Flood prevention - slow water

Here in the UK, its Flood Prevention Week, and just to ram home the message, we've had a pretty wet week. Here are my 5 tips to creating a flood resilient garden which will help our communities too!

We’re only halfway through Flood Prevention Week and already my garden has received 40mm of water, on top of what was a really wet September. One year ago, much of the country was being battered by Storm Babel which, according to the Met Office, saw the third wettest three-day period for England and Wales since 1891. Thousands of homes were flooded.

Records continue to be broken and we can expect this to continue as warmer air holds more moisture, which means more rain. But on a positive note, there is so much that gardeners can do to make their gardens more flood resilient, and, in doing so, we can make our communities more resilient too. So we all need to do something, however small!!!

Slow it, spread it and sink it

This phrase has been around a while and was first coined by Brook Dolman, a Californian water conservationist. The idea behind this important phrase is to slow the rate at which rain disappears down the drain, to spread the water out and get it in the ground. Brook is one amazing guy and I urge you to listen to this interview with him on the Climate Water Project Substack, which I highly recommend.

There is lots of information on the podcast but there is one phrase from Brook that I want to quote, which I feel sets the scene for this post - I think it’s brilliant, and I hope you do to.

“I coined that phrase. My riff on it is “Slow it, spread it, sink it, store it, share it”. Its sort of of like Carlo Petrini’s slow food movement. I thought about this idea that I call the slow water movement. Because we’ve been having this fast water movement. We’ve been living in the drain age, where the dominant land use paradigm of North America for hundred of years since settler colonies is - kill the beaver, genocide the native people, drain the wetlands, ditch the land, and dehydrate it for settlement patterns. We have a drain age paradigm, where we have been draining, paving, piping, polluting, plundering, and making it go away as fast as possible and as dirty as possible. We want to slow it, spread it, sink it, store it, and share it, and keep it around as clean and as long as possible…. “

Tip 1 Observe

My first tip doesn’t require you to do anything but look and learn. When it’s tipping down, go outside and walk around your garden. Where is water collecting? Where is it draining away? Are there any gutters overflowing etc? Through simple observation you can learn how water moves through your garden and that will help you plan for the future. For example, I know there is an area in my perennial veg garden that is prone to flooding, but by going out in a heavy rain storm, I noticed that most of the water was coming off the drive. So I should be able to intercept that water and stop the water collecting. You have to be out there to see the flow of water flow, once it stops raining, the flow disappears, and leaves you none the wiser.

While it was raining I could see the water seeping along the path from the drive

Just a few minutes later, it stopped raining and the flow of water disappeared

Tip 2 Slow water butts

We tend to think about water butts (rain barrels) as things you use to save water, but they have a vital role to play in slowing the flow. Research by Southern Water on the Isle of Wight found 40% of the water in their sewers came from rainwater running off roofs, causing the sewer to become overwhelmed during heavy rain, so they have designed a slow flow water butt. The overflow is positioned so the water butt only fills to about 2/3 capacity. When the rain is heavy, it quickly fills to the top and then takes about 4 hours to slowly drain away. This simple idea gives the drainage system a breather and in the trial area there were no sewage discharges despite heavy storms. You don’t have to use one of these slow flow butts. When you know a heavy storm is coming, go out and let the water drain out of your water butts, so when the storm arrives you have plenty of water capacity. Just imagine how a community of gardeners emptying their water butts ahead of a storm could reduce the flood of water down their drains. Community action folks!!

Tip 3 Keep it permeable

We have lots of hard surfaces in our gardens - drives, paths, patios etc. Do we need them all? Remember impermeable surfaces = more flooding as the water can’t drain away. But there are some new landscaping products that will allow you to have a new permeable patio etc. The term to look for is resin-bound. We have relaid the cobbles outside of our backdoor and instead of using traditional mortar, we chose a resin bound mortar. The tiny pores in the mortar allow water to percolate through into the ground.

Our new cobbles - resin bound mortar means water drains straight through

The front garden is permeable. We have resin-bound gravel on the steps and in front of the house and recycled bricks bedded on sand, while the rest is recycled crushed aggregate

Tip 4 Plant more trees and shrubs

I spend a lot of time telling people to plant trees to cast shade and reduce temperatures in the garden on a hot summer day, but they have just as important a role to play when its wet. They slow the flow of water by intercepting rain. Some of the rain remains on the leaves where it may be transpired, and the rest hits the ground with less speed. This means less run off and soil erosion etc.

Their deep roots are important too. They help the water to percolate deep into the ground so more water is stored in the soil. Research has found that water infiltration rates can be 60 times higher within tree shelter belts than on the adjoining farmland.

Its not just trees and shrubs that are important. Choosing plants that have deep roots will improve your water resilience too.

Tip 5 Manage your soils

Soil has a huge capacity to hold water, so you need to look after it. One approach is not to dig. The turning of soil destroys its structure, damages plant roots, breaks up fungal hyphae and destroys earthworm burrows (as well as allowing sequestered carbon to oxidise). This can leave your soil more vulnerable to waterlogging and flooding.

I observed the benefit of no dig first-hand on our farm. We have a small allotment plot that was established 14 years ago. At the time, half of the allotmenteers were no dig. They experienced surface water flooding after storms but interestingly, the water soon drained away from their beds, unlike the puddling on the dug beds. There were quite a few no dig converts after that! The key to no dig is adding a thin layer of compost to the top of the soil each year, which improves soil structure, and water holding etc.

Mulching is important too as it creates a friable surface over your soil that will improve the infiltration of water as well as boosting the water holding capacity.

If your site is prone to flooding, then creating raised beds will help to keep the roots of your plants above the level of the water. On some sites, I have seen allotmenteers create trenches alongside their beds to carry the excess water away - a variant of a swale.

These are just a few ideas to boost water resilience in your garden - there are many more which I will cover over the coming months. I have written about flooding over the last year and you can find those posts on the website. They include My garden’s been flooded, what can I do, and Waterlogging and worms

Happy Gardening

Sally

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Talks

I am talking at a number of venues in the coming weeks. Most of these clubs allow non members to attend for a fee.

19 November Mayfield Horticultural Society by zoom

21 November University of Bristol Botanic Gardens

23 November I am talking at the inaugural LandAlive conference at the Bath and West showground on Sat 23 November. The topic is on creating a climate resilient allotment.

4 December Castle Cary Gardening Club

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