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Groundwater 101

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In this episode we explore how vital groundwater is as a natural resource and discuss what impact a changing climate and human consumption has on groundwater supplies. Join us, as we sit down with USGS Groundwater Specialist Marshall Gannett to get a primer on the role groundwater plays in our daily lives, today on the Oregon Science Podcast.




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[Steven Sobieszczyk]  You are listening to the USGS Oregon Science Podcast for Tuesday, August 2, 2011.

In this episode we explore how vital groundwater is as a natural resource and discuss what impact a changing climate and human consumption has on groundwater supplies. Join us, as we sit down with USGS Groundwater Specialist Marshall Gannett to get a primer on the role groundwater plays in our daily lives, today on the Oregon Science Podcast.

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[Steven Sobieszczyk]  Hello and welcome. I’m Steven Sobieszczyk. Last episode we concluded with a bit of a cliffhanger concerning an upcoming video that would describe a contaminant and habitat study for the lower Columbia River that utilized the electroshocking techniques we featured last time. Lucky for us that follow-up video garnered enough interest that it was actually bumped up from our local Oregon Science Podcast to the national USGS CoreCast podcast. So, if you’re curious about the contaminant and habitat study, or ConHab study, check out the video at the USGS CoreCast website at or just follow the links in our show transcripts.

Today, we are back to discussing groundwater. We are pleased to be joined by the USGS Groundwater Specialist here in Oregon, Marshall Gannett. Thank you for joining us today, Marshall.

[Marshall Gannett]  Pleasure to be here. 

[Steven Sobieszczyk]  For those listening who may not be familiar with the role the USGS has concerning groundwater, can you give us a little background on what the USGS does with groundwater?

[Marshall Gannett]  We do a number of things at a variety of scales, local up to national levels. One of the important things we do is we monitor water levels in wells, which is sort of the key indicator of state or the health of an aquifer system. We also track water use and keep tabs on how much groundwater is being pumped, as best we can. We’re also keeping track of the amount of groundwater discharge coming into those streams. The other major role we have is conducting targeted studies in areas where there is heavy groundwater use or where problems are developing. Those studies are usually designed to answer specific questions that resource managers have to allow them to understand the consequences of their management strategies.    

[Steven Sobieszczyk]  Most people, especially in cities, are probably not very familiar with how vital groundwater is for us. How dependent are we on groundwater?

[Marshall Gannett]  We’re very dependent on groundwater throughout the state. There are really three ways in which groundwater are important. First is as a source of drinking water for municipal water supplies, for household water. Over 60 percent of the people in the state rely on groundwater for drinking water. Communities like Bend, Redmond, Sisters are entirely dependent on groundwater, as is Klamath Falls and a number of communities in the Willamette Valley. We’re also dependent on groundwater for irrigation. There are a lot of basins in the state where that is an important or may be even the primary source of irrigation water. So that’s another big use of groundwater. But another use…another important aspect of groundwater that most people don’t think about is it’s the major source of streamflow throughout much of the year, particularly in the late summer and fall after the snow has melted and the rainy season is over. So groundwater is an important source of streamflow for aquatic ecosystems.

[Steven Sobieszczyk]  What are some challenges people face managing groundwater resources here in Oregon and Pacific Northwest?

[Marshall Gannett]  The big challenge is balancing the amount of water that you pump for human uses…balancing that rate with groundwater that naturally recharges the aquifer system. And the things you have to maintain are stable water levels, in other words, if you pump too much groundwater you start to draw down the water table. And you can do that to the point where you can actually dry out aquifers entirely where they no longer become usable.  

[Steven Sobieszczyk]  So is pumping the primary controlling factor concerning groundwater availability in a specific area?

[Marshall Gannett]  The biggest external influence on groundwater systems is climate. The way we know that and the way we understand that is by relating the fluctuations we observe back to climate cycles. I’m referring to things like the decadal drought cycles that we see. So for the last few decades we’ve had these wet periods and dry periods occurring with some regularity. And the water table goes up and down in response to those. It might go up and down a few feet, but in some areas, like the Cascades it can go up and down 20 or 30 feet in response to those drought cycles.  

[Steven Sobieszczyk]  If climate is the main factor for groundwater resources, what type of changes will we expect to see to groundwater as our climate continues to change?

[Marshall Gannett]  There’s really two parts to that question. One is “what do we know about future climate conditions?” And the main consensus is warming and that is going to have a big effect on snow hydrology. And in particular, the timing of runoff and the timing of groundwater recharge. The other aspect where there’s more uncertainty is “what’s the total precipitation going to do?” Is it going to go up or is it going to go down? Or is it going to kind of stay the same? And that’s not known with a lot of certainty. So we can look at the historic response of groundwater systems to the natural climate cycles we’ve seen in the past where we look at a range of possible future climate conditions and then using our knowledge we gain from looking at past behavior of hydrologic systems sort of try and anticipate how groundwater and surface water systems are going to respond in the future. The projected warming and changes in snow hydrology are expected to change the timing of groundwater discharge to streams and springs. Not only are the streams in the future potentially going to have smaller late season flows because of the shifting and timing of snowmelt and runoff, but the timing of groundwater discharge to those streams will shift to earlier in the year, as well. 

[Steven Sobieszczyk]  Well, Marshall, that’s all the time we have for this episode, thank you so much for joining us?

[Marshall Gannett]  My pleasure.

[Steven Sobieszczyk]  Thanks for listening. If you want to learn more about groundwater resources here in Oregon, you can find links to more resources listed in our show transcripts. You can find them at our website: If our podcast doesn’t feed your need for USGS-related news, you can stay abreast of other USGS activities, research, and the like daily on Twitter at “USGS_OR.” As always, if you have any questions, comments, or even complaints about the USGS Oregon Science Podcast, please feel free to email us at  Until next time, I’m Steven Sobieszczyk.

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This podcast is a product of the U.S. Geological Survey, Department of the Interior. 

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