ALAMOSA — A trial over groundwater regulations for the Rio Grande Basin entered its second week on Monday with Assistant Division Engineer for Colorado Division of Water Resources Division 3 James Heath on the stand.

Heath has been integrally involved in the development and continued refinement of a groundwater model, the Rio Grande Decision Support System (RGDSS), that is an important component of the pending rules and one of the areas at issue in the trial.

Attorneys told Chief District/Water Judge Pattie Swift on Monday that they believed they could conclude the trial by the end of next week, with the state anticipating it could finish its portion of the testimony by the end of this week and attorneys for objectors estimating three days to present their case next week, followed by a day of rebuttal.

Heath described in detail how a peer review team had refined the model from one phase to another as more information and new technology (such as satellite imagery) became available to update and improve the model, which is currently in its sixth phase, with the team already beginning the seventh.

Moving from one phase to the next is continuous, he explained.

The major driver for phase six, he explained, was the 2010 court ruling for Subdistrict #1 to make up for stream depletions starting in 2012.

One of the key purposes for the model, in connection with the groundwater rules, will be the determination of injurious depletions to surface water as a result of groundwater irrigation. This includes groundwater withdrawals not only from farmers and ranchers but also municipal well users and other large well users. The rules require those injurious depletions to be remedied.

Since the first phases of the RGDSS, more information has become available, such as data from well metering as a result of metering rules. Heath said 2009 was the first year those measurements were available.

“That was one of the major pieces of new data we received as part of Phase Six,” he said.

He added, “It challenged our understanding of this water budget process we had historically used … The diversions were significantly less than the estimated pumping we had in our prior phases of the model.”
For example, to save pumping costs irrigators might not use as much water to finish a hay crop as the model would have anticipated.

Heath said the peer review team spent a lot of time analyzing and incorporating new data such as this. The team also enlisted the assistance of local experts such as Agro Engineering to conduct further investigation and analysis, according to Heath.

He stressed that the model was data driven and explained to the judge the types of information that comprised the model ranging from ditch and stream information to types of irrigated crops grown in the San Luis Valley, with more crops added into the model as they became more widely grown in the Valley.

He described tools and terminology in the RGDSS and how the tools were used to develop the model. The data in the current version of the model is from 2010, but phase seven will be incorporating data through 2015. Heath outlined the processes and timelines for incorporating new data, which can take many months.

“There’s quality control and data checks throughout this entire process,” Heath said. “We are reviewing it … to make sure the data is accurate and reliable.”

Heath reviewed numerous memos providing information and recommendations on model refinements. For example, one memo refined the term “groundwater pumping” to “groundwater withdrawals” in order to clarify that free-flowing wells and all other non-exempt wells must comply with the well rules just as much as wells that are mechanically pumped. Other memos dealt with specific geographic areas of the basin or model inputs such as evapotranspiration.

As various memos were brought up Heath repeated that when new information was available and verified as valid, it was implemented into the model.

“When we can implement new data to better inform the model and the science behind it is reliable we do so,” Heath said.