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Sunday, June 3, 2012

Swales


Connect the dots: Signs of Global warming are being seen all over Earth
Sea level rise
•Drying....Lakes have disappeared. Wells and springs drying
Heat waves
Cold snaps
Floods
Tornadoes and cyclones
Fires…intensity & frequency
Snow seasons failing
Glacial melt

In the South West of Western Australia a drying climate is leading to noticeable lower productivity. The sun is more intense leading (in our garden at least) sunburn on harvested onions and garlic, berries, capsicums  etc. It is much hotter , dryer and more humid in the last 5 years. We've been here for nearly 29 years with our hands in the soil most days.
  Soil erosion occurs when grass cover is sparse and rain events are so spread out....soil is lost when isolated rain events or wind dislodges dry uncovered soil. Deserts are growing globally. 75 billions of tons of topsoil are lost from the arable lands of Earth annually. In many places the old people now live in arid zones with little vegetation , but remember trees and their fruits and nuts of the district.  However SWALES (  dead level ditches on contour ) slow and sink the water. They can green the  desert and we must install them over vast areas. They harvest rain and make a deep wet zone where trees can establish .
Swales    
For Erosion control, Water harvesting, tree establishment.
OF course Trees are vital to a safe climate in the following ways: 

.Carbon sequestration ….occurs when trees are actively growing .
Shade, shelter, windbreak…
Habitat and protection  for birds, insects, mammals   Such biodiversity is biological pest control. Plagues are reduced.
Trees  cycle water :    transpiring  moisture  during the day  and condensing moisture on their leaves at night. They also provide  organic particles which seed clouds to make rain. Belts of trees on ridges are responsible for orographic rain due to the "lift" of the clouds up over them.. And more. Forty percent of rainfall is due to forests. Clear the forest and rainfall will reduce by 40 %. This effect will be fairly immediate. Though it takes much longer to put trees back they will increase precipitation dramatically once established. Obviously we need to get tough survivors of the tree world in the ground without delay in the current climate emergency.
Mulch/litter/  collector.  
This soil cover= carbon rich humus
 formation=  for every 1 % rise in carbon
 level , a soil it will have 4 times more water-holding capacity!! 
Rehydration of  the landscape 
( fungi / root mass/above ground biomass, soil biota are all mostly water)
Permanent Springs  and Creeks flow once more
Productivity through cash crops  eg fruit /nuts/animal products (extra fodder) / timber sales 


If you live in an area with only a 600 mm a year average rain fall, that means on every square meter of earth,  600 litres of rain will fall in an average year. That is the equivalent of  3 of those blue 200 litre drums full of water for each meter square!!   But sadly hardly any of that water gets into the soil. As with irrigation , most water runs off to the sea.
In the wonderful words of Bill Mollison

" In most countries 80% of rainfall runs off or evaporates. Thus only 12% is available for agriculture or domestic needs. We must legislate for the construction of thousands of miles of swales on farms, as large contour ditches that fill in every heavy rain (more than 10mm/day). In 3 to 6 hours, such water soaks in, and is immune to evaporation or run off. This water , over years and centuries, feeds tree roots, springs and valley streams. Swales enable forests, and forests are both passive condenses of night air, and active cloud generators or rainfall. If we clear the ridges, 40% of orographic rain ceases. If we clear the plains, most condensation and clouds fail to form. Thus, swales precede forests. Forests precede precipitation."

This is the swale we dug in March 2010, after a few months. Even though 2010 had  a half average rainfall, the grass in the swale grew twice as high as surrounding grass. We have found trees we planted in  and on either side of the swale have grown very well with hardly any irrigation. The trees will soon contribute shade, transpiration, leaf litter, habitat and thus manure of birds, insects and mammals. . 
To install swales you have to mark out contour lines. Stew dug these  with a tractor, leaving a soft mound of earth on the contour line. The contour of the land is a line which joins all  points of equal height above sea level. Every point on the marked line of 100 m 


elevation  on a contour map is 100 m above mean sea level.        I.e. A swale is dead level .  Water is simply held in the swale till it infiltrates the soil. This may take half an hour or a few days depending on soil type. It has no choice but to  enter the soil . Photo at left is of 5 recently installed swales at Merri Bee Organic Farm.  During isolated rain events  55 tonnes of water  enter the landscape through these swales as opposed to running off  to the Blackwood river and escaping to the sea. Instead of flood and drought scenarios, swales and attendant vegetation mean year round water in the environment. This is how Mother Earth likes it. 



 Unlike a swale,  a DRAIN  directs water and causes it to flow ( into a dam for instance)because it  has a slight fall, usually 1 : 1000 ( eg. drops one meter of a distance of 1000 meters. ) You can see contour lines on Google maps .  Type in an address, then choose the terrain option when in map  (not  Satellite). Sometimes you have to zoom out or in to get terrain.
Here's the swales 6 months later in September. Fabulous growth which will be mown down and to make mulch around the tiny trees we have planted. Really Cool. Cows will graze the 18 meter strip of grass between  swales. An  electric wire will keep them off the trees. Will have to move them daily but the soil improvement and their happiness will be worth it. 

Into our 7 month without meaningful rain, and heatwaves from November on, and the swales aren't looking too bad.
Here is a list of stock fodder trees we have planted on swales : . So  acacias and tagasastes  are interspersed with the long term trees. Fodder species include tagasaste, bamboo, carob, oak, sheoak, comfrey, saltbush, honeysuckle, coprosma, willow, poplar, ash, mulberry, grape, fig, apple, stone fruit, ivy, kurrajongs ACACIA microbotrya ( Manna wattle) Mulga ( acacia Aneura) ACACIA saligna , Wilga (Geijera parviflora,) Belts of trees not only provide high quality browse but shade and shelter, salinity and erosion control, clean air and water in the landscape . Oh and timber trees might be handy in the future too.

 

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