Water, water everywhere
Now be honest with me. You could find few topics of less interest to you than the study of water that lives an honest life in the pores between grains of dirt beneath your feet. Am I right? I mean, what possible interest could attach to the study of stagnant underground H2O? Well, let me give you a piece of advice; unless you have a strange fondness for being sternly lectured, don't ever tell a hydrologist how you feel. These good folks who make a living from their knowledge of subterranean water will assure you that nothing else on this planet has the same degree of charm and fascination as interstitial wet stuff. After all, it not only provides crucial services to the world economy it also is the home of untold thousands of species of amazing creatures - bacteria, protozoa, nematodes, rotifers, tardigrades, algae, and "worms" of myriad shapes and sizes - found nowhere else. And believe it or not, scientists continue to make completely unexpected discoveries about the stuff. Which should come as no surprise to those who recognize the wisdom of God in every nook and cranny, literally, of creation.
Most of us never give groundwater a thought until it starts to dry up, as is currently occurring in parts of America's vegetable bowl, California's Central Valley. Since 2003 the region's aquifers have lost enough water to fill Lake Mead, America's largest reservoir. Continued drought and increased pumping of the water for irrigation is steadily sucking the soil's pores dry. Some orchards have already begun to wither (see pic top right) as the water table drops below root level. The drop not only affects agriculture but even the land itself as subsidence begins to occur. Doors won't close, windows won't open; not a heartening thought for those who live there.
A few fundamental facts won't go astray. Did you know that, although groundwater makes up only about 1% of the total amount of water on earth (most of which is in the oceans), it nevertheless amounts to about 35 times the volume of water in lakes and streams? Pump every drop out of the ground and you would flood the entire surface of the earth to a depth of 55 metres. Groundwater is found everywhere, but, obviously, is more abundant in some locations than others depending on the underlying and surrounding geology and precipitation levels. The Central Valley of California has a couple of extensive aquifers fed by rain and snow that falls on the nearby Sierra Nevada mountains. Some of the rain and snow drains away rapidly in streams and rivers, but a portion soaks into the soil and then flows underground at varying speeds (governed largely by the porosity of the ground) by percolating - under the influence of gravity - through the tiny spaces separating soil particles. Exactly where it exits (discharges) the ground - in a spring, into a river, or directly into the sea - depends on all sorts of factors. Some sinks into the underground equivalent of a lake where it can sit for many
thousands or even millions of years as "fossil water". Unlike surface water, groundwater can flow "uphill" under conditions where higher pressure lower down pushes it upwards to zones of lower pressure.
Now here's an amazing thought. Because the direction of flow of groundwater depends on the lie of the impervious rocks over which it flows under the influence of gravity, it can flow in a different direction from the overlying rivers and streams whose movements are dictated by surface topography. A river can be flowing north while the groundwater beneath it can be flowing east or west! If you think that's cool, be prepared for a real shock. Groundwater can cross rivers! Yes, it can. Even when the impervious rock beneath groundwater comes right up close to the bed of a river so that the groundwater cannot flow beneath the river it can still cross it. In 2007, researchers at the University of Granada discovered that, "contrary to popular belief, rivers do not act as insurmountable barriers for groundwater flow":
The analysis of piezometric, hydrochemical and isotopic data from groundwater flows revealed that they cross the Guadalbullón River from one bank to the other due to a certain geological structure which prevents the groundwater from being influenced by the river flow. The analysis of all this information has made it possible to create a new hydrogeological model which explains most of the current mysteries.
Now I don't really understand that any better than you do. But I gather that it means that groundwater can continue on its merry way westward, say, after crossing a north-flowing river. Let's give God the credit for thinking such marvels through. Though this apparent mystery has been explained, others await future elucidation.
As announced only a few weeks ago, yet another discovery challenges "a century of assumptions about soil hydrology". According to one report,
Researchers have discovered that some of the most fundamental assumptions about how water moves through soil in a seasonally dry climate such as the Pacific Northwest are incorrect - and that a century of research based on those assumptions will have to be reconsidered. The finding is so significant, researchers said, that they aren't even sure yet what it may mean.
They have discovered that, contrary to previous beliefs, rain that falls after a prolonged dry spell becomes so tightly bound to the soil that it stays in place even after later rain washes through. Amazing? You bet. As the psalmist put it,
Who can utter the mighty acts of the Lord? Who can declare all His praise ?