UPPER COURSE
Slowing the flow of water entering, and passing through, the upper catchment, will put less volume pressure on the rest of the river system, reducing the risk of flood.
This page provides information on the following nature based solutions to help slow the flow of water into the middle and lower courses of a river system. Use these links for the stratergy you would like to investigate.
Forestation
Planting trees can help in flood mitigation by slowing and reducing the flow of water down a hillside. The tree captures water in its canopy as well as in its roots. They also help to reduce erosion of soils that would otherwise clog waterways.
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Trees reduce flood risk from the top to bottom. Lots of raindrops that land on leaves evaporate straight into the air- so less water reaches the ground. And, leaves intercept rainfall, slowing the rate that water flows into rivers and reducing the risk it’ll burst its banks. (theecologist.org/2019/mar/14/planting-trees-tackle-flooding)
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Things to consider -
Who owns the land?
What variety of trees would grow successfully in that location?
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Further Reading -
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Leaky Dams Back to top
Leaky dams are dams built to mimic natural river blockages which slow the flow and temporarily store water. They can be built out of felled trees and do not require complicated engineering. Some studies have shown the use of leaky dams to spread the incoming water from a big rain event, to a week or more, instead of all the water arriving downstream in one day.
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They can be built in steep narrow sections of the river to maximise holding capacity or in wide shallow areas to spread water across upstream flood plains.
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Leaky dams may be built above the channel bed to allow fish passage.
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Things to Consider
To have the greatest effect, a series of leaky dams should be built along a river. The more leaky dams, the greater the effect.
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Further Reading
https://www.sciencedirect.com/science/article/pii/S0022169423013914
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Hillside Swales Back to top
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https://www.youtube.com/watch?v=we_cDXZFisE (Swales on Contour can Drought-proof Gardens, Farms and Pastures with Water Harvested Passively)
https://www.youtube.com/watch?v=9WLe_OJsaMM (Taking a food forest garden to the next level - swales, observation, and maximizing water)
Swales are ditches dug along the contour lines of a hill. They reduce the volume of water entering rivers by capturing it on hillsides, arresting erosion, and facilitating infiltration.
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•Should be dug along the contour of the hill so as to reduce downhill flow.
•Lose soil should form a berm which is planted. This berm facilitates the soaking of water and trees both absorb water and protect against erosion.
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Things to Consider
The steeper the slope and more water expected, the deeper the swale should be.
May not be feasable for a very steep slopes. Slopes up to about 8.5 degrees are best.
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Further Reading
https://www.lfwseq.org.au/swales/ https://www.tenthacrefarm.com/permaculture-swale/ https://permacultureapprentice.com/food-forest-swales-layout/