Sunday, May 20, 2012

Was 2009 a similar year?

The USGS has a huge amount of data for stream gaging sites.  We like to look at the annual date and volume of each year's peak flow.  The Salmon at Yankee Fork has two types of annual peak personalities.  The first is a classic single peak with a steady recession until late summer.  The second profile involves an early peak, a sharp drop and then a secondary peak that's not quite high enough to take out the volume of the first peak.

Our year of 2012 here is a peak of the first type.  It's going to be a single peak at modest volume following by a steady drop in daily flows until the salmon run is finished in coincidence with the autumnal equinox.  We check many of the seemingly analogous early peaks for the Salmon.  Most all the recent ones were followed by secondary peaks, usually a month later.

The year that might best fit our study of the 2012 stream flow is 2009, even though that particular peak took place on June 6.  The daily mean flows are shown here with a red "X" to the left of June 6 and a red "Y" for the flow 30 days later.
Note that the stream flow dropped 40% within about two weeks of the peak.  Afterwards, the flow began dropping roughly 50 cfs each and every day during early July.  We think that's what's going to happen this year.  We fully expect the Salmon flow at Yankee Fork to be about 3,000 cfs by May 31 and then to begin losing roughly 50 cfs each following day. If the river drops lower than 3,000 cfs by the end of May, we're going to be looking at mid-August flows below 500 cfs.  Here are our flow predictions for the Salmon at Yankee Fork this season:

May 31 = 3,000
June 15 = 2,250
July 1   =  1,750
July 15 =  1,500
Aug. 1 =   1,000
Aug. 15 =  600
Sept. 1  =  450

These predictions are for normal conditions.  A hotter and dryer than normal summer will reduce the above volumes.  Conversely, an unusual monsoon pattern could increase these flows.

The general recreational rafting and floating season for the Upper Salmon runs from roughly late June through late August, peaking in early July.  Flows appear, at this time, to be more than adequate for commercial and private boating activities to take place as usual.  However, late season float trips could be hampered by both unusually low flows and heavy smoke from a robust fire season.

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