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Home » Santa Clarita News » Environment » SCV Outdoor Report » SCV Outdoor Report: Hydrogeology for Dummies – pt 3.

SCV Outdoor Report: Hydrogeology for Dummies – pt 3.

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By Wendy Langhans

Quick – how many states are in the continental United States?  If you said 48, you’re right.  Now – how many watersheds are in the continental United States?  Would you believe me if I said more than 2,000?

This is the last in our 3-part series on hydrogeology.  Today, I’m going to give you 3 keys for understanding the directional flow of ground-water.  The first key is the watershed.  According to the EPA, “A watershed is the area of land where all of the water that is under it or drains off of it goes into the same place.”  Our Santa Clara River watershed drains into the Pacific Ocean.  Here’s a link to our watershed, showing the surface drainage patterns.

Piru_creek

But what things look like on the surface can be deceiving. We need to dig deeper to better understand the directional flow of groundwater.

The second key to understanding the flow of groundwater is to look at underlying 3-dimentional rock structures, including the groundwater basins.  Just remember, as a general rule, that “stuff flows downhill”, even though it may thousands of years for groundwater to get where it’s going.  Here’s a link to the underlying rock structure and another link to our local, eastern Santa Clara River Valley groundwater subbasin (see page 8).

As we learned last week, rock formations differ in their porosity, the percentage of open space between the grains and in the cracks and fractures.  Not only will groundwater flow downhill through porous and permeable rocks, but also through cracks in an otherwise impervious rock.

 


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There are two major aquifers in our eastern Santa Clara River ground-water basin:  the the Alluvial aquifer and the Saugus Formation aquifer.  The Alluvial aquifer, which consists of “sand, gravel, silt, and clay with cobbles and boulders”, lies mostly beneath the chanel of the Santa Clara River.  The Saugus Formation looks like a series of nested bowls and consists of “sandstone, siltstone, and conglomerate”.  These aquifers flow in an east-to-west direction and are source of water for irrigation and municipal use.  Here’s a link to a sketch of the aquifers.

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The third key has to do with how human activities can change the direction of groundwater flow.  If you pump water from an aquifer, you may change the shape of the water table, creating a funnel-like “cone of depression”.  Ground-water will will flow into this cone, just like liquid flows into a funnel.  To see how this works, here’s a link to an animation.  This means that, from the perspective of an observer on the surface, groundwater could actually flow uphill, at least for awhile.  As I said earlier, what things look like on the surface can be deceiving.

Thanks for joining me in this brief (and shallow) glimpse into hydrogeology.  I hope it has given you the information and tools you need to follow some of the water-quality discussions in our Santa Clarita valley.  Just to put it in perspective, in California, there are 58 counties – but 190 watersheds.  And size-wise, LA County is one of our nation’s largest counties – 4,084 square miles.  But our Santa Clara River watershed drains 1,634 square miles – that 40% of the size of LA County.

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Upcoming Outdoor Events:

Saturday, September 10th, 5:00 – 7:00 PM, Changing Seasons Evening Stroll at Towsley Canyon.  With summer on the waning edge, this is a great time to explore the park and see what seasonal changes occur as we move into fall. You’d be surprised how the flora and fauna cope with our summers and prepare for their upcoming rainy season. Easy walk, 2 hours. Meet at Towsley Canyon’s front parking lot.  For directions and trail maps, click here.

Trail Maintenance Schedule.  Come join our volunteers as they help maintain our trails.  Contact Steve at machiamist@aol.com for time and place.

Wednesday mornings, August 3, 10, 17, 24, & 31.

Saturday mornings, August 13 & 27.

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You can listen to stories like this every Friday morning at 7:10 a.m. on “The SCV Outdoor Report”, brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.

You can listen to stories like this every Friday morning at 7:10 a.m. on “The SCV Outdoor Report”, brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.

SCV Outdoor Report: Hydrogeology for Dummies – pt 3.

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