MORE ON THE SNOW AND THE FLOW

It’s the 20th of June, almost summer.  There is more water (frozen) at the Trinity Mountain snow site than there ever was in 2010.

This time two years ago there was little snow left on the mountain.  In 2010 it was virtually all gone.  

If you project the green line to zero for thi year and it’s entirely reasonable to see the snow last at Trinity until July 10.

By this time the past two years the pool at Anderson was nearing full.  This year it’s a late and fast fill.

The flows from Anderson Ranch are now 2,000 cfs and the inflow is 3,000 cfs or more counting all the tributaries.  The Featherville gage looks to be in the 2,600 range.

Lots of Snow at Trinity Mountain

The snowpack at the Trinity Mountain site is well above levels seen the past two years. It is running about 125 percent of average for this site, both for total precipitation since October 1, 2010 as well as snow water equivalent snowpack.

The total snow on the mountain increased in March and April to the point where we had to adjust our graph.

We will look into previous high flow years to see how the flows expected in May and June.  

SOUTH FORK BOISE RIVER —Pierce Creek Reconnection

I am pleased to announce that the Ted Trueblood Chapter was recently awarded a $107,000 grant from the Southwest Idaho Resource Advisory Committee to restore fish passage between Pierce Creek and the South Fork Boise River.  We will remove a culvert that has been a fish blocker.  Our final push to make this project happen is the May 14 Fly Casting Tournament. See below for more information where you can participate and help.

Chris Jones

President, Ted Trueblood Chapter

Some Background on Pierce Creek

Pierce Creek drains the southern flank of House Mountain (7700’) within the Boise National Forest, flowing 3.9 miles west to its confluence with the South Fork Boise River near the Danskin Boat ramp. Approximately 100-yards upstream of the confluence, Forest Service road #113 crosses Pierce Creek which flows under via a 48-inch diameter metal culvert. This culvert effectively prevents upstream fish migration to historic spawning habitat (1.9 stream miles).

Rainbow trout spawning habitat remains at a premium within the S.F. Boise River corridor given the nature of the river. Due to the managed river flows below Anderson Ranch Dam, recruitment of spawning gravels is extremely limited.

Pierce Creek maintains the characteristics of a cold water, freestone mountain stream with moderate gradient and ample riparian cover throughout its length. While the lower reach exhibits some nontrivial silt recruitment, the remaining sections maintain abundant spawning- sized gravels and cobbles in a relatively pristine condition. A 2008 USFS fisheries survey of S. Fork Boise River tributaries showed Pierce Creek among the highest of potential spawning streams within the South Fork drainage.

Idaho Fish and Game surveys of the stream in the 1970s indicate the tributary had a spawning run numbering in the hundreds of fish.

The Ted Trueblood chapter has a work plan in three stages. Our initial stage involves planning and consultation to design, engineer and receive permitting for the Pierce Creek culvert replacement. The second stage involves culvert removal and replacement with a bridge. The third stage entails utilizing Chapter volunteers for bank and road cut stabilization using new vegetation plantings and slope management techniques. Also expect to see education and public outreach efforts to engage and expand our membership.

We are well into the first stage with the permission from the Mountain Home Highway District and the Boise National Forest having completed the environmental assessment. The road is in the Boise National Forest but the Mountain Home Highway District holds an easement on the road.

The project will also be the catalyst to address some erosion issues in a dry wash next to the old Danskin boat ramp. A new basin will trap sediment and keep it out of the South Fork Boise.

Snow Piles Up on Trinity

The last post reported on the water stacking up in Anderson Ranch Reservoir.  Here’s a snapshot of the snow in the headwaters, at least at one station.  Trinity Mountain seems one of the more important sources of water for the South Fork Boise River.  Here’s a comparison chart of the 2009 snow compared with 2010, and then another chart that overlays the 2011 snow depth accumulated so far.

There are lots of other factors to consider.  Water content of the snow for one.  How fast this snow is going to melt is another.

The combination of a reservoir pool with more water than last year and well above average, plus a good amount of snow in the high county points to some high flows this spring and early summer in the South Fork Boise below Anderson Ranch.

WATER PILES UP

There is more water behind Anderson Ranch Dam this year than at this time a year ago.

There is much more water behind Anderson Ranch Dam than in an average year.  Usually in the winter the water should be draining from the reservoir but this year and last year the water coming into the pool has been enough to match the 300 cfs outflow.  Check out the two graphs.  The only difference is the change in the blue line.

Next, we’ll look at snow accumulation and post something soon.  The combination of snow accumulation and lots of water already stored behind Anderson Dam could mean a large run-off this spring.  A cleansing flow for the river bed.  Also higher flows which makes wading and floating a more complicated situation.

South Fork of the Boise during the salmon fly hatch.

Thinking back to summer, big flows, big fish on dry flies.