South Fork Boise River flows downstream of Anderson Ranch Dam
The Bureau of Reclamation began turning down the dial on the boating flows after the end of the Labor Day weekend.
By the end of Tuesday September 4th flows dropped from 1,850 cfs to 900 cfs. On Wednesday the 5th the flows were at 600 cfs.
Summer boating flows lasted longer and were slightly higher than the typical 1,600 cfs. In fact, the 1,800 cfs flow seems to be a “new normal.”
So why did flows stay higher through Labor Day? Continue Reading…
It certainly was a long, bleak December and early January, especially if you ski at Bogus Basin. The drive into the South Fork canyon was less treacherous. In the past few days a wave of Pacific storms finally arrived and dumped snow across western and central Idaho. Here’s a chart showing snowpack so far this year compared to the three previous years:
So what does this mean for flows this summer?
We are holding steady at 2,000 cfs from Anderson Ranch Dam. Anderson Reservoir is now 98 percent full and should top off in the next week.
The slow, steady melt this year has been rather amazing. Despite a dry 2010 water was saved and we entered 2011 with reservoir contents in pretty good shape. Lots of snow this year, but a slow melt, has meant the pools are filling slowly in May and June. Today the pool finally fills to the point to equal that of last year. But this year it is still filling and in 2010 by the first week of July the reservoir was starting to drop. Check out the chart -
Indications point to ending the year with more water than a year ago. And 2010 was slightly higher than average.
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…
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.
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.
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.
It’s a water short year measured by snow in the mountains, but Anderson Ranch Reservoir has more water stored than last year.