Tuesday, March 15, 2011

GMD 4 Rain - Pumping - Water Table Relationship

I continue to be struck by the simplicity of the water use patterns inside our groundwater management district.  The graph included (click on it to enlarge) shows 3 graphed data sets from roughly 1980 through 2002 - average in-season rainfall; reported groundwater pumped; and water level change.  (We used only the data from the late 1980s forward for reported water use - when our reporting process was enhanced significantly.)

When the rains come, the pumpage drops and the water table change is mitigated.  And of course, the opposite is true as well.  A really good example of inversely related data sets.  Now, if we could only get it to rain more...

One of these days I'm going to update this graph because it's so instructional.  You should note also the three trend lines included on the graph.  While the in-season rainfall and the water level change trend lines are relatively flat, the reported pumped water trend line is decidedly downsloping. 

Why, you ask, should the water level change line NOT be upward sloping if less water is getting pumped?  It's because consumptive use drives the water level changes.  While pumped water is actually declining due largely to irrigation efficiency improvements, the consumptive use of the reduced water pumped has held more or less steady.  To affect the water level change trend line, we need to reduce consumptive water use - or, make it rain more.

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