It’s that time of year once again.
As a geologist, I’m not thinking of the holiday season when I note this time on the calendar. What’s impressed me lately is the clear start of the annual cycle in which we benefit from a recharging of the nation’s water supply.
In late November, while I was digging my pickup truck out of 14 inches of snow, I had time to meditate on the importance of this time of year. Not long after my shoveling effort, the Midwest was hit by major snowfalls. Now other parts of our geographically complex nation have had substantial rains.
Both snow and rain are different ways of spelling water, of course. Roughly 10 inches of snow are the same as an inch of rain. I say “roughly” because snow can be dry powder, in which case it doesn’t have much water content, or sloppy stuff that weighs a heck of a lot more because it’s got more water in each scoop of my shovel.
Depending on water
There are two basic ways that significant parts of the country will depend on this winter’s snow and rainfall well down the road. That’s worth a moment’s consideration, because we’re just as dependent on water as we are on energy.
First, winter snows at high elevations build up over time. Near the start of the summer, those snows melt. Water enters creeks that flow down into larger streams. That’s why a healthy snowpack at high elevations leads to plentiful water in rivers during the summer. With current climate trends in the western U.S., snowpack runoff may happen earlier in the spring and summer — with important consequences for our ability to generate electricity and meet peak irrigation needs later in the warm season.
But there’s a second, more invisible, way that precipitation is crucial to our water supply. In several regions of the country, aquifers hold water beneath our feet and supply the water that we all depend on.
Here’s the story.
As we all can observe, rain and snowmelt soak into the soil. What we can’t easily see is that part of the water in the soil continues to move downward. It’s a slow process, but over time water trickles into the little cracks and tiny holes that exist in the solid rock that’s beneath the soil.
If you drill a well down through the soil of my backyard and into the rock under it, you’d reach the water table. That’s the depth beneath which water flows into open holes in the Earth, like wells.
Rock doesn’t hold a lot of water. Imagine you could look at some of the rock under my house that’s beneath the water table, a cubic piece of solid stone that was 1 foot on each side. Only a thimbleful of water would flow from that rock into a well.
But a good well gets the benefit of the water that’s stored in huge volumes of rock. And each morning I fill my coffee pot with water exactly like that, what geologists call groundwater from a deep aquifer.
Filling up the aquifers
All aquifers have to be recharged. That’s what is happening at this time of year. Snow and rain are trickling down into soil. Over time, water will move into the rock underneath the soil, recharging the systems on which so much depends.
It’s an unfortunate fact that we are pulling water out of major American aquifers at a faster rate than Mother Nature recharges them. The day will come that we will have to change our way of doing business. It’s not that we abruptly will have no water at all to use, but that we’ll have to engineer more solutions to meet our needs, deal with new environmental impacts and end up spending a lot more money for water than we’re used to doing.
For the New Year, let me raise with you a toast of cold, clear water — an often overlooked but precious gift.
Dr. E. Kirsten Peters was trained as a geologist at Princeton and Harvard. Follow her on the web at rockdoc.wsu.edu and on Twitter @ RockDocWSU. This column is a service of Washington State University.
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