Heavy rainfall puts drainage systems under considerably more pressure than normal day-to-day use.

When a large amount of water enters the drainage network within a short period of time, problems that have previously gone unnoticed can suddenly become much more obvious. Outside drains may begin to overflow, water can collect around gullies and inspection chambers can fill more quickly than usual.

Sometimes this is simply the result of an unusually high volume of rainfall. In other cases, heavy rain can expose a partial blockage, damaged pipe or another underlying drainage problem.

So, how can you tell the difference?

In this guide, we'll look at how heavy rain affects your drains, the warning signs worth paying attention to and when it may be time to have the drainage system professionally investigated.

Why Can Heavy Rain Cause Drainage Problems?

Drainage systems are designed to carry water safely away from our homes and businesses.

During prolonged or particularly intense rainfall, however, considerably more water may enter drains and sewers within a short period of time.

Surface water runs from roofs, driveways, roads and other hard surfaces, while the surrounding ground can eventually become saturated and absorb less rainfall.

The drainage network therefore has much more water to deal with than during normal conditions.

A healthy drainage system should generally cope with everyday rainfall, but periods of unusually heavy rain can expose restrictions, damage and other problems that weren't obvious during drier weather.

Why Does My Outside Drain Overflow When It Rains?

An overflowing outside drain doesn't automatically mean there's a serious problem with the pipe itself.

The first thing to consider is whether the drain only struggles during exceptionally heavy rainfall or whether the problem also occurs during normal conditions.

If water drains away again once the rainfall eases, the drainage system may simply have been dealing with a temporarily high volume of water.

If the water remains, repeatedly backs up or the drain also struggles during dry weather, there could be an obstruction restricting the flow.

Leaves, silt, grease and other debris can reduce the capacity of a drain long before it becomes completely blocked.

When heavy rain arrives, that reduced capacity suddenly becomes much more noticeable.

Our guide to what causes blocked drains explains some of the common reasons these restrictions develop.

Heavy Rain Can Reveal a Partial Blockage

A drain doesn't need to be completely blocked to cause problems.

A pipe may continue carrying enough wastewater during normal day-to-day use even when its capacity has gradually been reduced by a build-up of debris.

Heavy rainfall changes the situation.

As more water enters the system, the restricted pipe may no longer be able to carry it away quickly enough.

Water can then begin to:

Pool around outside drains
Rise inside inspection chambers
Drain away unusually slowly
Back up through gullies
Overflow onto surrounding areas

The rain hasn't necessarily caused the blockage.

Instead, it may have exposed a problem that was already developing.

Leaves, Mud and Debris Can Make the Problem Worse

Autumn creates another challenge for outside drainage.

Falling leaves, twigs, soil and other garden debris can collect around gullies and drain covers.

During heavy rainfall, this material can be washed towards the drainage system.

A layer of leaves covering an outside gully can restrict water before it even enters the drain, while smaller debris may be carried further into the pipework.

Keeping outside drains and gullies clear is therefore particularly important as we move through autumn.

Our guide to how to prevent blocked drains includes further practical steps you can take to reduce the risk of a blockage developing.

What Happens After a Dry Summer?

Heavy rainfall can be particularly revealing when it follows an extended period of hot, dry weather.

During drought conditions, some soils can shrink and move. Older clay drainage pipes may be more susceptible to cracking, displaced joints or other movement as the surrounding ground changes.

We explored this in more detail in our guide to how summer drought can affect older drainage systems.

When significant rainfall eventually returns, the increased flow through the drainage system may expose weaknesses that weren't previously noticeable.

This can make it appear as though the heavy rain has suddenly damaged the drain when, in reality, the underlying problem may have been developing for some time.

Can Heavy Rain Cause Drains to Back Up?

Yes, although the reason isn't always within the private drainage system serving your property.

During intense rainfall, the wider sewer network may also experience unusually high volumes of water.

If the network cannot carry that water away quickly enough, water levels can rise temporarily.

That's why it's useful to consider what's happening around you.

If only one drain at your property is affected, a local blockage or restriction may be more likely.

If several drains are affected or neighbouring properties are experiencing similar problems at the same time, the issue could be further along the drainage network.

Responsibility for drainage problems depends on where the issue is located. Our guide explaining who is responsible for blocked drains covers the difference between private drains and shared or public sewers in more detail.

Warning Signs to Look Out for During Heavy Rain

Seeing water around a drain during an exceptionally heavy downpour isn't necessarily cause for alarm.

What's more important is how the drainage system behaves during and after the rainfall.

Look out for:

Water that remains around a drain long after the rain stops
Outside drains repeatedly overflowing
Water rising unusually high inside inspection chambers
Gurgling from toilets, sinks or other drains
Several fixtures draining slowly at the same time
Unpleasant drainage smells
The same problem returning every time it rains
Wastewater backing up towards the property

Repeated symptoms are particularly worth investigating.

What Should You Do If an Outside Drain Is Overflowing?

If you notice an outside drain overflowing during heavy rainfall, avoid immediately removing inspection covers or attempting to reach into the drainage system.

