Pumping - Precipitation - Conservation
and Stream Flow

What causes the flow in the stream to fluctuate?  Why is there less stream flow now as compared to 50 or 100 years ago?  Does the stream naturally go dry during dry periods?

There are a lot of things to consider when trying to answer the questions.  

1. Conservation Practices
2. Increased Vegetation
3. Aquifer Pumping 

1. Conservation Practices - Terraces, retention ponds, and minimum till farming practices have done a great deal to eliminate run off from fields.  These conservation practices have been encouraged and required by the government.   The government believes they are important to reduce erosion and to help prevent floods.  James Koelliker, Professor and Head of Biological and Agricultural Engineering at Kansas State University, released a graph showing the effect on stream flow of various conservation practices. As one can see from the graph, conservation practices mandated by the government have a very significant effect on stream flow.  [Definitions: "Ponds" = Retention Ponds; "Residue" = Minimum Tillage.]  Based on the studies done by Koelliker we estimate that terraces, minimum till farming, and retention ponds have reduced stream flow in the URNRD by about 60,000 acre feet each year.  Koelliker is doing another study now that he hopes will be able to put more precise numbers on the effect of conservation practices on stream flow but there is no timetable for its release.  Kansas Study says CRP results in less water in the stream and that conservation practices are responsible for 60% to 80% of the stream flow decline.   Koelliker also estimates that conservation practices are responsible for about a 50% reduction in stream flow during flood events.

2. Trees - In the 1800's, Nebraska was known as the "treeless prairie."  Even eastern Nebraska had few trees.  Central City, Nebraska, used to be called "Lone Tree."  "The original Lone Tree was a giant solitary cottonwood, which was reportedly visible for 20 miles in either direction." Central City is now a very wooded town.  Frequent prairie fires eliminated most of the trees throughout the Great Plains.  Arbor day was started in Nebraska because people wanted trees.  On the first Arbor Day in 1872, over 1 million trees were planted.  The local Natural Resource District plants thousands of trees each year because people like them and want them.

However, trees, like all plants, use water.  Cottonwood trees, which are very common along the rivers, have a large effect on the stream.  As one looks at the stream flow data, it is important to consider what the amount of vegetation along the stream was when comparing the data.  

The Colorado Tamarisk Commission, which is a coalition of universities, environmentalists, and government agencies, conducted a study for the State of Colorado.  The Governor of Colorado issued an executive order regarding controlling trees.  The commission reports the amount of water both Tamarisk and Cottonwood trees use.   This excerpt is taken from http://cwcb.state.co.us/Resource_Studies/Tamarisk_Study_2003.pdf

"From thirteen different studies conducted between 1972 and 2000 on tamarisk evapotranspiration rates, the average water use reported is approximately 5.3 feet per year (Hart 2003). More recent work performed on the Pecos River in Texas over the last three years indicates water use by tamarisk of 7.7 feet per year (Hart 2003). Recent research by the U.S. Department of Interior on the middle Rio Grande estimates evapotranspiration rates on the order of 4.3 feet per year (Interior 2003). These studies were performed using different methods of measurement, at different locations, and for different densities of infestation. Native cottonwood/willow communities have been estimated to use approximately one foot less per year than tamarisk (Weeks, 1987) while the native shallow-rooted upland plant communities of grasses, sage, etc. use only the moisture received by precipitation. Unpublished research on the Bosque del Apache National Wildlife Refuge on the middle Rio Grande River in New Mexico indicates that

Russian-olive has very similar evapotranspiration rates as tamarisk (Bawazir 2003).  [Pg 15.]

 

Tamarisk is rapidly spreading throughout Colorado and the surrounding region. Efforts to control this aggressive plant species have been unsuccessful. It is now estimated that the plant has overcome native species on 1.5 million acres throughout the region and it is has become apparent that the plant is causing serious ecological and environmental problems within the State of Colorado .

