Found this great research paper talking about the hydrologic effects of thousands of small check dams on a watershed in Arizona. It compares the treated watershed to an untreated one next to it and comes up with some solid numbers supporting the fact that not only do the check dams mitigate flooding after rain events, they actually increase overall stream output in the long term. Concrete evidence that check dams will increase the amount of water available to people downstream to help alleviate fears that check dams take water away from people downstream.
"Instead of Pay It Forward I prefer Plant It Forward" ~Howard Story / "God has cared for these trees, saved them from drought, disease, avalanches, and a thousand tempests and floods. But he cannot save them from fools." ~John Muir
TO: Michael Newby
FROM: Eric Koperek = email@example.com SUBJECT: Check Dams
DATE: PM 6:47 Thursday 3 Mars 2016
1. Check dams are a simple technology used to develop wadi = gully = canyon = arroyo = coulee dry land agriculture systems.
2. The purpose of a check dam is to SLOW not stop water movement. Slow water drops sediment (sand, silt, clay, and organic matter) which collects behind check dams. Soft sediment acts like a giant sponge to store water between rains.
3. Plant deep rooted drought resistant trees in the collected sediment behind each check dam. The trees thrive because of extra water and fertile soil.
4. This is a type of rain-fed = rain irrigated agriculture = flood irrigation = no human intervention required. Canyon systems collect runoff from vast areas, greatly multiplying the effective rainfall in the canyon. A typical wadi system collects 10 to 20 times the average yearly rainfall for the region. (For example, 1 inch of rain in the uplands = 10 inches of rain in a wadi). This is because most of the rain runs off the high lands and drains into the canyons. Thus, in any desert or semi-arid climate, the best place to grow crops is in the nearest canyon, no matter how unpromising it may appear.
5. For best results, start as far up the canyon system as possible. Up = upstream. The idea is to control the water BEFORE it becomes raging torrents and floods. Build check dams all the way down the wadi, including all subsidiary = tributary canyons. Build a check dam every 50 to 100 yards depending on how much rock it is easy to collect. Check dams can be spaced closer together where grades are steeper.
6. Rule-of-Thumb: The crest of the next downstream check dam should be the same elevation as the toe of the immediate upstream check dam. Use this simple rule to efficiently space check dams. The idea is to have check dams close enough together so that flood waters never reach high velocity. Fast water is dangerous and hard to control. Slow water is much easier to control.
7. Check dams are easy to construct: Simply dump baskets of stones on the ground until dam reaches 3 feet high. Stones should be as large as it is comfortable to pick up with both hands. (Small stones will just get washed away). Think "rip-rap" = grapefruit to melon sized rocks.
8. In wadis with substantial water flow check dams should be "keyed" into the sides and bottom of the wadi. Cut 3 feet deep into each bank and 2 feet deep into the stream bed then dump rocks to build dam. Make the center of the check dam about 6 or 8 inches lower than the sides. In cross section, your check dam will be slightly curved like a banana. The lower middle part of the check dam acts like a spill way to prevent high waters from washing out the check dam.
9. You can also use "gabions" to build check dams. Historically, gabions were large, hollow tubes made out of wicker or brush, similar to large harvest baskets without bottoms. Stack up gabions and fill with rocks. Modern gabions are crates made from industrial strength chicken wire. Each gabion is about the size of a 40 pound square hay bale or a bale of peat moss. Fill each gabion with stones then wire the gabion tightly shut. Gabions enable you to build check dams using small stones that would otherwise wash away. Orange-sized rocks are ideal for filling wire gabions.
10. Ideal trees for wadi agriculture include: Date palms, Dom palms (and other forage palms with fruits & seeds used to feed camels & other livestock), Olives, Almonds, Pistachios, Walnuts, Cork Oaks, Apricots, Peaches, Frankincense, Myrrh, Tamarisk and other various species of fire wood trees. Ideal wadi crops include melons and other vine crops, barley, and wheat.
11. It is good practice to build "waffle gardens" in the uplands at the same time that you build check dams in the canyons. Waffle gardens are made by dumping baskets of stones along contour elevation lines to make low walls = bunds about 6 to 8 inches high. Any kind or size of stone can be used. Make each box 5 to 50 yards square. From the air, the boxes of rocks look like waffles, hence the name. Each little curb or line of rocks slows both water flow and air speed across the land. Favorable micro-climates are created within each box = waffle because wind and water erosion are reduced = plants have more humidity and soil moisture. The idea is trap rainfall before it runs off the land into the wadis. More water infiltration = re-charged aquifers = higher water tables = local villages have plentiful water in their wells.
12. If you have access to a small backhoe or trenching machine you can dig narrow, horizontal trenches across the wadi floors to intercept floods as they race down the canyon system. Make the trenches as deep as machines will dig and 4 to 12 inches wide. The trenches will channel vast amounts of water into the subsoil and will also trap significant quantities of sediment into which you can plant deep rooted crops.
11. For more information on old-fashioned "biological" agriculture please visit: www.agriculturesolutions.wordpress.com --or-- send an e-mail to: firstname.lastname@example.org
For more information about old-fashioned biological agriculture please visit: www.agriculturesolutions.wordpress.com -or- www.worldagriculturesolutions.com -or- send your questions to: Agriculture Solutions, 413 Cedar Drive, Moon Township, Pennsylvania, 15108 USA -- or -- send an e-mail to: Eric Koperek = email@example.com
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