Dawn of the Dead Watershed

Richard (Rick) Mills

Ahead of the Herd

Page 1 of 4

As a general rule, the most successful man in life is the man who has the best information

There’s a lot of water on the planet we inhabit – an estimated 326 million trillion gallons or 1,260,000,000,000,000,000,000 liters.

That makes it hard to believe that there are somewhere between 780 million to one billion people without basic and reliable water supplies and that more than two billion people lack the requirements for basic sanitation.

Harder still to believe are reports water is going to get much dearer in our near term future yet global demand for fresh water may outstrip supply by as much as 40 per cent in 20 years if current fresh-water consumption trends continue.

Our planet is 70 percent covered in ocean, ninety-eight percent of the world’s water is in the oceans – which makes it unfit for drinking or irrigation because of salt.

Just two percent of the world’s water is fresh, but the vast majority of our fresh water, 1.6 percent, is in its frozen state and locked up in the polar ice caps and glaciers.

Our available freshwater (.396 percent of total supply) is found underground in aquifers and wells (0.36 percent) and the rest of our readily available fresh water, 0.036 percent, is found in lakes and rivers.

Aquifers

Freshwater aquifers are one of the most important natural resources in the world today. These underground reservoirs are essential to life on this planet. They sustain streams, wetlands, and ecosystems and they resist land subsidence and salt water intrusion into our fresh water supplies.

Many people think of aquifers as underground lakes but that’s not the case – the water is held between rock particles. Water infiltrates into the soil through pores and cracks until it reaches what is called the zone of saturation – all of the spaces between the rocks are filled with water, not air.

This zone of saturation occurs because water infiltrating the soil reaches an impermeable layer of rocks it can’t soak through.

 Water held in aquifers is known as groundwater. The water table is located at the top of the zone of saturation.

Groundwater represents about 30 percent of the available fresh water on the planet – surface water accounts for less than one percent. The rest is locked up in glaciers or the polar ice caps.

Almost all of the planet’s liquid fresh water is stored in aquifers. Some of the largest cities in the developing world – Jakarta, Dhaka, Lima, and Mexico City – depend on aquifers for almost all their water.

Most rural areas pump groundwater from wells drilled into an aquifer.

There are two types of aquifers: replenishable (a permeable layer of rock above the water table and an impermeable one beneath it) and non-replenishable (also known as fossil aquifers, no recharge) aquifers. Most of the aquifers in India and the shallow aquifer under the North China Plain are replenishable. When these are depleted, the maximum rate of pumping is automatically reduced to the rate of recharge or refill.

For fossil aquifers – such as the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer – depletion brings pumping to an end.

In North America the major concern is over water levels in the Ogallala aquifer under the U.S. Great Plains – the world’s bread basket. The Ogallala is the world’s largest known aquifer having an approximate area of 450,600 square kilometers and stretches from southern South Dakota through parts of Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and northern Texas.

The Ogallala Aquifer was formed roughly 10 million years ago when water flowed onto the plains from retreating glaciers and streams of the Rocky Mountains. The Ogallala is no longer being recharged by the Rockies and precipitation in the region is only 30-60 cm per year.

When groundwater is depleted the effects (besides lessening of supply or no more water) can be drastic. Land subsidence happens when porous formations that once held water collapse resulting in the surface layer settling. Water won’t compress, but when the water is sucked out of an aquifer air fills the void between the rocks where the water use to be. Air compresses and the ground sinks or compacts – the aquifer will never hold the same amount of water again.

One study shows that from 1986 to 1992 some parts of the Mexico City Aquifer’s water levels dropped 6 to 10 meters. Areas of Mexico City, as a consequence, have fallen as much as 8.5 meters. The subsidence (ground compaction) is also damaging the sewer system, potentially leading to untreated sewage mixing with fresh water in the aquifer.