Quantities are in acre feet

Chase County Nebraska Water Balance

Using a variety of sources, WaterClaim has compiled a Chase County Water Budget.  The Nebraska Department of Natural Resources (DNR) has participated in the creation of a computer simulation that would permit the same type of summary for each county in the Platte and Republican River Basins.      

Between the 1800’s and now, water use by grass has decreased by about 447,000 acre feet a year, while crop water use has increased by about 454,000 AF.  This means crops are using about 7,000 AF more water than grass did.

There is more water entering the aquifer now than there used to be; but more water is pulled out of the aquifer, too.  This is a net loss to the aquifer of about 100,000 acre feet a year.

There is more water on the surface of Chase County than there was in the 1800’s.  The precipitation has remained the same but the supply is increased by about 200,000 AF as water is moved from the aquifer to the surface.

Even though there is more water on the surface, there is less water in the stream.  Stream flow has declined by about 46,000 acre feet and tree use has increased by about 20,000 acre feet.  The remaining reduction in stream flow is due to a combination of conservation and reduced base flow.

Conservation, terraces, grassed waterways, retention ponds, and minimum tillage have kept more water on the land where the precipitation falls.  This has reduced run off and made more water available to the vegetation.  Conservation reduces irrigation needs, increases evaporation, increases aquifer recharge, increases the amount of water available to vegetation, and reduces run off into the stream (reduces stream flow). 

For Chase County to comply with its portion of the requirements of the Settlement Agreement with Kansas, it needs to cause about 6,500 more acre feet of water each year to be in the stream than there is now.  This is the equivalent of pumping the water that is used on approximately 50 center pivots and putting it directly at a stream gage.  The closest gage is near Culbertson.  That would require many miles of pipe or Chase County taxes to be spent outside of the District.  Also note that if the water is sourced from within the Basin, additional water will be required, as Kansas owns a portion of what is pumped.  Pumping from within the Basin to augment the stream will borrow against a future generation so that we can continue to pump.

Or, we could turn off all irrigation wells close to the stream for several years.  There are about 50,000 Quick Response (QR) acres in Chase County (25% of the irrigated land in the county).  According to the Model, turning off all wells close to the stream would cause the stream to have another 6,500 acre feet of water, if the wells were left off for at least five years.  However, the Model does not take into consideration the presence of trees or conservation and, hence, is probably very wrong about that assumption.  Also, we are not recommending this approach; we are just pointing out what the Model says and, hence, what would be required for Chase County if this option were chosen.

The same result could be achieved by reducing water usage by trees by about 45%.  However, for the tree reduction to be counted, the savings would have to occur by getting the water past a stream gage.  Therefore, an equivalent number of trees would need to be removed just above some stream gage. There are about 30 miles of heavily-treed stream in Chase County.  We are not suggesting this be done; we are only indicating what would be required in order to comply via this solution.

The most cost effective way to comply with the Compact requirements is to augment the stream.  This can be done in three different ways. 

·        The water stored in the reservoirs for surface irrigation can be sent past a stream gage rather than used on Nebraska crops. 

·        Water can be pumped out of the aquifer and placed in the stream.  This requires pipelines from areas where the effect on the stream is delayed by many years but yet close enough to a stream gage to make this affordable.  Several such locations exist, but this option requires the consent of Kansas before it can be implemented.

·        Water can be brought into the Basin from the Platte River Basin.  This is the least expensive option; however, there are many (both within the Basin and outside the Basin) who are opposed to this option. Those opposed to this option generally prefer a significant reduction in the amount of groundwater irrigation, regardless of the effect on the economy.

All irrigation in Chase County (385,000 AF each year) could be eliminated for five years; according to the official computer simulation, the stream flow would increase by about 6,500 AF -- from 14,000 AF a year to 20,500 AF a year.   Compliance via the elimination of irrigation is less than 2% efficient.  Reducing allocations may sound good, but it accomplishes even less.

Water Balance for Chase County Nebraska

Explanation by line:

Statistics

Total Acres – Square miles multiplied by 640.

Irrigated Acres – Source URNRD.

Dry Crop Acres – NASS reports total acres in crop land.  We compare their number to the URNRD irrigated acres and use the result as the dry acres.

Range Acres – NASS reports total range acres.

Other – Total acres minus total NASS crop and range acres.

QR – Quick Response areas.  An arbitrary line drawn for ease of administration.  Generally about 2.5 miles on each side of the stream and tributaries.

Where the water comes from

Precipitation in AF at 19 inches – Average precipitation for the Champion gage has been 19 inches a year.  Total acres multiplied by 19 inches divided by 12 to yield acre feet.

Pumped from the Aquifer in 2004 – This number varies considerably from year to year; but we use the 2004 usage of 12.41 inches per irrigated acre as the average.

Total underground inflow and outflow – The reason this number is 0 is we have no knowledge of what this number might be.  The RRCA model computes this number, but we do not have access to it.  For our purposes, we assume the inflow balances with the outflow.   It is placed here to show we recognize it could be a factor.

Where the water goes

Aquifer Recharge – The 99,580 AF is the number used by the RRCA model.  The Model assumes a 20% recharge on irrigated acres.  If the land is grass, then this 20% recharge bonus would not be present. 

