design info for swales

Apr 23, 2011 21:44:33

Hello everyone

I am looking for recommendations for books or other sources that set out general rules of thumb for creating swales.

I have 160 acres, sloping south down to the river. It has a half mile of slope with a range in elevation
of 1650 ft above sea level to 1511 ft above sea level.

My questions are general, such as
How much elevation change from swale to swale?
How high is the crest of the swale?
How deep is the trough of the swale?
How wide is the crest?
How wide is the trough?
Is the swale perfectly level or on a slight angle to compensate for plant growth in the swale.(plant growth will change the ability of water to flow in the swale. It is a restriction on flow)
What are the factors that change these diamentions?

If these questions have been answered in another thread, please direct me to it.

Thanks saskrr

Apr 24, 2011 11:50:12

I am new to the philosophy of swales, so I will let somebody else give specific information. Some more information could be very helpful though:

* Is this land heavily forested? Prairie?
* Do you have a good ground cover?
* Soil depth?
* Amount, and seasonality of rainfall/year?
* What is your ultimate goal? ie, Ponds, terraces, food forest, etc?

Your slope is fairly steep (I figure about 1 foot elev. per 20 feet). If it is not forested, with a good ground cover, more than half of your rains are probably ending up in the river (along with some of your soil!).

Figures I have heard recommend swales every 15-20 feet. For utility swales 1½ feet deep by 1 foot wide, with a slight slope from one end to the other.

I'm sure that someone more versed in swales will step in and give more specific information, as well as some good reference books.
Good luck!

Apr 24, 2011 13:33:58

A very good book for water harvesting earthworks is "Rainwater Harvesting for Drylands Volume 2" by Brad Lancaster. He describes in detail various kinds of basins, swales, dams, etc (not just for dry climates).

http://www.harvestingrainwater.com/books/volume2/

Apr 24, 2011 18:21:12

Thanks for your response

Now to answer your questions

Trees only at the edge of the river.

The steep 80 acres ground cover is still the original prairie grass enjoyed by Bison for the last 10,000 years.

The more level 80 acres is rented out and has a wheat, canola and field peas rotation.

Soil depth is 18-24 inches.

Rain fall is variable from 3 inches to 25inches (25 inches last summer) see flood video from last year
http://www.youtube.com/watch?v=WQLBxVoQRP0

We are about 600 miles north of tropical montana so our winters are cold and crops choice is limited. I would be happy to slow down the water flow and catch enough to grow some fruit trees and graze animals on a lush pasture.

Apr 25, 2011 01:12:28

Swales certainly sound like the way for you to go. In years with 3" rain, you'll want to keep ALL of it, and with floods like that Youtube link, you'll certainly want to slow it down to retain your soil. Native prairie grasses are pretty good in holding soil. If you can retain all/most of the water, winters will be your biggest limitation (forget bananas).

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