Monday, July 25, 2016

Dealing with Soggy Soil

Sometimes you want water, sometimes it's too much.
Right now it's winter and a lot of people are talking about being waterlogged and muddy and standing puddles and worrying about root rot.
Yet in summer or drought years those same plants in the same soil want all the water they can get.

Nature has cycles. Yearly seasons and in Australia we have the fun of El Nino in unreliable ten or so year cycles being a major driver too, more so than any other continent.

For growing plants water is a good thing. Water infiltrating the soil is a good thing. There is no better place to store water.
Lots of things affect this. The type of soil, sand, clay, rocky etc. Slope and shape of the land. Plants root systems.

Sandy soil doesn't hold much water. It flows through quite quickly.

Compacted clay stops water. Most farm dams are just clay run over by a bulldozer to compact it.
Clay with stuff in it, such as rocks or tree roots will leak.

Organic matter in general acts like a sponge and stores water. Some better than others. Things such old wood, mulch, bio-char etc

Water flows down hill. Pretty obvious there,  but that also matters underneath the surface.
Fast flowing water over the surface can be quite destructive. Removing topsoil or even plants, especially shallow rooted annuals.
Water that doesn't move can become stagnant and lacking in oxygen.

Most plants don't like wet feet, the roots sitting in water, it can rot them. Especially most 'normal' plants we eat and deal with. Look at most nursery tags and they say 'well drained soil'
Not all plants are like this. Go visit a creek or wetlands and there is a profusion of plants.

Plants roots are designed to draw water up. They are surrounded by their own little micro-ecosystem of fungus and bacteria acting in symbiosis. They also modify their surrounding environment to make things work better for them.
They drive their roots down, breaking up clay so water flows down more freely. They bind together sandy soil so it holds water better.
This is part of why perennial plants are good, they keep growing deep, wider and complex root systems that modify the soil.

But plants are slow, generally taking years to make changes. They can't do everything themselves.

If you pick the right spots a lot of water harvesting and flood control can be automatic.
Observe where the weeds look happy and green. Where the soil looks washed away and abraded by floods. Where the soil has deep black organic matter mixed or is cracked and dry or solid clay.

But no matter what you probably want to modify the environment for your growing requirements to some level.

This can be large scale earthworks with bulldozers and diggers.
or small directed trenches with your trusty pick-axe and logs and rocks placed in the right spot.

The theory is the same and frankly the small scale is often more useful and practical.

Here are a few of the earthworks structures and how they help with collecting water in the dry and controlling water overflow in the wet.

Swales are one of the most commonly mentioned in a permaculture context. Contour channel or infiltration ditch.
These are a trench that run the width of a slope so water as it flows downhill, is caught in the swale and then sent under the ground.

Below the swale is often a mound. Plants, perhaps fruit trees, are then on the mound where they are higher but the roots have a chance to reach down into the moist soil.
The bottom of the swale may also have aquatic plants or rocks.
The aquatic plants can drive their roots down and help aerate the water.
The rocks don't stop the water, they help widen the infiltration and lower the watertable and can completely fill the channel so people don't trip or fall in. :)

In drier times the water flowing down hill is caught and sent somewhere useful.
Gardens are then placed downhill and make use of it.

Depending on slope there may be a series of swales and gardens making use of the captured water.

These structures also need to consider wetter times. If the ground is fully saturated with water it will just sit there. The root systems and improved soil structure may let the water infiltrate sufficiently, but it may not. The water may need to be directed away.

Water flows downhill.
That is the most important thing to consider.
You want enough to water the plants.
But if it gets over a certain level you then want it to flow somewhere else where it isn't being destructive.

The end of the swale can have a lip on it, the maximum height you want the water to get to, once passed it flows into another channel.
Unlike the swale which is all at one height and so full with even water that sinks into the soil, the drainage channel makes use of slope and gravity.
One end is deeper and so that is where the water goes.
This can be directed to a storm drain, to another swale or down hill, towards a creek or a dam or a bog or wetlands.
or perhaps a chain of those filling each one to its useful capacity and then overflowing to the next. Slowing and making use of the water.

A good garden scale example is a bog garden.
The overflow from a swale or maybe even just directly down channels is sent to a hole. It is deeper than the root systems of plants you want to avoid being waterlogged.
At its simplest is it just a hole that fills with water and gets it out of the way.
The trouble with just a hole is that the water will probably be stale and start to degrade the soil structure, so it may crack once it dries out.
But a better use is to make use of the various ways to make it infiltrate water into the soil safely. Add rocks to widen the surface. Add aquatic plants to use the water, especially ones that can cope with being dried out and then recover once water returns.
Plus it is a lovely garden feature and can be a home for frogs and turtles and water birds.

What structures do I have at The Wallaby's Rock Garden?
Before planting gardens or making any earthworks I observed for a year. The water flows was a major part of that.
The property is all on a slope. Starting at a ridge, then the main garden area, then another forested slope, then a plain, then the creek.
Very first there is shallow channels that direct water downhill towards gardens. Up top being dry is more concern than floods. These channels end in a T in swales above gardens. So they act to catch and infiltrate water into the gardens soil. The swales go the width of the garden. In case of flood the water merely flows around the gardens, continuing downhill without further direction.

The main gardens are placed downhill of water flow. Some have small swales to slow the flow downhill and send it into the soil before the garden. This helps keep them watered in summer and in winter this helps the gardens from become too boggy as the water is slowed before it gets there.
Most gardens are raised no-dig beds, not actually set into the raw soil, but the plants root systems would have sunk into there, the mix of trees, perennials and annuals at differing depths.
A lot of the water over winter is collected in the transient wetlands which acts as a gigantic swale, capturing that water before it flows underground to the primary beds.
The ground is uneven and has various mounds, mainly of rocks, to keep flood waters in place and channels to direct overflows around the edges of gardens and constructions and send water down hill through the forest.
Other garden areas in the forests have their own swales and raised mounds.
As the water reaches the plains below there are more swales and channels, slowing the water and infiltrating it again. Keeping it higher and in the soil for longer before it all finally flows down to the creek which in the end carries the water away to the river and the ocean.

Most of the channels used are not simple on-contour swales or drainage ditches but channels at appropriate angles, slopes and depths for what I want, but still using the same concepts.

So in short, a garden may be a series of infiltration trenches or swales, storing water for plants below them.
In flood the swales overflow into a drainage channel then sends the water to fill a bog garden, in the case that is overfilled the water is then finally directed to the storm drain.

Earthworks and water flow is a huge topic with many variations.

Especially for large scale acreage, keyline design is a good topic to look into, this deals more with larger flows of water than I'm particularly referring to here and controlling the destructive effects it can have on landscape. 

This has been a pretty soggy winter but really not all that extreme and you Need to plan for extremes. Dry weather where you capture all the water you can for your poor thirsty plants. Floods where the water is directed somewhere non destructive.

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