Food and floods

The greatest challenge of our era

Wherever you look the headlines are about the floods and how they are creating food shortages and escalating prices.

My interest is in how to grow plants for a healthy gut brain which requires very careful management of the moisture level but I accept that this is a minority interest. But everyone has to eat so these floods and the food shortage are everyone’s problem. How to feed 8 billion people the right sort of food in the midst of a climate crisis is among the greatest challenges of our era. I talk about this more in my article on the global food crisis.

What can I do?

So the question is what could I do about it?

I can’t stop the floods, that is for the Climate Change movement – I have solar panels and batteries, and walk and bike rather than use the car wherever I can, but I am just one person, so what can I do to mitigate these floods?

The first thing is to understand why we get these floods – and it is a bit more complicated than too much rain.

Two types of floods – upstream

There are two types of flood which is well illustrated in my home town of Bundaberg based on the Burnett River which starts at Mt Gaeta and flows 435k to the entrance at Burnett Heads.

Floods occur with rainfalls above 100mm over a period of hours or even days. That amounts to 1,000 tonnes of water per hectare and the Burnett basin has an area of 32,220 square kilometres; let’s not get bogged down in calculations but you can see that is a huge volume of water that has to get out to the sea at the narrow Burnett Heads.

Unfortunately the river at Burnett Heads enters the ocean through a narrow channel and it simply cannot handle that volume of water so the flood builds up back from the head, flooding further and further inland.

I know, I have done my stint in my rubber ducky ferrying people from their upper storey windows.

OK, you are looking for a solution so what can I offer? For this type of flood sadly not much. I know that the Incas had floating gardens which are now becoming widely adopted in flood-prone countries like Bangladesh.

Two types of flooding – local inadequate drainage

But there is a much more common type of flood which is even closer to my home, actually right in my backyard. Looking at my backyard it seems almost flat but there is actually a slight slope with water falling on blocks just uphill and flowing through my block. Again no calculation, but at 1,000 tonnes of water per hectare you can see it would soon add up to a lot of water flowing through my block.

Gbiota beds in the drought

It was in 2015 that I set up my flood-and-drain Gbiota beds. At that time we were more worried about drought than floods and we are in that belt of land where the great deserts form. Just start walking west and you would end up in the Simpson Desert.

These beds worked great until about three years ago when La Niña came and we started to have seriously heavy rains. My Gbiota beds became waterlogged for short periods of time.

Not good, as the whole point of a Gbiota bed is to breed beneficial gut biota in the soil and that means the soil must be nicely moist but not too wet – Goldilocks moisture.

Flood proofing experiments

I needed to rework the entire beds to make them more flood-resistant and this was a great opportunity to experiment.

In the first two beds I ran an experiment with one bed having a plastic liner and the second bed just relying on soil compaction. This is described in my article on Wicking Soaker beds so I won’t go into details here.

50 year floods every five weeks

But by the time I had got around to reworking the third bed we had already had three 50-year rains which now seem to occur every five weeks. Great for testing flood-resistant beds, lousy for growing plants.

There is a bit of slope on my block and I had built the levels up so the Ag pipe, which acts as both a filler and drainage pipe, was pretty much at the parent soil level so to be honest I had not given much thought to the water flow from my neighbours’ properties – I am human.

Science and serendipity

Now for those of you who think science is a nicely planned and organised operation – let me disillusion you – serendipity plays an important role.

And serendipity came in the form of 190mm rain in 30 hours.

Water came from all the blocks uphill, straight through my shed onto my beds.

Time for a cup of tea and a bit of a think.

Rethinking beds

It is clear that just trying to design a bed so it does not get flooded and waterlogged is not enough – we have to ensure that the inevitable floodwater is adequately diverted before it reaches the beds.

And it is not sufficient to just think in simple terms of drainage and gradients. I did not talk about the 1,000 tonnes of water per hectare for fun – we must think about water like an express train; water is heavy stuff and has a lot of inertia even if only flowing at a few kilometres per hour. If there is some obstacle it will simply keep on going up and over, what engineers like to talk about as converting kinetic energy into potential energy.

I learned all about this during that thirty hours of rain and had to go out in the pouring rain and dig channels and diversions to stop the water getting onto my beds in the first place. It worked then but now I have to wait for the next fifty-year flood which at the current state will be in about five weeks to see if it has really worked.

