After a heavy downpour, the first sign of trouble is often a gully brimming at the back door and water pooling where it never usually sits. Heavy rain seldom causes a blocked drain by itself. What it does is overwhelm a drain that was already half-full of silt, leaves or roots, because that drain has no spare capacity when the volume suddenly spikes, so it backs up and overflows.
Here is why it happens across Glasgow and North Lanarkshire, who is responsible for what, and what to do when a drain floods in a storm.
Why do drains overflow after heavy rain?
Drains overflow in heavy rain when a surge in surface water meets a pipe or gully that is already restricted. Drains are sized for normal flow, not a cloudburst, so any narrowing a drain was coping with in dry weather becomes the point where the water stops.
The restriction is usually silt, leaves, grease or root ingress that has been building for months. In dry spells the drain still runs, so nobody notices. Add a downpour and the same drain cannot move the water fast enough, which is why a blockage that keeps coming back often shows itself first in a storm. Waterlogged ground adds to it, pressing on ageing pipes and drawing tree roots toward the moisture inside them.
What is a gully, and why does it flood in a storm?
A gully is the grated drain at ground level that takes water from your yard, driveway or the road, with a trap underneath that catches silt and leaves before they reach the pipe. It floods when that trap fills up and water can no longer drain away fast enough, so it backs up over the grate.
Clearing the leaves off the grate often makes no difference, because the trap below is packed with silt and debris. A gully that overflows every time it rains is usually telling you the trap or the pipe beyond it needs cleaning out.
Yard gullies versus road gullies
Not every gully is your responsibility. A gully inside your boundary, in a yard, garden or driveway, is yours to keep clear. The gully set into the kerb along the public road is the council’s, and it drains the carriageway rather than your property. That difference decides who you call, and the responsibility section below goes through it in full.
Why do Glasgow’s older drains struggle when it rains hard?
Much of older Glasgow drains through Victorian combined sewers, which carry foul waste and rainwater in the same pipe. In a storm that pipe is already doing two jobs, so there is little room left when surface water surges, and it can surcharge and back up.
A combined sewer copes fine in normal weather. Push a month’s rain through it in an afternoon and the extra volume has nowhere to go, so older tenement districts in the West End, Southside and East End flood sooner than the newer estates on the edge of the city.
Glasgow has spent years trying to take surface water back out of the combined network to ease exactly this, work led by the Metropolitan Glasgow Strategic Drainage Partnership after severe flooding in the East End in 2002.
Combined sewers versus separate systems
Newer estates are built on a separate system, with one pipe for foul waste and another for surface water, so a storm only loads the surface-water side and the foul drains keep working. Scottish Water no longer normally accepts new surface water into the combined sewers for this reason. If your home is in the Victorian core, that older combined arrangement is part of why heavy rain hits your drains harder.
How do autumn leaves, silt and storm debris block drains?
Rain also carries material into drains as it fills them. Wind and rain strip leaves into gully grates, wash grit and silt off roads and gardens, and drive all of it into traps and inspection chambers where it settles and builds.
Autumn is the worst of it, when a single storm can pack a gully with wet leaves in minutes. Silt washed off the ground settles in the bottom of chambers and pipes and slowly raises the level until the flow chokes.
Any grease already lining a pipe grabs the incoming debris and speeds the blockage up. None of it clears itself once the rain stops, so the gully that overflowed in the last storm will do it again in the next.
Is it my drain or the public sewer? Who is responsible in Scotland
As a general rule in Scotland, the pipes and gullies inside your property boundary are yours, the public sewer beyond the boundary is Scottish Water’s, and the gully in the road is the council’s. The flooding responsibilities set out by SEPA follow the same split. Where the water is surfacing, and whether it affects one property or the whole street, usually tells you which one you are dealing with.
Your private drains and yard gullies
A homeowner or landlord is responsible for the drains and gullies within the property boundary, up to the point where they connect to the public sewer. If the overflow is confined to your own yard gully or your own drain, it is yours to sort. In a tenement, that private section is often shared with the other flats, which changes who pays.
Scottish Water’s public sewers
Once a drain connects to the main sewer, normally at the edge of the property, it becomes Scottish Water’s responsibility. They maintain the public sewers and deal with flooding from an overflowing or blocked public sewer, and they clear a public-sewer blockage at no cost to you. If several homes on the street flood at once, a public sewer is the likely cause, and you can report it to Scottish Water.
Road and street gullies
The gullies along the public road are maintained by the local roads authority, which is Glasgow City Council or North Lanarkshire Council depending on where you are. A flooded road gully, or water pooling across the carriageway, goes to the council rather than a drainage firm or the water company.
Working out who owns a shared or boundary drain is less clear cut, and our guide to who is responsible for a blocked drain in a Glasgow tenement goes through it properly.
What should you do when a drain overflows in a storm?
If a drain overflows in a storm, keep clear of the water and work out whether it is just your property or the whole street before you call anyone. Storm water from a combined system can carry sewage, so it is not something to paddle through or bail out by hand.
If the problem is your own drain or a shared tenement drain, that is when to get it cleared. We cover Glasgow and North Lanarkshire within standard working hours, with on-call cover for genuine out-of-hours emergencies such as an overflow that will not drain or sewage backing up indoors.
An engineer can jet a blocked gully or drain clear and put a camera down afterwards if it keeps happening, so you are not back in the same spot at the next downpour. For drain unblocking across Glasgow, call 0141 673 3535.
Frequently asked questions
Why do my drains overflow every time it rains heavily?
Because the drain is already restricted by silt, leaves or roots and has no spare capacity for the extra water. The rain tends to reveal a blockage that was building quietly in drier weather rather than cause it outright. Clearing the underlying build-up is what stops it recurring.
What is a gully and why does it flood in a storm?
A gully is the grated drain at ground level with a trap beneath it that catches silt and leaves. It floods when that trap fills and water cannot drain away quickly enough, so it backs up over the grate. A gully that overflows in every storm needs the trap and pipe cleaning out.
Is a blocked drain after heavy rain my responsibility or Scottish Water’s?
If the drain is within your boundary, it is yours. Once it connects to the public sewer beyond the boundary, it is Scottish Water’s. A rough guide is whether one property is affected or the whole street, since a public sewer problem tends to flood several homes at once.
Who do I call about a flooded road gully in Glasgow, the council or the water company?
The council. Road and street gullies are maintained by the local roads authority, Glasgow City Council or North Lanarkshire Council, not by Scottish Water or a private drainage firm. Report water pooling on the carriageway or a blocked kerbside gully to them.
Why do older Glasgow properties flood more in heavy rain?
Because much of older Glasgow runs on Victorian combined sewers that carry foul waste and rainwater in one pipe. In a storm the pipe is already loaded, so it surcharges sooner than the separate systems used in newer estates, where surface water has its own pipe.
Is the water from an overflowing drain in a storm dangerous?
It can be. Water from a combined system may contain sewage, so keep out of it, keep children and pets away, and do not try to clear it by hand. Once the drain is cleared and the water has gone, disinfect any surfaces it reached.
Why does my drain gurgle or smell after heavy rain?
Gurgling, slow drainage or a drain smell after rain usually means the drain is partly blocked and struggling with the extra water. Our guide to what gurgling drains and bad smells mean runs through the signs. It is also worth checking local flood alerts through Floodline before a big storm.
Do you cover North Lanarkshire as well as Glasgow for storm drainage problems?
Yes. We cover Glasgow city-wide and North Lanarkshire, including Coatbridge and Airdrie, within standard hours and with on-call cover for genuine out-of-hours emergencies. Call 0141 673 3535 and we will tell you what to expect.
