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Open Letter

by Wyoming Livestock Roundup

Editor’s note: This letter has been edited to meet space requirements. To view the complete letter, visit

Open Letter to Appropriators and Interested Parties in the Vicinity of the LaGrange Aquifer Subject Area,

This letter is intended to supplement the First Amended Order of the State Engineer Horse Creek Basin, issued on May 31, amending the original Horse Creek Order issued July 19, 2013.

It is important to note that since the 2013 Order was issued, southeast Wyoming has been blessed with moisture. The recent improvement in hydrology has had important impacts, including the availability of significant streamflow for surface diversions, and in some cases a marked decrease in groundwater pumpage as compared to prior years. That is all good news.

Indeed, the first three years of operation under the 2013 Order saw use of only about 48 percent of the overall groundwater allotted to groundwater irrigation uses in the subject area. Several appropriators even carried some amount of groundwater use into the next order period. This, it appears, was largely due not only to a reliable surface water supply but also to modifications made by some operators’ “plumbing” that made better use of surface water when it was available.

Still, there were some appropriators who had groundwater supplies only, and comments were received that the nominal 12 inches per year, even with some carryover, might be insufficient for their crop water needs.  Without surface water sources to augment their water supplies, some groundwater users were therefore forced to operate as though the drought of the 2000s continued.

One of the primary goals of the 2013 Order was to strike a balance that respected senior surface water rights while allowing those who depended on groundwater to continue to use that interconnected resource without fear of facing curtailment under a call for regulation every year.  In other words, it was an effort to protect all the various interests involved, while at the end of the day still recognizing that prior appropriations for beneficial uses have the better right.  

To accomplish that goal, there was really only one solution. If groundwater rights – generally junior in priority to surface water rights in the Basin – were to continue to be used, they had to be managed or restricted in a way that mitigated impacts to senior surface water rights. Contemporaneous curtailment of well pumping was less desirable because of the time lag between cessation of groundwater pumping and the increased benefits of streamflow increases. 

Given these considerations, a groundwater cap was selected as the most appropriate solution for the first three years. The amount of that cap, as described in the 2013 Order, was informed by recent historic amounts of groundwater use. The terms of 2013 Order were not appealed.

The change in operations necessitated by the 2013 Order was not without controversy. The State Engineer’s Office fielded several questions about measuring devices, possible ways of pooling groundwater supplies and sensed what could be termed a general tension associated with change represented by the 2013 Order.  But well production reports were filed, adjudications were undertaken, and after three years the 2013 Order had become, if not loved, at least recognized.

Now, with the time to revisit its terms at hand, the information gleaned from those first three years is notable. In particular, the amount of overall groundwater used was significantly below what had been determined at that time to be a reasonable level of use that would not result in injury to senior water rights. Had we seen the full 12 inches applied overall, additional information would be in hand to assess how the interconnected groundwater/surface water system had fared.  Instead, with the equivalent of only about half of the total allotment produced, we are able to conclude only that the groundwater reservoir appeared underutilized compared to what modeling indicated it could withstand.

In total, about 21,000 acre-feet (AF) was reserved for groundwater use under the 12-inch cap.  In the first three years under the 2013 Order, only 10,179 AF was reported as actually pumped.  In essence, roughly 11,000 AF remains in the groundwater system, over and above what would be there had the cap been fully utilized. But it was unavailable to those who needed it and possibly unneeded by those who benefitted from the improved surface water hydrology over those years.

It is clear to me that a more liberal cap should be implemented, at least in the short term. Looking at the data, it appears a cap increase could be used to benefit appropriators with access only to groundwater, and it could be done in a way that respects the amount originally embraced by the 2013 Order’s cap. 

The First Amended Order raises the cap to 15 inches per year. It also allows the carryover of up to 10 inches into the next three-year period. 

The limits under the First Amended Order are intended to allow use of the groundwater source at a level it can sustain under current knowledge.  If the coming period is dry, causing groundwater pumpage to maximize, and learned information reveals injury realized to senior water rights, the Order can be readjusted again in 2020. This adaptive management approach is intended to allow the groundwater portion of the interconnected resource do the most good for the most people, while still respecting its use must be limited in some way for the protection of senior rights.

During preparation of the First Amended Order, I also considered all other comments received following the Feb. 15 public hearing. The First Amended Order reflects that consideration, and its contents are the most appropriate at this time given the current amount of information available. In that regard, I note that groundwater data could be greatly improved if more area groundwater users would consent to provide access to their properties for the collection of that data.  

The First Amended Order will be reviewed after three years of operation thereunder, and new information will be available with which to analyze its effects. 

Thank you for your continued interest in our collective work involving the LaGrange Aquifer and Horse Creek, and for all your help providing needed information.


Patrick T. Tyrrell

Wyoming State Engineer

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