Friday, May 25, 2012

River's dropping

What goes up must come down.  After all, the Law of Gravity applies to all watersheds and their rivulets and rivers.  So it is that The Salmon River had now entered its seasonal decline.  The river began to recede only a couple of days ago after one last surge of snow melt generated by near-record high temperatures in the Sawtooth headwaters area.

Currently, the river's dropping a seemingly insignificant two one-hundredths of a foot each hour.  While that sounds tiny, it really adds up fast.  That's nearly a half a foot a day and could equate to as much as 400-600 lower cfs each day.  You can click on the small graphic at left to see the full size version.  This is what the current decline looks like when graphed by the USGS Yankee Fork gauge.

Typically, any free flowing river located near a big snowpack will experience a sharp fall off in depth and flow after the snow is gone.  Don't count on this level of recession to continue very long.  The river's snow melt flow peaked on a pair of days: May 17 and May 23.  The May 17th peak was slightly higher than the 23rd but both were basically 5,000 cfs.  Today the river is already back to 3830 and heading lower by the hour.

The median flow for this time of year is about 3000 cfs.  As the river begins to approach this level, one would expect a slight change in the rate of recession.  We are optimistic that the river will be much closer to 2,000 cfs by mid-June.  All phases of The Salmon River's runoff cycle has been happening earlier this year than normal.  If that continues to be the case, expect very low flows to be in place by mid-summer.

There's always a potential wild card.  The NWS is calling for 6-12 inches of snow in the Central Mountains during the next couple of days to be following by the typical warm spell afterwards.  If the snow is wet and on the high side of their prognostication, then there yet might be another mini-surge late next week.  Chances are that won't happen but it's always a remote possibility.  Right now it's at or below freezing from Stanley down toward Challis and the main storm track looks to be south of The Salmon River's upper watershed as shown in the radar screen shot below.

Bottom Line: What goes up must come down and that's The Salmon River Story today.

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