Groundwater Levels - Thomas County Index Well

This is the graph starting on June 17, 2008 of the Thomas County Index well.  This well has a data logger installed that collects a water level measurement every hour and uplinks that measurement to the Kansas Geological Survey.  The index well is a dedicated monitoring well that sits about 1/2 mile away from any operating wells.  I've blogged about this program before, so if interested, check out the other articles - generally under the "Index Wells" or "Thomas County Index Well" labels (right side of blog page).

The point I'd like to make today is on the right side of the graph.  The last reading shown happens to be 219.78 feet below land surface on July 26, 2012, and represents the lowest level this well has ever been since monitoring began and until today as this post is being written.  I know 4 years is not much of a data set, but the fact that this level has been achieved as early as July 26 is telling.  All the previous lows were reached in late August or early September - just as irrigation was concluding for the year.  Immediately following irrigation season the water levels always begin their dramatic rise and return toward recovery - until the next irrigation season begins.  This being the pattern, it appears that this year's low is going to go significantly lower yet as irrigation season likely has at least another 3-4 weeks to go.  

Another telling fact is that 10 water rights have been retired in the general area of this index well over the past 4 years through the state's Water Transition and Assistance Program (WTAP) - within 8 or 9 miles of this index well.  These retirements total just over 1,000 AF of irrigation water that had been pumped annually but are no longer being withdrawn.  Had these 10 water rights been also competing for this region's groundwater this year, it's likely the groundwater level on July 26 would have been even lower.

You can look at this data anyway you want to, but clearly it represents some degree of a problem at some time in the future.  Should you chalk it up to the extreme drought and argue that things will look much better when normal weather returns?; or, Should you start thinking about slowing the decline rate in the hopes of extending the economic life of the groundwater supply?

That brings me back to the Local Enhanced Management Area (LEMA) process.  This index well sits very close to the middle of the TH-5 High Priority Area - one of the 6 designated enhanced management areas of GMD 4.  This area held stakeholder meetings back in late 2008 and early 2009 on addressing their declines, but haven't yet sustained enough momentum to go any further.  Perhaps this is the data that might get them more interested and involved.

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!