Sunday, April 29, 2012

Water World

We live on the Blue Marble Planet - an Earth that is more than 70% covered by water, both salt and fresh. What isn’t covered by water frequently is covered by clouds - just another form of water.
I have a question about water use in the US for a science project. Do you do water science?
– (no name given)

Water figures everywhere, throughout all our lives. With the burgeoning human population, however, potable water is becoming an ever more precious commodity across this planet - and less than half the human population has access to it.  People eat, drink, poop, and sleep - so how do you separate the middle two?

The US Geological Survey has an entire Discipline devoted to water science. There are a number of sub-headings under water science including surface water, groundwater, floods and droughts, and water quality (water pollution - separating the drink from the poop). Several people in my office, for instance, have the word “Hydrologist” below the names on their wall-plaques. Hydrology is one of the major sub-fields of Geoscience, along with geochemistry, geophysics, geology, mineralogy, etc... but in truth, good water science - modern water science - crosses all those boundaries.

Things like surface water, floods, and droughts are pretty obvious: you can “touch” and “see” these without instrumentation, and most people have some personal experience with each. If you don’t know what’s about to come down your river, you can’t prepare for the flood when it DOES come. That’s part of what surface water science is about: recording, tracking – even predicting. Water quality/pollution studies require laboratory testing, sometimes involving chemistry, sometimes involving electronic equipment. Sometimes it involves biological testing, too. But your nose can tell you some of it: Eewww! Don’t drink that.

Ground water, on the other hand, is hard to put your finger on - figuratively and literally. To do this, you must drill a LOT of holes, and ultimately, you must delve into the geophysics domain. Electrical geophysical methods are routinely used to search for changes in underground conductivity. Well logs – instruments lowered down boreholes - measure it vertically, but in just one place. Airborne electromagnetic systems measure it as they fly over – I recently published a US Geological Survey Professional Paper showing how you can do that (to see the water in 3D, discussed in a later chapter). The greater the conductivity, the more water is present; this assumes that the water has a relatively uniform amount of dissolved solids in it. This will tell you where the water is, but not where it is going. That takes extra work, including measuring, pumping, and modeling.

Traditional hydrology involves working with a whole series of wells, measuring the water table and its variations, and conducting pump tests to see how sustainable a given well might be. Testing a well is designed to see if it really “plugs into” a larger zone of at least moderate porosity filled with water – or not.

Yes, there is a lot of water science out there, and yes, we do a lot of it. We’ll drill more into this in the next chapter, but for now this has been a quick summary of water science.


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