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Planting a sloping garden to reduce flooding?
NorthernJoe
Posts: 660
We have a decent sized, steep garden. Half is fairly mature copper beech, Leyland, Holly, yew and Hazel. The other is nearer the house and more formal garden with trees, shrubs, plants and borders. We took out a few trees and shrubs that weren't doing so well. We have a bit of a gap there to fill but there's other places too.
With the recent, heavy rainfall we experienced water coming up through the floor of the garage. The garage is underneath the house at the front with the house above the garage opening out back onto a patio. The patio has a drain into the drain the gutters run into. The border above is a series of retaining walls at various heights. The soil is above limestone rock that's not too far below the surface in places. We believe the amount of rain that fell over a long period of time meant drains couldn't cope and water went under the house and up through the garage.
I wonder whether there's something to do in the garden to slow the water down. I was thinking if trenches in borders to act as drains sending the surface water to the side of the garden away from the house. Also, planting to slow surface water or ground water.
I'm really not sure what is possible but I hope someone on here knows a bit more. I'm certain a builder based solution is needed but I'm thinking of helping things with gardening solution too. TBH this is probably a very infrequent occurrence, it was seriously wet for weeks then a period of continuous and heavy rain caused theissues. No damage so we probably won't go with an expensive builder option. If a gardening solution helps I think we'll do that.
Any recommendations?
With the recent, heavy rainfall we experienced water coming up through the floor of the garage. The garage is underneath the house at the front with the house above the garage opening out back onto a patio. The patio has a drain into the drain the gutters run into. The border above is a series of retaining walls at various heights. The soil is above limestone rock that's not too far below the surface in places. We believe the amount of rain that fell over a long period of time meant drains couldn't cope and water went under the house and up through the garage.
I wonder whether there's something to do in the garden to slow the water down. I was thinking if trenches in borders to act as drains sending the surface water to the side of the garden away from the house. Also, planting to slow surface water or ground water.
I'm really not sure what is possible but I hope someone on here knows a bit more. I'm certain a builder based solution is needed but I'm thinking of helping things with gardening solution too. TBH this is probably a very infrequent occurrence, it was seriously wet for weeks then a period of continuous and heavy rain caused theissues. No damage so we probably won't go with an expensive builder option. If a gardening solution helps I think we'll do that.
Any recommendations?
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We also have a garage underneath the house. The driveway from the road slopes down into the garage, so we have to have a sump (with a sump pump), to pump away any rainwater. Some people have something called a soak-away, to prevent flooding. A sump pump will cost more, as you need to get them serviced every year or so.
Berms are a good strategy but they need quite a lot of space to be big enough to have an impact. Cheaper than attenuation crates though and easier to do yourself, if you have room.
Land drains running across the terraces connecting into a 'cross' drain to take the flow past the house is possible but will chuck a lot of silty water onto whoever/whatever is downslope of you, which may not be sensible.
“It's still magic even if you know how it's done.”
The garden is effectively a series of borders raised by differing heights. Patio has a 50cm plus retaining wall before a narrow border and lawn then a foot high border the a 50cm plus high border then flat until the halfway fence. Other side it's just a slope with various trees, some big, and woodland ground cover plants starting with snowdrops and beginnings of hellebores in early winter through wild garlic and a few others. I think a vinca variety comes up. Throughout there's dotted around some ferns from the bracken like to the long, flat leaved variety that's slightly glossy. Shrubs, smaller trees and perennials in lower garden. Highlight of the garden is possibly a centrally located copper beech in the upper, "wild" garden.
I was thinking ditches in the midst of the borders to hokd back the groundwater. The that got me into French drains directing to the side, under the greenhouse and down a border at the side of the house. That has established Heather bushes that could be soaking up a bit too. The ditch idea is possibly berms by another name.
The issue is the flood only happens when there's a real rain event consisting of a period of consistent drizzle then a few very heavy rain spells. We had two such events last autumn and tbh with the weather as it had been since it hasn't fully dried out since. Climate change no doubt and it isn't going to get better any time soon. So we need to futureproof a bit by developing a way of coping with the rain and groundwater such that the garage stays dry. That might need tanking out to be sure but I'd still like to use nature and landscaping to help.
There's a section of the garden we've taken out an overgrown shrub and conifer that was mostly brown because a few shrubs and conifers had grown into each other. After cutting back we found a load of paths into the border including evidence that there was once a path down to the narrow lawn or even patio at that side of the garden, above the garage. It's partly bare soil in a kind of rockery or borders in steps going up to the top level of the lower half of the garden (top of the lower garden).