Lag Effect

The information provided to the public and the NRD cannot be correct

 According to The Nebraska Department of Natural Resources (NDNR), all water pumped from the aquifer in the area of the Republican River Basin would have flowed naturally to the surface and into the river.  But, because humans pump the water from the ground, much of this water evaporates or is consumed, and now will never flow into the stream.

Because it takes water many years to move underground, the effect on the stream may not be seen for many years.  The NDNR has estimated the amount of time it takes for water to move underground for each square mile in the basin.  Some of the water that is in each square mile close to the stream would have flowed naturally to the surface and into the stream within three years.  For wells that are 20 miles from the stream, this may take 10,000 years.  The NDNR has an estimate for each square mile.

For those wells within 2.5 miles of the stream, the NDNR reports that it takes an average of 3 years for the water to move into the stream.  For example, if someone pumps 100 gallons of water out of the ground, then in year one, the Model says that 33% of that water would have naturally flowed into the stream but now will not.  We call this number the Depletion Factor.  In year two, another 100 gallons was pumped, 33% from year one pumping will fail to arrive at the stream plus 33% of this year’s pumping.  In year three, another 100 gallons was pumped, 33% from year one pumping will fail to arrive at the stream plus 33% from year two will fail to arrive and 33% of year three pumping will fail to arrive.     

Pumped Year 1 2 3 4 5 6 7
Yes 1 33.3% 33.3% 33.3%        
Yes 2   33.3% 33.3% 33.3%      
Yes 3     33.3% 33.3% 33.3%    
Yes 4       33.3% 33.3% 33.3%  
No 5              
  - - - - - - -
  33.3% 66.6% 99.9% 99.9% 66.6% 33.3% 0.0%

  The table shows that if someone pumps the same amount each year, then by year three every gallon pumped will have a 100% impact on the stream.  Even if pumping stops, it will be another three years before the effect on the stream stops. This is the information that the NDNR is telling the public at the public information meetings.

The NDNR reports that the quick response wells have pumped an average of 341,000 acre feet of water from 1998-2002.  If one applies the NDNR’s depletion factor of 33.3% to these wells, and these wells have been pumping for the last three years, then the model should report a consumptive use of 341,000 acre feet for these quick response wells alone.  However, the Model only reports total groundwater consumptive use to be 192,348 acre feet for all quick response and upland acres.

This means one of two things.  The Depletion Factors the NDNR is reporting to the public are not even close to correct, or that NDNR is dramatically under-reporting the actual Model results and that all irrigation must be stopped now.    If the depletion factors are incorrect, then we could retire thousands of acres of quick response wells only to discover that later Model runs show no real savings.  Then, yet another round of even more drastic cuts would be necessary. So what are the correct numbers?

We do not know.  We have repeatedly asked the NRD and the NDNR for the Depletion Factor for each square mile.  We are told the number cannot be provided.  Based on the reports that they have generated, we can make guesses as to what the correct Depletion Factors are -- but they are guesses.  At this time, all we can do is prove that what information the NDNR is giving the NRDs and the public is not correct.  

See Lag Effect Technical for a more detailed discussion.