Dec. 4, 2007
Thousands of miles of land is being lost to advancing deserts each year. That coupled with the exponential population growth does not bode well for the planet and the people and animals and plants that inhabit it.
The loss of plants and the advance of the desert creates a snowball effect. Without vegetation the rain that falls does more harm than good, creating floods and washing valuable top soil away.
The rains and flooding in and of themselves create more desert by washing the existing plants away.
The advance of the desert is more pronounced nearer the equator.
Nowhere is this more evident than in Africa. Africa’s top soil is actually being blown all the way to South America.
The larger the population, the more rapid the advance of the desert.
The temperature increases forecast due to global warming only indicate that millions of more acres of vegetation will be lost.
This leads to more global warming, more erosion and faster advance of the desert.
People are already starving to death in Africa, and it seems that matters will only get worse unless something is done.
Archaeologists have named an ancient no longer existing culture that lived in pit houses in the desert Southwest of Arizona the Hohokum.
The Hohokum were hydrological engineers, growing large quantities of crops in a totally arid area.
They didn’t dig deep wells, nor did they have the machinery to build huge dams to capture the somewhat seasonal and mostly sporadic rains.
What the Hohokum did was develop a simple technology that allowed them to harvest the limited rain that fell.
The technology they developed is labor intensive, but free of the need of tools except for the occasional use of a digging stick.
The Hohokum were the original innovators of the check dam, the gavion and the swale.
Little if any land on the planet is totally flat, and when rain falls on the ground it runs in one direction or another and creates rivulets, gullies, washes, arroyos, creeks, streams and rivers.
A large part of the water that falls on the planet eventually makes its way to the ocean if it is not stopped and used by plants or if it does not slowly seep and percolate into the aquifer.
In the desert where the Hohokum lived most of the rain when it came, came down intensely and rapidly, washing out into the desert and evaporating, without it ever having a chance to really penetrate into the soil.
By placing small little dams of piled rocks (check dams), the Hohokum were able to slow the water down enough so that it penetrated into the soil, and this is were they started growing there crops.
The trick to check dams is not to have large check dams, but to have numerous small check dams one after another.
As the water was captured or slowed down it transformed the area around it as it became saturated with life giving plant growing water.
As plants took over, they captured more and more of the limited rainfall, and the Hohokum built more and more small check dams and expanded their growing area.
Check dams are great for small areas without a great volume of water, but are limited in their ability to slow down areas where a great deal of water is coming down rapidly.
The Hohokum had to come up with something else. They came up with the gavion.
A gavion is basically a large dam of piled loose rocks strategically placed and at first held in place by netting. After the initial flooding, the netting becomes extraneous because the dirt washed through the gavion holds and cements it into place.
A gavion has to be porous and allow water to pass through it. If too much water builds up behind it, it will not be able to hold the tremendous weight back and it will wash out. So, once again, a number of small gavions are indicated rather than a couple of large gavions.
The areas behind the gavions, even in the driest of deserts, are transformed, and luxurious plant life grows and birds and animals come.
The longer the gavions and check dams are in place, the greater the transformation of the surrounding desert as more and more water seeps into the aquifer.
As the aquifer rises, the capillary action of the water slowly rising to the surface greens the surrounding desert.
The Hohokum were not content with just these two innovations, they also developed the swale.
A swale is based on the same premise as a terracing, though it is not nearly so extreme or labor intensive to built.
A swale follows the contour of a hill. An area of approximately one meter is leveled starting about three meters down from the top of the hill. This level area catches the water falling on the top of the hill, allowing for plants and grasses to be gown in the leveled swale area.
Another swale is placed three to five meter below the top swale, collecting the water that falls in the area between the two swales and any water the might escape the upper swale.
This continues down the hill until the area where check dams and gavions take over. This transforms the entire hill and the surrounding area even in the driest of environments.
Southern Arizona is suffering from a severe thirty year drought. All these techniques have been used to great success there.
The author has assisted in building many check dams, gavions and swales and has seen brown and barren hillsides and flatlands become lush and green with vegetation. Each year that he has gone back to check on his handiwork, the vegetation has expanded.
It brings a smile to the author’s face when he sees a stream flowing year round where previous to the check dams placed on it, it only flowed when rains fell.
It is hard physical labor to build these structures, but it is healthy good exercise, and the more people involved the faster it goes.
These simple technologies need to be implemented wherever desert is advancing, and in areas that have already turned to desert. This is especially true where there is manpower to do the work.
These ancient tried and true hydrological systems seem to be one of the few viable alternatives to avoid widespread starvation and famine.