Wednesday, April 6, 2011

Predicting Full Aquifer Recovery

Trying to understand the aquifer recovery process following a pumping season for irrigation has led to some interesting things.  First, the rate of recovery is not constant, but increases as time goes by - at least in the unconfined aquifer conditions we have here.  Secondly, there are 2 distinct stages of aquifer recovery - the first being the initial 1000 hours (41 days) and the second being everything afterwards.  Thirdly, our aquifer never recovers fully before the following year's pumpage begins to drop it again.

With data loggers in a dedicated index well taking water level measurements every 2 hours since the Summer of 2007, we have data on four full recovery stages and three full pumping stages.  (See data and graphical results here)  The data has been plotted both as a semi-log recovery curve and as a Horner recovery curve - for each recovery year.  All the plots show a distinct, 2-stage recovery process.  Here is a Powerpoint update with many of the graphs and data sets.

What is so amazing is that the theoretical full recovery (as predicted by the Horner plots) will take a full year or more to happen.  This finding has implications on the true accuracy of the annual well measurements Kansas has been collecting since the mid-1940s.  This was a surprising find.

The graph included (click to enlarge) shows the projected full recovery levels for each of the three captured recovery periods as red dots.  For ease of understanding they have been assigned to the same dates as the highest physical recovery even though these recovery levels would not be achieved for another 6 months to a year. The yellow dots are the annually measured (official water levels) for this well for all four years.  Using the annual measurements, we think this well's 2010 water level was at 2974.5'.  Using the 2010 theoretical recovery level (following the 2009 pumping season) the water level would be 2978.9' - a difference of 4.4 feet.

Discerning what the water level is for any data point is simply not all that easy and straightforward.

But what is straight forward is voting on my poll.  So go ahead, do it!

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