Enders evaporation – The 2004 evaporation, according to the RRCA model, was 1,500 AF.  In the 1800s, Enders Reservoir did not exist.

All other evaporation – This number is an educated guess.  It represents water that evaporates off of streets, ponds, and lakes.   The assumption is that, in the 1800’s, there were very few areas that were not covered with grass.  The only ponds that existed were buffalo wallows.  Now, there are many streets, retention ponds, terraces, etc.  Remember that the surface area of Enders Reservoir evaporates 1,500 AF.

Run Off – This is a measure of the Frenchman Creek stream gage at Palisade.  This measures all drainage from Chase County.  It includes a small part of Hayes County.  The 14,622 AF is the current stream flow.  The 95,000 AF is the flow that the RRCA said would have been present prior to the 1940’s.  See dry crops.

Transpiration

Irrigated Crops – Crops such as corn, irrigated wheat, and dry beans will use the full amount of water available to them, up to the evapotranspiration rate for that plant.  At Champion, corn uses 25.8 inches, wheat and sugar beets use 22.0 inches, sunflowers use 26.4 inches, soybeans use 18.5 inches and dry beans use 13.5.  Alfalfa and grass will use over 50 inches each, if it is available.  We use an average of 24 inches per irrigated acre.

Dry Crops – We assume that 45% of the dry crop acres are fallowed and that 80% of the precipitation is transpirated by the plant.  The other 20% is assumed to either evaporate, seep into the aquifer, or run to the stream.

Grass – We know the approximate aquifer recharge rate, the run off, and the other water uses in the 1800’s. This allows us to estimate, with a high degree of accuracy, the amount of precipitation captured by grass.  The buffalo grass has a root depth of about 5 feet.  For water to penetrate beyond this depth and enter the aquifer, it must saturate 5 feet of rooted soil.  Grass can access more water than can corn and wheat with their shallower root depth.  Aquifer recharge is greater on non-grassed areas.  Trees were nearly non-existent in the 1800’s, and we know that grass uses about 86% of the average precipitation.  Multiply the current number of range acres by 86%, and we have current grass water usage.

Trees – See “Grass” paragraph above.  As few trees existed in the 1800’s, we know they took very little water.  By accounting for all other uses of water, we know the balance is probably taken by trees or conservation.  These numbers are based on Imperial, Enders, and Culbertson stream gage estimates.  10,000 AF was assigned to Colorado in the 1800’s.  The maximum average stream flow in the 1800’s was 60,000 AF.  Today, it flows about 14,000 AF.  This means stream flow has been reduced by 56,000 AF.  According to the RRCA Model, the 2004 depletion to the stream caused by Chase County groundwater pumping was 6,916 AF.  This leaves about 49,000 AF feet of stream flow depletion unaccounted for.  We assign half of this unaccounted portion to trees and the other half to conservation, which has caused reduced run off.

Conservation – We back into this number by assigning to it everything that we cannot account for in other ways.  Conservation consists of terraces, grassed waterways, retention ponds, and minimum tillage practices.  Conservation has kept more water on the land where the precipitation falls.  This has reduced run off to the stream and made more water available to the vegetation on the land.  Most of the conservation activities are on heavily sloped land.  While there were no conservation measures in the 1800’s, almost all land was covered with buffalo grass that slowed the run off to the stream, unless the land was highly erodable due to slope or soil type.  Most of the water usage assigned to today’s conservation occurs on non-irrigated land and range land.

Based on the information we have from the Computer simulation agreed to by the US Supreme Court and the three States in the Compact, we know it is impossible for Chase County to comply with its share of the obligation by reducing usage or even completely eliminating irrigation in the county and still maintain our economy.  All wells would have to be shut off for at least five years to cause the stream to increase its flow by the needed 6,500 acre feet.  In other words, you can shut off irrigation to 192,000 acres for 5 years and you would then get 6,500 acres’ worth of water into the stream.  That is what the official documents provided by the DNR say.    If you do not find that idea to be believable, then you need to persuade a lot of hydrologists, the Attorney General of at least one State, the heads of three different State water agencies, and the highest Court in the nation to change how things are calculated.

Either the entire simulation is flawed and a lot of professional people are wrong or this area must spend tax dollars in other parts of the State in order to buy water or to remove trees.  Whether the water is purchased near a stream gage or water is imported from the Platte River, we will be spending money outside of the County and District so that we can continue to irrigate.  Irrigators are likely to pay most of the bill -- not because they cause most of the problem (they don’t) but because they cannot afford to lose access to water.

The most effective and least expensive place to spend the money is where we get a 100% credit.  The owners of the least expensive water are open to discussions about making a deal.

An official water balance sheet (similar to what is prepared here for Chase County) for each County and NRD in the Basin would be helpful and perhaps provide the policy makers the information necessary to create not just a politically acceptable solution but also one that actually solves the problem.   It might also help dispel the very common misconceptions about why there is less water in the stream, even though there is more water in the environment.

More graphs and charts that are easier to read can be seen on the WaterClaim web site and specifically at www.tinyurl.com/223xo6

Contact steve@waterclaim.org if you would like an easy to print version of this.