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The Backyard Science group regularly features the Daily Bucket.  We hope you will add your own observations of the world around you.  Bees buzzing?  Sun shining? Aphids on the roses?  Please tell us about it. Insects, weather, meteorites, climate, birds,  and more are all worthy additions to the Bucket.  Please let us know what is going on around you in a comment.  Include, as close as is comfortable for you, your location. Your impressions support our understanding of the mysterious cycles of life that are quietly evolving around us.
Often, very young, and very old rivers meander in  shapes like coiled snakes.  The river may wander for 100 miles, but only move 50 miles in a direction.  Sometimes rivers double back on themselves so severely, that they cut new channels, and leave a curved portion of the old channel behind.

 The abandoned channel is called an oxbow lake.  Many rivers have spawned oxbow lakes that provide popular recreation spots, safe from a river’s often dangerous currents.

The flip side of an oxbow lake is an unnatural and harmful phenomena, called “pit capture.”  Gravel miners have to dig their pits where the gravel is, and it’s often easily found, and cheaply obtained from the old river channel, right next to the current river channel.

This means that too-many gravel mines and their multi-acre pits, often deeper than the river bottom, are located within a few yards of a river.

 Indifferent miners, and uncaring regulatory agencies sometimes don’t account for nature’s forces.  In wet years, the rivers can overflow, smash down the dirt berm between the river and the gravel mine, and fill the pit with flood water.  The river has “captured” the pit.  An abandoned, or uneconomic pit, simply becomes a backwater on the river.  Sometimes the miner can pump out the pit and resume mining.

Pit capture changes the river’s whole routine.  The river roils as it flows into the deeper pit.  That’s called the nickpoint.  The water’s action causes the river bottom to erode, and the erosion moves upstream.  That’s called incision.  Sometimes incision from pit capture can cause a river to undermine highway bridges that were miles upstream from the captured pit.

If the river harbors a warm-water fishery, of bass, carp, and panfish, pit capture is harmful, but not the end of the world, although it does divert a portion of the river’s flow, and change the river’s channel and characteristics.

However, if the river provides a cold water fishery for salmon, trout, or similar species, the captured pit saps the life in the river.  Warm water predator fish like bass, and bullfrogs seek shelter and breeding grounds within the former pit.  Their population grows.  Then they periodically sally forth from their “safe house,” and raid the river, devouring the spawn and young of the cold water fishes and amphibians.

Salmon spawning in central California’s Merced River, which drains the majestic Yosemite Valley, must struggle their way past at least 15 captured gravel pits. State agencies often have to spend millions of dollars to rebuild berms and restore habitat, to preserve cold water fisheries threatened by pit capture.

 Please keep these issues in mind, when you are enjoying a stroll by your favorite river, and hear bulldozers and backhoes extracting gravel nearby.

And now it’s your turn to tell us what’s new in the natural world.  Hopefully the only pits are from your ripened peaches.

Originally posted to Backyard Science on Sat Jul 20, 2013 at 06:55 AM PDT.

Also republished by Badger State Progressive and Community Spotlight.

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