Friday, March 25, 2011

Thomas County, KS Index Well

TH Cty Index Well
The Edwards Aquifer Authority posts daily the water levels from 2 index wells they monitor, and 2 discharge rates from important springs in the district.  I enjoy these daily posts which show very short term trends that are important to the region.  These are posted on Twitter every morning for the previous day.  You can follow them, too, at:  Edwards Aquifer Authority Twitter Acct

Based on their lead, I've added a link to our index well on our web page here:
TH Cty Index Well Link  This is an interactive page that returns a graph and the raw data for any date range you want to look at.  The readings are taken every two hours, and began in June, 2008.  This page contains all 3 Kansas index wells - you'll find the Thomas County well information and data at the very bottom.

Below is the graph of water level elevations (in feet above sea level) for this well since it began operation.  (click on it to enlarge)  This index well is NOT an active irrigation well, and is located about 1/2 mile to 1 mile from all irrigation wells in the area.  It shows the classic curve of declining water levels in the Spring and Summer as irrigation is going on, and water level recovery back to the time the declines start again for the next irrigation season.  For this well, highest recovery levels are:  2975.7' in Mar 2008; 2975.1' in May 2009; 2976.2' in Apr 2010; and 2975.1' in Mar 2011.  This data shows a -.6' change (decline) from 2008 to 2009; a +1.1' (increase) from 2009 to 2010; and a -1.1' (decline) from 2010 to 2011 (the full -1.1 decline is not shown on graph , but has been measured since).  Bottom line from this data - this well has declined -.6' over the past 3 years.

The yellow dots are the actual measured water levels taken in early January each year which become the official water level measurements.  From this official data, this well changed -1.4' from 2008 to 2009; + 1.3' from 2009 to 2010; and - .75' from 2010 to 2011.  The directions are all consistent, but the sizes of the changes are different.

The regional irrigation wells, of which there are about 6, cumulatively affect the water levels at this point about 5-6 feet every year.  Of course, the pumping levels are lower yet as you get closer to the individual pumping wells.  In some cases, Mid-August pumping levels can be 50 - 70 feet lower than the static water levels of these heavily pumping irrigation wells.  You can also see that the water level impacts are much quicker than the recovery impacts.  This has to do with aquifer parameters, which affect pumping cones of depression, which influence water levels.

It is interesting that the lowest pumping levels over the past 3 years are increasing slightly, which may or may not mean good news, while the recovery levels (highest annual points) bounce around a bit.  It's important to understand that these highs represent actual physical recovery levels and not theoretical recovery levels.  We're finding that the recovery periods would continue past the start of the next irrigation season if allowed to do so, meaning the theoretical high points are being influenced by pumping.  The question is, to what degree?  Do we need to consider full recovery levels from year to year in order to more definitively describe what the water table is doing?  We're working a bit on projecting full recovery levels, but it's a lot of assumptions and statistics at this point in time.

What I like about this arrangement is that longer term trends can easily be looked at - as opposed to just today's data, yesterdays levels, and a comparison to the monthly average.  Oh, the hourly and daily variations are due to changing barometric pressures.  A low pressure regime will cause the water table to rise a few inches, while high pressure lowers the level a like amount.  We can see a 5-6 inch rise or decline over a days time due to pressure alone.  The real serious water level data in Kansas is further adjusted for barometric influences as well - where the regional pressures have been recorded and can be correlated.  I only wish we had a bunch more of these index wells logged.


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