Monday, October 1, 2012

Water Year in Review

Most folks live by what's called "the calendar year."  It begins with a big celebration on January 1st.  Hydrologists and water managers live by what's called "the water year."  Today is their January 1st.  The water year begins again each October 1st.

The water year is designated by the calendar year in which it ends.  Therefore, yesterday was the end of Water Year 2012. Today is the beginning of Water Year 2013. Use of water year as a standard follows the US national water supply data publishing system that was started in 1913. This time interval is often used by hydrologists because hydrological systems in the northern hemisphere are typically at their lowest levels near October 1. The increased temperatures and generally drier weather patterns of summer give way to cooler temperatures, which decreases evaporation rates. Rain and snow replenish surface water supplies.

The graphics below will provide a starting perspective about the most this and past water years. (Comments below each graphic.)

 The graph above tells a tale.  You can see the water year began last year almost exactly where it is this year.  Obviously, some precipitation took place and double the flow.  After the affects of this mini-surge subsided, the river continued its slow decline to the winter low flow levels.

Typically, The Salmon River at Yankee Fork will begin to wake up in March.  This year was no exception.  The first high spike was boosted by some rainfall on the snowpack and created the peak flow for this year year in late April. A secondary peak is normal under such conditions.  This year was somewhat of an anomaly in that there were two nearly identical secondary peaks with the last taking place in early June.

After the bulk of the snowpack has melted, the river will typically begin an orderly decline into the salmon spawning season.  The salmon are dialed in to knowing when the water levels will be most favorable for making their redds.  You can note a very slight increase in the flow level over the last couple of weeks.

Although the long-term daily mean data for the period of record (1922-2011), it may be a reasonable guess that Water Year 2012 finished at a slightly higher level than the long-term norm.  We hope the USGS can soon clarify that for us.  Now then, let's take a look at the two tables below.

 For whatever reason, there is no USGS data available from 1991-2001.  That's an abnormally large gap in long-term data!  However, we do have about 20 years worth of data here for the "daily mean flow in cfs" for the Salmon at Yankee Fork.  In simple terms, these number attempt to quantify a theoretical number that would take the whole water year flow and average it out as a daily flow.  It's an easy way to see if one water  year was more or less productive than any other given water year.

We are hoping we obtain the "total discharge in acre-feet" for the water years of record.  That's yet another of many years to compare and contrast water years.  Obviously, the provisional data for Water Year 2012 hasn't been posted yet.

You can see from the above table that Water Year 2011 had the highest daily mean for the past ten years.  It will be very interesting to see if Water Year 2012 exceeded the 2011 figure. It's highly unlikely because last year was such a "big water year." However, we heard lots of Old Timers grousing all summer about how "the high water" was affecting fishing, so it will be interesting to see the difference between 2011-2012

Now this is definitely an interesting water year graph.  As with the Yankee Fork, the USGS gauge at Salmon, Idaho started the water year off with a nice dose of precipitation and nearly doubled in flow.  It tapened down into December and appears to have bumped up once again going into the beginning of the calendar year.  As usual, the flow fell back to base of about 1,000 cfs in the depths of frozen winter.  The melt awakened a little early but did not begin in earnest until the usual March time frame.  The Salmon's spikes at Salmon mirrored those of the Yankee Fork, as did the orderly decine into salmon spawning season.  The interesting aspect of this water year graph shows the river flow making what appears to be a new annual low just last month.  (Without the missing data, we can't be 100% certain.)  Secondly, the flow actually rallied from the early September lows despite the lack of precipitation in the watershed.

Our guess from this graph is that irrigators took more then normal water during the hot late summer phase and then reduced their demand as the recent temperatures have cooled off.  In any event, the river flow at Salmon finished the water year about where it always does, roughly around 1,000 cfs.

Note that the USGS does not provide water year graphs for gauge height.

The data from the Salmon gauge is more complete that the Yankee Fork gauge so we have daily mean values for each water year dating back to 1913.  Note that last water year's daily mean was the highest since 1997!  We doubt that this most recent water year's value will come close to the 2011 figure as the cfs values ran below median all summer long, contrary to the Yankee Fork data site.

Thanks for reading and Happy New Water Year!  jp

The graphic below was received from the USGS on October 9th. You can click on the graphic itself to see a larger, more readable version.  We will post further analysis of the data here soon.


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