Instead, start with the visible area around the drain.

If leaves or other surface debris are covering the gully, and it is safe to do so, clearing them away may allow water to enter the drain normally again.

You can then observe what happens as the rainfall eases.

If the water quickly disappears and the problem doesn't return, the drain may simply have been temporarily overwhelmed.

If the water remains or the drain repeatedly overflows, there's a greater chance that something is restricting the system.

Professional blocked drain clearance may then be required to restore the flow.

When High-Pressure Water Jetting Can Help

Where grease, silt, scale or other deposits have accumulated inside a drain, simply removing an immediate obstruction may not always be enough.

High-pressure water jetting uses specialist equipment to clean deposits from inside the pipe and restore its capacity.

This can be particularly useful where a drain has gradually become restricted and only starts showing obvious symptoms when rainfall increases the amount of water passing through it.

What If the Problem Keeps Coming Back?

A drain that repeatedly struggles every time it rains deserves further investigation.

There may be a persistent obstruction, but recurring problems can also indicate damage within the pipe.

This is where a CCTV drainage survey can be useful.

A specialist camera allows us to inspect the inside of the drainage system and look for problems such as:

Cracked pipes
Displaced joints
Root intrusion
Heavy deposits
Partial collapses
Other structural defects

Our guide to what a CCTV drain survey is and when you need one explains how the investigation works and what it can reveal.

Heavy Rain and Drainage Problems Across Norfolk, Suffolk & Cambridgeshire

Heavy rainfall can expose drainage problems in properties of all ages, from older homes with established drainage systems to newer properties where an obstruction has begun restricting the flow.

1st Response Drainage provides professional drainage services throughout Norfolk, Suffolk and Cambridgeshire.

We help homeowners and businesses across the region, including Bury St Edmunds, Diss, Dereham and Stowmarket.

Whether you're dealing with an overflowing outside drain, recurring blockages or another drainage problem following heavy rainfall, our engineers can help identify the cause and recommend the most appropriate solution.

You can view all of the towns and areas we cover on our locations page.

Our Expert Advice

One of the most useful things you can do when a drain struggles during heavy rain is pay attention to what happens once the rainfall stops.

A drain that was temporarily dealing with an unusually high volume of water may return to normal relatively quickly.

A drain affected by an obstruction or underlying defect is more likely to remain slow, continue holding water or display the same symptoms repeatedly.

It's also worth remembering that the weather doesn't always create the drainage problem.

Quite often, it simply makes an existing problem easier to see.

If your drains repeatedly back up whenever it rains heavily, investigating the cause rather than waiting for the next downpour can help prevent a more disruptive problem later.

How 1st Response Drainage Can Help

If heavy rainfall has exposed a problem with your drainage system, 1st Response Drainage can help identify the cause and recommend the appropriate solution.

Depending on the problem, our services include:

The aim isn't simply to get the water moving again. Where problems keep returning, it's important to understand why the drainage system is struggling.

Related Guides

If you're experiencing drainage problems during wet weather, you may also find these guides useful:

FAQs

Why does my outside drain overflow when it rains?

An outside drain may overflow because heavy rainfall is temporarily introducing more water than the system can carry away. However, recurring overflowing can also indicate a partial blockage or another restriction within the drainage system.

Does an overflowing drain always mean it's blocked?

No. During exceptionally heavy rainfall, a drainage system may temporarily struggle with the volume of water entering it. If the water doesn't clear after the rain stops or the problem happens regularly, it's worth investigating for a blockage or underlying defect.

Can leaves cause an outside drain to overflow?

Yes. Leaves and other garden debris can cover gullies and prevent surface water from entering the drainage system efficiently. Smaller debris can also enter the drain and contribute to an obstruction.

Why do my drains only smell when it rains?

Changes in water levels and airflow within the drainage system can sometimes make existing drainage odours more noticeable during wet weather. Persistent smells, particularly alongside slow drainage or overflowing, can indicate a problem that needs investigating.

Can heavy rain damage underground drains?

Heavy rainfall doesn't necessarily damage a healthy drainage system. However, increased water flow can expose existing weaknesses such as cracked pipes, displaced joints or partial collapses.

Should I call a drainage company if my drain only overflows during heavy rain?

If it happens once during exceptionally severe rainfall and the water quickly clears afterwards, professional intervention may not be necessary.

If it happens repeatedly, remains after the rain stops or is accompanied by other drainage symptoms, having the system investigated is sensible.

Are Your Drains Struggling During Heavy Rain?

If an outside drain keeps overflowing, water is backing up or your drainage system repeatedly struggles whenever it rains, there may be more happening underground than you can see from the surface.

1st Response Drainage provides professional drain clearance, CCTV inspections and drainage repairs throughout Norfolk, Suffolk and Cambridgeshire.

Explore our blocked drain service, find your nearest service area on our locations page, or contact us to discuss the problem with our team.

How Heavy Rain Can Affect Your Drains: What Homeowners Should Look Out For