storage

A cleansing flood for the South Fork in 2011?

It’s still the middle of winter and lots more snow needs to pile up in the mountains, but early indications are the snowpack is average or better, but more importantly there is A LOT of water in Anderson Ranch Reservoir.  And it’s got to come downstream at some point in 2011.

So for our first update for 2011 we present a state of the river report, looking at the coming water year.  Long time South Fork Boise aficionados recall the normal flow regime is 300 cfs in the winter (Oct through March), followed by the 600 cfs for the shoulder season, usually a period in September but also importantly in April and May for the mainstem river spawning.  Then during the summer it’s around 1,800 cfs in a steady push of water for downstream irrigation and salmon water budget contributions.

This year looks like it will be different because the water is stacking up, more than in recent years.  Here’s what we know so far…

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Summer 2010 flow assessment

Today the flows at Anderson Ranch Dam were decreased by 200 cfs to the summer “normal” flow of 1,600 cfs (first graph).  The salmon flow augmentation releases concluded July 15.
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Trinity snowpack hangs on, then same ending

Finally some summer temperatures in southwest Idaho!

After the cool, wet May and (most of) June, the summer weather pattern is starting to take hold and the last of the mountain snow is making it way to feed Idaho’s great rivers. And on this blog we watch the upper South Fork Boise River has it has the heavy influence on the releases from Anderson Ranch Dam and the blue ribbon trout stream.

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Cold, wet mid May = more water later

Last weekend snow blanketed the Boise Front with 16 inches recorded at Bogus Basin.  Trinity Mountain in the Upper South Fork Boise River picked up about four inches, but it’s the cool weather before and after that has kept more water stored in the mountain snow than in Anderson Ranch Reservoir.

The flows from Anderson Ranch were increased to 1,600 cfs during the week to help meet irrigation demand and this appears to have stopped the filling of Anderson Ranch because there is little snow melt in the high country.
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A Look to the Upper South Fork Boise

A couple of warm days signals the beginning of spring run-off.  And a set of charts assembeld above provides insight on what the near term holds for Anderson Ranch Reservoir.  And there are implications for the South Fork Boise downstream of Anderson Ranch Dam.

The first chart shows the inflow to Anderson Reservoir at Featherville.  The flows have started to increase and are converging towards the long term average.
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