The Winter Solstice Arrives!

Today marks the beginning of Winter — at least in the Northern Hemisphere.  (Happy Summer to our friends south of the equator!)  This is the day with the smallest amount of sunlight hours, and the sun is the lowest in the sky.  Our ancestors were amateur astronomers, gazing at the sky as we do today, and this day — like its counterpart, the Summer Solstice — became a day of great significance in their lives as Winter approached.

It is also a day of great significance to Water System Operators.  As we enter the coolest and (at least here in the southwest USA) wettest months of the year, we need to recognize the impact that the Winter climate will have on our operations.  Two key things come to mind.

First, we look to our storage situation.  Here is today’s report from the California Department of Water Resources:

http://cdec.water.ca.gov/cdecapp/resapp/getResGraphsMain.action

The report is good: we have a lot of water in storage, thanks to last year’s excellent precipitation.  But we do have to recognize that many of our reservoirs serve not only as water supply facilities, but also as flood control tools.  And a full reservoir cannot provide any flood control!  So, if your reservoir needs to provide this service too, you should be looking to drop reservoir levels at this time.

Next, in our distribution systems, our customer usage will be way down.  If we look at the Flow Rate Equation (see MOST Course WM-4), we can see what that means: increased Time — or “Water Age” — in our systems.  And old age is a bad thing for water quality.  Increasing disinfection by-product levels, nitrification, and biological growth are all likely as water age increases.  As system Operators, we should be looking to address this by reducing storage within our treated water reservoirs, if possible, and to unidirectional flushing — especially in areas of low water consumption.

Incidentally, we plan to finish up MOST Course WD-2 on Reservoirs in the near future, so be looking for it soon.

So let’s use the cosmic event of the Winter Solstice as a reminder to re-evaluate our system operations and prepare for the differing operational circumstances that we will face in the next few months.

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