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  These retirements total just over 1,000 AF of irrigation water that had been pumped annually but are no longer being withdrawn.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.

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.

 

 

 

 

 

Groundwater Monitoring

I need help with the science of groundwater monitoring. Our existing observation well network consists of 287 (or so) wells that are spacially located across the district via a 6.25 mile hexagonal grid.  Statistical work said this spacing and configuration would give us an acceptable accuracy to describe the water table attitude with the least number of wells to be measured. 

Subsequent statistical analysis confirms that the current network is in fact satisfactory enough to determine, over longer time frames, the areas of the district where water level changes are relatively worse than, or better than, average.  However, it is NOT sufficient enough to monitor the water levels in smaller areas, or for shorter  time frames - which is what we need now in the designated high priority areas.

How then is the best way to improve the accuracy of these smaller observation well networks?  Is it simply a matter of density?  The pundits tell us that all else being equal and with our variability in our aquifer bedrock, it takes approximately 4 times the well density to double our statistical accuracy.  Do we use data loggers or continue with annual tape measurements?

Would an index well (or two or three) be a better approach?  Theoretically, once the index well is data logged, corrected for barometric influences and has a recovery curve applied so that its full recovery level can be ascertained, just a few of these could more accurately reflect what is actually going on in these smaller areas from year to year - and maybe even one if we choose wisely.  But then we have the issue in the short term of comparing new, corrected and massaged data with the existing unmassaged data.  And the water users are not keen on one index well replacing the 9 obs we currently have in this specific area.

I'd be interested in hearing from the science community on any other approaches that would be available for consideration - preferably other approaches that have worked in other places.