 

The tamarisk plant consumes an enormous amount of water. A single tamarisk tree can transpire up to 300 gallons of water per day. As a comparison, an average acre of native cottonwood trees uses 845,000 gallons of water per year (31 acre inches), while an acre of tamarisk uses 1.3 million gallons of water per year. An accumulation of tamarisk plants close to a watershed can effectively limit or dry up an entire water source. The disproportionate consumption of water by a non-native invasive species is cause for serious concern for Colorado as it continues to endure one of the worst droughts in state history. [page 27, executive order by Governor of Colorado]"

Colorado recognizes the volume of water that trees along the streams consume.  They have decided to remove many of these trees, as they are drying up the rivers and streams.  The Republican River in Nebraska has approximately 121,000 acres of cottonwood trees.  Using the Colorado data of 31 inches of water per acre of trees, water consumption by trees along the Republican River is 314,000 acre feet of water.   

The URNRD along has planted over 500,000 trees in the last 25 years. While many of these trees are far from the stream, they do capture precipitation and reduce the amount of water that can percolate into the aquifer or run off into the stream.

2. Aquifer Pumping - According to the DNR, pumping water from the aquifer will have a delayed effect on the stream.  Water pumped this year will not effect stream flow this year but some time in the future.  The closer the well is to the stream, the less time it will be before the effect is seen.  The following graphs show what the DNR reports is the effect on the streams by ground water pumping in the Upper Republican NRD.  The first graph shows what the stream flow would be if every well within 2.5 miles of the streams were turned off.  It takes about five years before the full benefit of turning off wells is realized at the streams.  To get the acre feet results shown here, 88,000 acres pumping 90,000 acre feet must be turned off.  For the Upper Republican NRD, 23% of the water pumped from a quick response well would have been in the stream if not pumped.  The other 77% would never have entered the stream.  Right or wrong, this is what the scientists hired by the DNR say would happen.  This idea has been accepted as reality by Kansas, Nebraska and Colorado water policy officials.  

The effect on the stream by wells far from the river is much slower.  The DNR has never released details for wells far from the stream.  It has only released total averages.  The averages include wells from 2.5 miles to 40 miles from the stream.  Every hydrologist will agree that wells 30 miles away from the stream will not affect the stream flow nearly as quickly as wells close to the stream. 

The DNR shows that if you shut off every well in the URNRD, the stream flow would increase by the percentages shown.  These numbers are a percentage of the total amount that would have been pumped, but was not.

So, if 300,000 acre feet of upland water was not pumped because every well was turned off and kept off, then the stream flow would increase years later by:

Please look at the following two charts and decide which is more closely related to stream flow.  Remember that, according to the DNR, pumping has a multi-year delayed effect on the stream. 

The graphs begin in 1951 because this is when the stream gauge was put in place at the point in the river for where we have data.  Also note that 1951 was one of the wetter years at about 26 inches of precipitation while normal is 19.

Koelliker estimates that conservation practices are responsible for about a 50% reduction in stream flow during flood events.  His report would account for the missing spikes in stream flow during wet years. 

Note:

• Large amounts of water were not withdrawn from the aquifer until the 1970's. 
• There were wide swings in stream flow before irrigation began.  
• The stream no longer peaks as high as it did.
• Conservation practices became common in the 1980s.  
• Tree growth along the rivers increases each year.

Conclusion - Many of the people involved in the water issue are "talking past each other."  Many come to the discussion with opinions formed before looking at the data and the facts.  Data that does not support preconceived ideas is usually ignored, denigrated, or disputed. One thing is clear.  There is a serious shortage of data on key questions.  Recent changes in water policy have placed all of the responsibility of stream flow declines on the shoulders of ground water irrigators.  This is obviously unfair.  Conservation practices that most everyone supports are also responsible.  Uncontrolled tree growth along every stream also makes a very large impact on the stream flow.  

Kansas Study says CRP results in less water in the stream and that conservation practices are responsible for 60% to 80% of the stream flow decline.

Based on a comment from someone identifying themselves as jtr, I have modified the above graph to include the words, "since 1930".  For a more detailed explanation of what this means please read, Causes of Stream Flow Increases and Declines.

Any solution will need to recognize each of the factors affecting stream flow and address them.  Placing the burden on one factor while ignoring other factors will not result in a solution that creates a sustainable system.