Rain is part of life in Merthyr Tydfil. The town sits at the head of the Taff valley under the Brecon Beacons, and weather coming in from the west often drops its heaviest rain on the high ground around it. Gardens on the valley sides take water from everything uphill of them, while gardens on flatter ground can sit on heavy soil that holds rain like a sponge.
This guide is a practical look at drainage for Merthyr Tydfil homes. It sets out the signs worth noticing, the main drainage options in plain terms, which ones suit the different kinds of plot around the town, and the points where it pays to get advice. Our home guide on how to stop a garden waterlogging explains the methods in more general detail.
Signs your garden is not draining
Some drainage problems are obvious, such as a lawn that becomes a pond after every downpour. Others creep up slowly. These are the signs we look for on a visit:
- Moss taking over the lawn, even where it gets some sun.
- Puddles that are still there a day after the rain stops.
- Green staining or a tide mark along the bottom of walls.
- Water seeping out through the face of a retaining wall, or the wall starting to lean.
- Paving that has sunk, rocked or grown a permanent film of algae.
- Plants with yellowing leaves or roots that rot over winter.
- Damp patches on the inside of a wall that backs onto the garden.
The last one needs care. Damp inside the house can have several causes, so if you see it, it is worth getting the building itself checked as well as looking at the garden levels outside.
How hillside and estate gardens differ
In Merthyr Tydfil we tend to see two broad kinds of drainage problem. On the older streets built into the valley sides, most of the trouble is water arriving from above: run-off from the hill, the lane behind or the garden next door, flowing down through the plot and gathering at the lowest wall or the back of the house. The ground itself may drain reasonably well, but it is overwhelmed by volume.
On the newer estates and flatter plots, the issue is more often the ground. Topsoil can be thin and the subsoil compacted by building work, so rain has nowhere to soak away. These gardens need the ground itself improving, or water carried off through drains beneath the surface. Knowing which kind of problem you have is the first step to choosing the right fix.
The main options, in plain terms
These are the drainage approaches we use most around Merthyr Tydfil:
- Cut-off or french drains. A trench filled with clean stone, often with a perforated pipe, dug across a slope to catch water before it runs further down the garden.
- Land drains. A network of perforated pipes in gravel beneath a lawn, carrying water away to a suitable outlet.
- Channel drains. Slotted channels set along the edge of a patio, path or driveway, taking surface water to a gully.
- Drainage behind walls. Stone backfill, a pipe and weep holes behind retaining walls, so water does not build up and push the wall over.
- Regrading. Reshaping levels so water falls away from the house and towards a border or drain.
- Soil improvement. Breaking up compaction and adding topsoil, grit and organic matter so the ground absorbs rain better.
- Soakaways. An underground chamber or rubble pit that lets collected water soak into the ground slowly.
Where the water ends up
Collecting water is only half of drainage. It then has to go somewhere safe. A soakaway only works if the surrounding ground can take the water, and in heavy, saturated upland soil it can fill up and stay full. We test how quickly water drains from a hole before relying on one.
Water must not be directed onto a neighbour’s land, and rainwater should not go into a foul sewer. If you plan to link to an existing drain, check what it is and whether you are allowed to connect to it with Merthyr Tydfil County Borough Council or the water company first. We are landscapers, not drainage engineers, so on bigger schemes we will say when outside advice is needed.
Plants and surfaces that help
Not every wet patch needs a pipe. A low corner that is always damp can become a rain garden, planted with species that enjoy wet roots and slow down run-off. Raised beds lift vegetables and flowers above soggy ground. Gravel paths, bark and permeable block paving let rain soak through rather than running off. A water butt on each downpipe takes some pressure off the garden in a storm and gives you water in a dry spell.
For ideas on combining these into a layout, see designing a garden for Merthyr Tydfil’s wet climate.
Drainage before lawns, patios and walls
Drainage is best sorted before anything else is built, because putting it in afterwards means lifting what was just laid. New turf on waterlogged ground turns to moss. Patios on wet ground sink and crack. Retaining walls without drainage behind them bulge and eventually fail.
So when we plan new turf, a patio or a retaining wall in Merthyr Tydfil, drainage is part of the same job. Our local guides to laying turf in Merthyr Tydfil and terracing a steep Merthyr Tydfil garden show how it fits in.
Getting advice on a wet garden
If your garden is wet and you are not sure why, the best first step is for someone to look at it, ideally soon after rain. Tony and the team will walk the garden, check the levels and soil, and talk through the options in plain terms. Drainage is part of our landscaping and garden design service, and there is more about our work in the area on the Merthyr Tydfil landscaping page.
Get in touch for free advice and a free quote. A few photos of the wet areas, taken during or after rain, help a lot.
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Questions People Ask
Why does my garden flood when the rest of the street seems fine?
It is often down to levels. If your garden is lower than those around it, or sits below a slope, it may be taking water from several neighbours. Compacted soil and blocked old drains can also be to blame.
Is a french drain the answer for a sloping Merthyr Tydfil garden?
Often, yes. A cut-off drain across the top or middle of a slope catches run-off before it reaches the lower garden. It still needs a safe outlet at the end, which we plan at the same time.
Will a soakaway work in Merthyr Tydfil?
In some gardens. In heavy clay or ground that is saturated through the winter, a soakaway can fill up and stop working. We test the ground before suggesting one.
Can drainage be added without ruining my lawn?
Some disturbance is unavoidable, but trenches can be neatly backfilled and returfed, and the lawn usually recovers well. Often the drainage is done as part of relaying a lawn anyway.
What affects the cost of drainage work?
The size of the area, the type of drain, depth, the slope, access for digging, where the water can go and whether turf or paving need relaying afterwards. We explain it all in a free quote.