Friday, July 17, 2015

Are Two Weight Belts Enough?

Taking Sediment samples in the Snake River at high flow.  Photo courtesy of Macalester Promotional Material.
This past week we got the opportunity to revisit a previous field site - except during a much higher flow! The first time we went out  the river was flowing around 250 cubic feet per second (cfs, or the volume of water moving through the channel), when we visited this week, it was about 550cfs - this made working in the field quite different. There was a noticeable change in the appearance of the river bed - less fine grained sediment and fewer live mussels!

Taking sediment samples during normal flow! Photo courtesy of Jess Kozarek.
When we collect sediment samples, someone sinks to the bottom and scoops up sediment with a cup - this past time the water movement was much faster - pushing the scooper downstream very quickly. I personally like to use Molly’s legs as a anchor!

As water flux increases, the velocity increases. This higher energy allows for more sediment to move along the bed, or become suspended in the water. This fact was very present at this site in the Snake River. When snorkeling, the visibility had decreased greatly from the last time we were at the site - making it harder to find the mussels.

Yay, cookies! Photo courtesy of Macalester Promotional material.
The mussels we did find were few, and often just shells. Where did all the mussels go that we had found there less than a week before? Had the burrowed deeper? Or traveled with the current downstream? Or could we just not see them?

The hard work was all worth it for some Dan’s homemade cookies!

cfs data found at:

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