Monday, June 4, 2012

Salmon At Salmon

Click to see larger version--The top is real obvious now.
(Final Update & Revision--9 pm June 6)  Well, everything's peaked: Valley Creek, Yankee Fork, Salmon @ Yankee Fork and Salmon @ Salmon.  The 5550 cfs (8.19 feet) held as the peak on the river up at Yankee Fork and the 9660 held down at Salmon City.  It sure was a wild ride since the May 3031 low flow ebb of this cycle.  But it's over.  Barring another major spring (or early summer) storm, this should be the past peak of the runoff season.  The river and its major tributaries should now all obey the Law of Gravity and move lower as the water volume runoff reduces throughout the watershed.  The only questions at this point and "How Low?" and "How fast to fall?"  We're going to hold off on predictions until mid-June.  By that time, we ought to be able to lay out some pretty reliable parameters for how the summer flow will evolve.  This has been a really fun flow event to watch.  We never would have dreamed there was enough snow out of the Memorial Day storm to rally the river this high.  We weren't alone.  Even the River Forecast experts called early peaks as the rise began.  We were all wrong.  The river flows to its own heart beat and it's wonderful to watch it work. Our 3 pm revision is below followed by the 7 am update this morning.
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(Updated & Revised @ 3 pm June 6.)  As of mid-afternoon Wednesday, it appears the Salmon @ Yankee Fork has peaked.  It's fallen from 8.19 to 7.73 and lost ten percent of its flow.  What with the current cool weather, that's a pretty good sign it's peaked.  Yankee Fork has clearly peaked, dropping from 2000 to 1200 cfs.  Valley Creek has probably peaked as well.  The Salmon at Salmon is only a couple hundred cfs off its peak so, once again, we can't make a definitive call just yet.  We're guessing it's peaked but need more data to be sure. We began this post on June 4 and have revised and updated it about 10 times since then.  The narrative below the dashed line was our last revision at 7 am this morning.
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So, what's been happening with the The Salmon River's flow at Salmon, Idaho?  The Salmon @ Salmon has sure been rockin' and rollin' the past few days as the flow has gone up, up and away.  As of 5:30 am this morning, river reached reached 9,660 (6.26 feet).  As we write this, the flow has only backed off two one-hundreths of a foot to 9660 cfs.  Can it go higher? It's entirely possible the river has one final bump up in flow.  However, it's virtually certain that June 6th will be logged as the peak of the flow cycle.

Cold weather arrived yesterday throughout The Upper Salmon River watershed. Stanley spent most of its daylight hours in the 30's.  The overnight low was 28 and it's now only 30 degrees there. Both Challis and Salmon are shivering around 40 degrees this morning.  Meanwhile the weather forecast calls for even colder temperatures tonight.  That type of weather shift almost always knocks the props out from under a high flow event.

It already appears The Salmon at Yankee Fork peaked at 5550 cfs (8.19 feet) at 10:30 pm Tuesday.  Yankee Fork has clearly peaked and is heading lower.  Valley Creek is still playing tag with the 1000 cfs level but it's definitely very susceptible to the cold weather.  We expect it to start dropping soon.  Meanwhile what few smaller tributaries are monitored by the USGS also show downward trends.

If the Salmon at Salmon rises about 9660 it will be a short-lived surge reflecting residual water from yesterday's upper watershed flow.  Chances are the hydrograph will show a clear top by early evening today.

The culprit for this welcome, protracted flow surge was the Memorial Day storm's snow deposit.  Apparently, the US NRCS SNOTEL sites didn't really reflect the actual extent and depth of the storm's snow deposit.  Galena Summit, for example, showed its snow was completely gone on June 1st.   Bear in mind, the Salmon @ Salmon reached 4000 not even a week ago on May 31 so this morning's level at Salmon is a 240% increase in flow as defined from the low point of the last cycle.

As of this narrative revision, The USGS hydrograph of the Salmon at Salmon shows no indication whatsoever that the water volume there might be attempting to stabilize. However, the colder weather and up river gages can't be ignored.

Whatever the peak here turns out to be and whenever it takes place, there's a pretty good chance that this will be the final peak of spring runoff. (Disclaimer: additional heavy wet snow storms will void that prediction.)  There's also pretty good chance the Salmon at Salmon will begin a slow recession from this peak forward.

In any event, the net result of the Memorial Day storm and this runoff event has been to create a major shift in expectations for the spring-summer runoff pattern.  Prior to the Memorial Day event, things weren't looking real good for early season river flow of the Salmon at Salmon.  The river had dropped down to 4,000 cfs much earlier than normal.  Without the additional bump in flow from the storm, it was looking like the early summer levels were going to be much lower much earlier than usual this year. Now the timing of the seasonal decline is pretty much back to normal.
Hydrograph current as of 7 am June 6th

Naturally, we have a hydrograph to discuss.  The graph above shows the Salmon at Salmon flow from March 1-June 6.  The high peak was the result of rain on the snow pack in late April.  That peak flow was 12,600 cfs at 6 pm on April 27.  The two subsequent May peaks were the result of unseasonably warm weather.  The first peak was 8250 cfs at 11:30 pm May 17 and the second was 7730 at both 8 am and 4 pm on May 23rd.  Obviously, the cycle's peak last night totally obliterated both of the May peaks.

After the river hit 7730 on May 23rd, it went straight south to 4,000 in a mere 8 days.  We prepared several years of hydrographs to compare and contrast recent annual recession patterns.  You can click here to see them as well as a little commentary, too. The impact of the Memorial Day runoff is going to make a major change in the assumptions discussed with those graphs.

Once the peak is in place for this rise, the flow should once again begin its normal seasonal decline.  This particular flow increase served to put the river's flow pattern pretty much back to normal and may indeed help forestall super low flows coming much earlier in the season.  It's definitely a better scenario than the one we had just a few days ago. As always, it certainly is interesting to see how River Reality actually unfolds.

Many Cheers, jp

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