warning – flooding could be a risk to life and significant disruption to communities

Severe flood warnings can be issued before, during or after flooding.

You should take flood warnings very seriously. The action you need to take is different for each type.