No, your garden cannot be the first line of defence against flooding

Flooding means means we need continental green corridors

I sometimes wonder if I may be over critical and I do start this article with a roasting of the ‘Flood resilient garden’. But then again, I follow criticisms with positive stuff about what we can do, as I do again here.

"Flood Re has been working with designers Dr Ed Barsley and Naomi Slade to bring the Flood Resilient Garden to life at Chelsea Flower Show 2024." On their webpage there is a pretty image of a garden with a plant list and there are accompanying videos. “The Flood Re Flood Resilient Garden is designed to be both a relatable enjoyable and beautiful space, and to help reduce flood risk”.

I’m not sure what ‘relatable’ means in this context but anyway ….

Don't misunderstand me, changing the way that people run their gardens is a good thing if the gardens are just rolled-mowed lawn or paved over etc. Correctly dealing with flooding is also essential, more on this later. The garden promoted by Flood Re and the text which goes with it is frankly somewhat misleading.

Let us take this part of their text as an example "The swale forms a stream, channelling rainwater into a feature pond where it can gradually soak away".

One : a swale is specifically a ditch that follows a contour line and whose function is to slow water flow in order that it may infiltrate downwards into the soil. A swale does not direct water towards a pond, if it does it's not a swale it's a ditch, I can understand that the writers probably thought that asking people to dig a ditch across their garden sounds less eco-sexy than building a swale.

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Two : : flood water isn’t clean, especially where flooding occurs in areas that have been built on. Sewage systems overflow, quantities of pollutants and debris are carried by the water and I wonder who would want all this ending up in a garden pond.

Three : the most important thing. The idea that flood water could flow along the ‘swale’ and be absorbed by a pond is simply absurd. The pond will overflow and the water will continue it’s journey, probably into the house. Well designed swales and ponds/lakes/etc have overflow points, the overflow water continues in a guided way to other structures and/or more level ground where the flow can spread, the overflow points are reinforced to ensure that they don’t erode. They protect the swale berm from being washed away and prevent uncontrolled overflow from the pond.

These type of lite-green and misjudged approaches really don’t help and are frankly pretty annoying. One wonders if the 2 designers have actually experienced a flood. If they haven’t then they should because, as with a wildfire, the reality is shocking and they both ruin property and people’s lives, not to mention the impact on wildlife.

OK, enough criticism and on to what we should be doing.

For a start stop building in areas that are prone to flooding! This would seem self-evident but what is obvious is too often secondary to profit making.

Flooding cannot be addressed by piecemeal approaches, it requires holistic, integrated landscape management. This point brings me back to my last article about continental green corridors and of course Permaculture.

Changing climate means we need continental green corridors

A point I didn’t make in the above article is how these green zones, integrated with blue zone areas are an answer to flood mitigation. They involve local landscape management that is integrated with the initiatives of other local areas in order that the whole landscape becomes part of the flood mitigation. If we think in terms of bio-regions then we are off to a good start as one basis for defining a bio-region is hydrology.

A further point is that landscapes are dynamic, they change. Up until 1995 the river here flowed along a course which is 50 metres away from where it now runs. This has brought it much nearer the house, fortunately the buildings are still several metres higher than the river.

Holistic landscape management takes this into consideration and well designed flood mitigation systems are also dynamic, they have to be as the climate is changing. Since the 1980’s we have been predicting more frequent and more powerful extreme events and this is what we are experiencing. 500 year floods (0.2% chance of occurring or being exceeded in any given year) are becoming 100 (1% probability) year floods and the latter are becoming 10 year floods (10% probability).

Floods can’t be avoided, we cannot control when and where storms may occur nor their severity. What we can do is respect the Permaculture principle of ‘work with natural systems and flows, not against them’. Decades of canalising rivers, destroying flood plains and creating thousands of hectares of non-porous artificial surfaces has to stop.

We also have to move away from crisis management to crisis prevention, it’s all very well to rush the Fire Brigade and the Army in to deal with flooding but it would have been better to mitigate the conditions that cause catastrophic floods. Again this needs at the very least a bioregional approach to landscape management and, even better, continent wide integrated approaches.

I have often worked on projects where the local people have told me that they have a water problem, they have rainy periods followed by dry seasons and droughts. They don’t actually have a water problem, they have a water management problem. Even in countries such as the UK periods of high rainfall are followed by hosepipe bans. This, in a relatively water rich country is simply absurd. There is a lack of reservoirs that could accommodate excessive run-off and turn the problem into a solution.

Sticking with the UK there is a strange situation where water companies who run sewage works regularly release untreated sewage into water bodies. They say that they have to do this during periods of high rainfall as their sewage storage capacity is overwhelmed. Sewage treatment must also be considered when we are addressing holistic landscape management. If we increase the number of water storage systems then it’s best that the water flowing into them is as clean as possible. Correctly managed, sewage treatment removes the sludge and the outflow is clean water.

All that said sewage water also contains a cocktail of residues from medications and things like per- and polyfluoroalkyl substances (PFAS). This brings us again to the essential point, that we must think holistically, which is the major strong point of Permaculture design. Removing traces of pharmaceuticals from sewage water is very difficult and simply addresses a symptom and not the cause. Reducing the need for pharmaceuticals means that we have to look at why people need them and change things so that they don’t. The response by the chemical industry to the so-called ‘forever molecules’ such as PFAS problem has been to change from long chain PFAS molecules to short chain ones. Studies have shown that these are as bad for human and biosphere health, the real answer is to stop using persistent, health destroying molecules in our consumer products or anywhere else.

As I discussed in the green corridor article, farmland must be included in any bioregional or continental approach to landscape management and flood mitigation. Farming practices have to change, a few years ago I watched a field being deep ploughed, then the rain came and the water sheet flowed off the ploughed land. It, and the eroded soil flowed into a downslope neighbouring restaurant ill-equipped to deal with such a sudden and copious sharing. Ploughing removes the vegetation that can calm sheet water flow, it also compacts the soil meaning higher levels of run-off. Correctly designed sophisticated farms have hedgerows, they have trees (agroforestry) and the soil is never left without a cover of vegetation. Ploughing is replaced by seed drilling into crop residues, or seed drilling into rolled and crimped cover crops, both help with reducing water run-off and controlling it’s speed. The use of water polluting agricultural synthetic chemicals, from nitrogen through to pesticides, must be replaced by nature based solutions.

This is vision I wrote about in the last article:- continent spanning green corridors that are a mix of completely wild areas, semi-managed wild areas, urban green space and agroforestry based farms all connected together to create contiguous green zones across the continent. As I hope I have shown in this article, these green corridors and blue ones must also be designed to mitigate flood risk. This will involve us all working together, farmers, gardeners, home owners, everyone. As I have also tried to point out, complicated problems need complex, integrated solutions. Flood mitigation means changing where and how we build, how we treat sewage, how we farm. Correct water management also means creating systems that improve people’s health and changing our industries so they no longer contaminate our water with forever molecules.

Flood Re's have organised a scheme that allows people to claim up to £10,000 for flood resilience measures. This is on top of the cost of work to repair damage and replace property damaged by a flood. This sounds like a good thing and next time we get flooded maybe we’ll get together with the neighbours and each of us claim the £10,000 and put all the money into a community fund. Then, ideally with the help of an experienced Permaculture designer, use the fund to design and install flood mitigation systems that are integrated into a bioregion sized system.