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Designing for periods of excess water  RSS feed

 
Casie Becker
gardener
Posts: 1474
Location: Just northwest of Austin, TX
117
forest garden urban
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We're squarely in the center of our rainy season here, and if you follow weather news you'll be seeing a lot of flood rescues right now. A lot of discussion centers around water management, especially in dry regions. Determining how to survive the summer drought is one of the most challenging parts of gardening in my region. With all the attention paid to conserving water, I think sometimes people forget to plan for excessive rains. How do you keep that 12 inches of rain in one week from causing all your crops to rot in the ground?

I build my garden beds slightly raised or on slopes. When we do get excessive rain I've been working on shaping the land so that water accumulates around the beds in ways that can trickle or wick into the growing area without actually flooding the growing spaces. Swales upslope of the raised beds, or pits of organic material under the beds both seem to work well. I'd still like to find a way to completely eliminate summer watering, but this has so far been a good compromise that keeps me from losing plants to flood while still capturing a lot of the rainfall.
 
Tyler Ludens
pollinator
Posts: 9740
Location: Central Texas USA Latitude 30 Zone 8
180
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Super important topic in our region!

My kitchen garden is a terrace on a sloping shelf of rock. It seems to drain pretty well. During last year's floods it received flooding runoff from upslope, but aside from a couple little squash plants who got washed out, everything else seemed to do ok. I don't seem to be having serious water-logging problems although the soil is still too much clay and not enough organic material and I think this affects some plants which prefer better drainage. I have buried wood to retain moisture through dry periods, and it seems to be helping to even things out. I think having growing beds of different heights helps to give more plants a chance to avoid drowning, while being able to reach down to water stored in the buried wood.

This year our major focus has been on water management, especially trying to work on solving our serious flooding problems because most of the land is a drainage for hundreds of acres, and we've gotten very tired of panicking whenever it rains hard We're trying to become more resilient in the face of this challenge which is only going to become greater in this region. We want to hold more water in the soil, while letting it drain naturally to the creek and on down to the river.

Threads about some of our projects:

http://www.permies.com/t/53556/earthworks/Creek-repair-rock-dams

http://www.permies.com/t/51421/earthworks/Creek-repair-brush-dams
 
Ross Mars
Author
Posts: 9
Location: Perth
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One of the key fundamentals of permaculture is "Design for Catastrophe". As our climate is changing, two things will be evident. Firstly, some areas of the world will become more wet and others drier. Secondly, there will be extremes of weather, so more flash floods, more droughts or extremes of temperature. We all need to become better designers to enable our properties to become resilient in the face of adversity. My permaculture 'specialty' is water - how to harvest it, use it, store it, recycle it, conserve it and move it. Having excess water can be a blessing if you can get into the ground or storage tanks or dams, or at least have provision to drain excess away. I don't have quick fix answers for a deluge from nature, but think about how you could mitigate these events should they occur.
 
Tyler Ludens
pollinator
Posts: 9740
Location: Central Texas USA Latitude 30 Zone 8
180
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Ross, I'm hoping you can advise me about a plan or scheme I have for constructing a permanent dam (pond) on our periodically flooding land. There is typically no live water on the place, but during heavy rain we get drainage from hundreds of acres. Average annual rainfall is supposed to be about 28 inches, but in reality it varies from about 15 to about 40.

Here is a map of our 20 acres showing placement of some rain harvesting features and drainage patterns. "Future pond" indicates where I'd like to put a small pond (very small; 1000 square feet surface area or less). Do you think a permanent pond is plausible under these conditions?

 
Ross Mars
Author
Posts: 9
Location: Perth
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Tyler, I think your dam is too small. In a heavy rainfall event of one inch over your 20 acres, about half-a-million gallons fall. Imagine what falls and moves towards your place from the much larger catchment/neigbouring properties. A 1000 sq ft dam which is say 6 feet deep only holds 45,000 gallons. Assuming most water that falls ends up in soil I would still expect that dam to fill in one heavy rainfall event. You need to think about diverting runoff from neighbours away from your property as best you can, and collecting more water, which needs to take overflow towards creek or to another dam.
 
Tyler Ludens
pollinator
Posts: 9740
Location: Central Texas USA Latitude 30 Zone 8
180
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Thank you, Ross. I see the dam as at the end of a long series of catchments - what I want to know is if you think there will be enough water to fill a small dam - it looks like you think there will be too much!
 
Tyler Ludens
pollinator
Posts: 9740
Location: Central Texas USA Latitude 30 Zone 8
180
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A couple of observations as the flood waters recede - my kitchen garden was damaged by water-logging - many of the plants turned pale and growth slowed way down. Now as the soil dries out they are turning green and growing better. The basin at the top of the property is still full of water and overflowing, and the seasonal creek is still flowing, which indicates to me that we can stand to install a lot more water-slowing and soaking capacity.
 
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