More on Water Levels

Kansas maintains an observation well network that it measures each year to track changes in the water level depths across the state in its major aquifers.  The annual measurements vary, usually between 1,200 and 1,500 wells, based on how many wells can be accessed each year, but a solid attempt is made to return to the same wells each year.  The 2012 measurements were taken from 1,327 wells, for example.

The statewide average change in water levels between January, 2011 and January, 2012 was a 2.28' decline.  The overall range was from a 13.63' rise to a 23.68' decline.  Keep in mind that 2011 was a very dry year for the southern half of Kansas.

An interesting look at the January, 2012 data (January, 2011 to January, 2012 change) is by GMD.  The GMDs in Kansas do not cover the entire state, but do cover 85% of the groundwater producing areas.

  GMD 1 (West Central):  1.58' decline (range: 4.85' rise to 15.57' decline)
  GMD 2 (South Central):  3.12' decline (range:  2.91' rise to 11.67' decline)
  GMD 3 (Southwest):  4.05' decline (range:  13.63' rise to 23.68' decline)
  GMD 4 (Northwest):  .57' decline (range:  4.6' rise to 5.48' decline)
  GMD 5 (South Central):  2.96' decline (range:  5.28' rise to 9.72' decline)

While I'd like GMD 4 management programs to take full credit for the state's lowest (by far) average decline rate in 2011, the truth is that our area had way more rainfall than the other areas.  We were still below average (a bit on the dry side) but not near as dry as the other GMDs.

Another way to look at the relative impacts might be to focus on the lone Index wells for each of the western GMDs.  From the 2011 calendar year pumpage, our GMD 4 (Thomas County) Index well dropped 6.69' - from a recovered level of 212.40' on March 17, 2011 to a low of 219.09' on September 4, 2011.

As of August 5, 2012, this same well has dropped 6.95' - from a recovered level of 213.70' on April 27, 2012 to a new low of 220.65' on August 5.  And the irrigation season might have another 3 weeks to go, so we expect additional declines to come.

All this to say that the GMD 4 average annual decline rate of somewhere around .5' per year may get blown out of the water this drought year of 2012.

And Then There are the Earth Tides...

I blogged earlier about the difficulties of measuring groundwater levels here in Northwest Kansas (here) and (here).  What with the effect barometric pressure has on the water levels, and the time-critical date-of-measurement relative to recovery stage, it'd seem a careful hydrologist wouldn't have a chance at an accurate measurement!  But I have not yet discussed Earth Tides - yet another influence on water levels.

Earth tides are caused by the same mechanism that causes ocean tides - the gravitation forces of the sun and the moon on the rotating earth.  The elasticity of the earth allows it to deform as it rotates through the gravitational pulls of the sun and the moon causing pressure differentials that affect groundwater levels.  The data shown to the right are from a deep well in Oklahoma and show the 6-hour and 12-hour earth tidal effects on the groundwater just over a half mile below the earth's surface.  While the ocean tides are affected normally by about 3 feet, the earth deformation is typically only about 8 inches.

The good news is that the earth tides are pretty difficult to pick up in shallow wells because the effect is really quite small and all the other influences (temperature changes, barometric pressure, pumping wells, local recharge events, etc.) are considerably larger and almost always drown them out. They are also very variable as the tilt of the earth and the constantly changing positions of the sun and moon cause different gravitational forces on the earth throughout the year.  Of course, the moon, being considerably closer, has more gravitational affect on the earth than does the sun.  But when both these bodies line up (or are fully opposite each other) their gravitational forces become cumulative and we experience stronger tides.

Science has in several places connected the tidal forces on earth to earthquakes, but the details are not fully understood.  The earthquakes would have happened anyway because of the shifting plates, but the daily waxing and waning tidal forces push and pull just a bit harder it seems. There is a definite correlation to Spring tides and increased earthquake activity in several places on earth.

Bottom line - I thought you might be interested in earth tides and we should all know they exist, but I'm not going to get too exited about trying to coax out their affect on my water level measurements!