If it really does work again in the next flood, as it did in this flood, I then only have to consider getting the water that falls on my beds away.

Farmers of old

When I was a toddler (a very long time ago) I had uncles who worked on farms and they spent a lot of time on what they called hedging and ditching. Doing precisely what I am doing now, trying to protect the fields from water flowing onto them.

Now of course we have ripped up all those hedges and ditches to make monster fields.

Whatever would Dr Who say about the wisdom of that?

Avoiding water logging

It is inevitable that with that amount of rain, beds not designed for water flow will become waterlogged – there is just too much rain. But what we can aim for is to get that water away as quickly as possible.

Plants will survive quite happily for a few days even if their roots are totally immersed but then most plants will just die, unless you are living off watercress or mangroves.

The lower roots will die if they are immersed in water but if the upper roots are not flooded the plant will survive and quickly regrow the lower root system. Our minimum aim should be to ensure the top layer of soil can drain easily, but ideally we should ensure the whole root system drains.

Soil ain’t software

I used to earn my daily bread writing software which is great. If you screw up just hit the delete button and start again.

Growing plants is not that easy. You have to move on from where you are and not some theoretical ideal position.

If I was building new beds from scratch and had a supply of soil I would certainly consider building the entire bed above ground level but in the real world I am halfway through modifying an existing bed – so that is my starting point whether I like it or not.

Making drainage trenches

So I dug up the existing ag pipe which was over 300mm below the current surface and filled the trench up so the base was only 50mm below the parent soil level. I then made a ridge with my classic mixture of grass clippings and organic waste followed by chicken manure and rock dust.

I then dug a trench either side using the soil to cover this ridge and smoothed it all out.

I made sure this trench extended beyond the beds themselves to an area where the parent soil was low enough to provide effective drainage.

Speculative research or just plain daft

The peak of the ridge is some 300mm above the base of the trench which I am sure would provide adequate drainage to get any water that falls on the bed away fast enough.

On the previous two beds (which were above the parent soil) I had partially filled in the trench with whatever organic waste I could lay my hands on but largely grass clippings.

I am not that keen on putting organic waste directly into my beds as labile (young) compost often contains pathogens and growth inhibitors. By partially filling in the trench with this waste I had made a really nice and convenient composting area so when I had to remake the bed (as is essential to keep that highly porous layer above the pipe) all I would have to do is to dig down to the pipe (which I like to remove and clean out) and rake the compost to cover the pipe.

Getting the water away in practise

I had noticed that in beds one and two that even though I had partially filled in the trench with this organic material it was still adequately porous to let the water drain through.

On the basis of ‘try before you die’ I am therefore filling this new trench with fresh organic waste. (It makes a nice mud-free path to walk on to work on the beds).

I will let you know if it drains properly after the next fifty-year flood which I am expecting in about five weeks according to the current weather pattern.

The punch line

We live in the internet age – the virtual world – but treacherous. If the virtual world on the internet is different to the real world then the consensus is that the virtual world is right and the real world is wrong.

I believe in experiments but how do I test if my design will work? I can’t just go online and order a flood – I just have to wait for that fifty-year flood to come – maybe this week, next week, next year or most unlikely in fifty years.

But let us just look at some flow calculations. Consider a 10 metre long 1 metre wide bed. In a 100mm rain storm that gives 1,000 litres. Most of that will flow straight off the bed and into the side trenches. Without getting my slide rule out the trench would easily handle that flow. (PS if there is any reader out there who knows what a slide rule is please email me – there are only a few of us left).

Some water will soak into the bed but the Wicking Soaker bed has a natural drainage, so even if the soil does become temporarily waterlogged it will soon drain away.

If I am right and my bed does not become waterlogged, time for a celebration.

But I have been in the innovation business long enough to know that you may think you know something but you don’t actually know you know something until you have tested it and know for sure.

So the punch line is we can be pretty confident that if you can stop water entering the bed area from outside that the bed area itself is going to be able to cope with the rain that actually falls on the bed.

Although I feel confident that is a valid conclusion, if I have missed something my plan is I can easily fit a drainage pipe to take the water from the Ag pipe straight into the drainage trench. Yet another day digging away in the pouring rain – all so we can eat.

What a hassle food is

Why does not someone invent mobile phones we can eat when we have finished with them so we don’t have to bother with food. Apple pie anyone?