​By Clayton Palmer

For two decades, the Colorado River Storage Project Management Center Marketing office has sponsored the development of a model with an interesting name: Generation and Transmission Maximization, or the GTMax.

Starting with monthly water volumes, the GTMax optimizes the hourly electrical power generation of the four large CRSP dams simultaneously for as many months or years as is useful. 

This model is used to develop the CRSP preschedule, to test improvements in power optimization, to consider the power impact of drought and other externally derived conditions, to forecast the cost of firming purchases and to aid CRSP customers, federal agencies and others to better understand how WAPA works. 

In December 2010, the secretary of the interior announced that the department would propose to change the operation of Glen Canyon Dam and begin the preparation of an environmental impact statement, or EIS.  

CRSP MC soon sought status as a cooperating agency, declaring that it deserved this position because WAPA’s legal authorities included the transport and marketing of electrical power from Glen Canyon Dam and because it had the experience and expertise to perform the hydropower analysis that would be necessary for the EIS. 

Also, it had the GTMax and the experienced technical staff that could use it. 

In the beginning 

In the late 1980s, WAPA was ordered by a federal court to prepare an EIS on WAPA’s marketing of CRSP power. 

CRSP MC worked with Argonne National Laboratory to develop a simple spreadsheet model to simulate the hydropower operation of the CRSP dams. The essence of an EIS, and the order from the court, was to evaluate and compare a broad set of alternative marketing schemes and operations of the CRSP dams for power production. 

Some sort of model was required that could evaluate the effect of the alternative hourly production patterns of hydropower and water release from CRSP dams. 

On WAPA’s behalf, Argonne invented a simple spreadsheet model: the Hydro LP.  The model has since grown in sophistication and precision; it now models all CRSP units simultaneously. It’s not limited to linear solutions and it runs very quickly. 

Argonne copyrighted the GTMax model and sells it commercially. WAPA’s CRSP office uses a souped-up version of the model: the GTMax Superlite. Two CRSP MC employees are GTMax Superlite modelers and several analysts at Argonne are experts in the model and available to write new code and modify the model as new needs and challenges present themselves. 

Beyond simulating the operation of the CRSP dams, the GTMax model can be used to optimize, within constraints, the hydropower production at the CRSP power units.  

CRSP MC’s Operations office in Montrose, Colorado, uses the output of the model to create the daily preschedule of dam operations. The model maximizes power output to meet scheduled load from firm electric service customers within the operational constraints and water availability of the CRSP dams. 

“This model has made our analysis much easier for preparing the CRSP operations schedule we send to Reclamation, and also for preparing our seasonal purchase analysis,” said Supervisory Public Utilities Specialist Chrystal Dean. “We plug into GTMax the water volume that Reclamation needs us to release for the month and, within a few seconds, we have an hourly release schedule for the month or months we are interested in.” 

Tricky situations

CRSP MC uses the GTMax model in tricky environmental situations. In 2006, fishing guides working on Green River below Flaming Gorge worried that WAPA’s winter-season schedule – following changes in electrical demand during the day – was destroying the sport fishery. Reclamation’s Upper Colorado regional director even sent a letter instructing WAPA not to use Flaming Gorge to follow electrical load until things could get worked out. 

CRSP MC Environment staff began meeting with the Green River fishing guides group and fish biologists from the State of Utah.  

They used the GTMax model to develop example release patterns to demonstrate to state biologists and fishing guides alternative release patterns that would meet electrical demand and be accommodating to sport fish. This allowed WAPA to satisfy the state and the fishing guides that the organization’s release pattern was not hurting the fish, and it resulted in saving or avoiding an estimated $2 million in costs.

“Flaming Gorge is tricky to plan,” said Dean. “I prepare releases from Flaming Gorge Dam for power purposes, but we also have to make sure those releases fit within the requirements of gage restrictions 108 miles downstream from the dam. Given the complexities of tracking flowing water downstream, there is no way we could accomplish it. But GTMax does.”

CRSP MC’s Rates and Finances offices use the GTMax Superlite to estimate future purchase power expenses. 

The GTMax model takes information on sets of alternative hydrological scenarios from a Reclamation water-routing model and calculates years, months and hours in which CRSP generation will be short of customers’ firm electrical obligations. It then calculates a cost of market purchases to meet shortages.

This is done for as many years as the Rates office needs to conduct its power repayment study.  

“The GTMax model gives us realistic and credible estimates of firming purchase expense over whatever time period we need,” said Public Utilities Specialist Thomas Hackett. “Because of the credibility of the model, our expense numbers are easy to defend and we keep our firm power rate as low as possible knowing that we’re not just guessing about the future.” 

In addition, these firming purchase expenses are given to the CRSP MC Finance office, which uses them to estimate the balance of funds in the CRSP Basin Fund. 

“The Basin Fund is the operating funds for CRSP,” said Financial Officer Tyler Nelson. “We don’t receive appropriations. We have to make sure our Basin Fund balance is sufficient to pay our salaries and operating expenses every year.”  

Wider benefits

CRSP customers are also familiar with the GTMax model and take advantage of WAPA’s ability to study how they will fare in certain circumstances. 

“We’ve worried about the Colorado River drought that started in 2000,” said Leslie James, executive director of the Colorado River Energy Distributors Association. “It’s been 20 years of hydrological conditions that have not been wet enough to refill Lake Powell. CRSP MC staff has used the GTMax model to estimate the cost of firming power and the subsequent effect on the rate that would occur if the drought continues. That’s really helpful for our planning for worst-case conditions.”

Reclamation, which sponsored the development of a sophisticated water-routing model for the Colorado River System, can only estimate hydropower production by month. This model, widely used by Reclamation and considered critical by western water districts and others who have an interest in the analysis Reclamation produces, is the Colorado River System Simulation model.  

“The monthly water releases produced by the CRSS model are what we use as inputs to the GTMax model,” said Management Analyst Jerry Wilhite. “From there, our model estimates hourly electrical production for each month, for each of the CRSP powerplants for all of the years we need to have estimates for.”  

Because GTMax makes use of Reclamation’s CRSS model, it can be run over a wide range of hydrological scenarios. CRSP MC staff can estimate hydropower production as easily for a series of droughts as for a string of years of average water.

Reclamation also believes that the GTMax model is the way to get a credible measure of CRSP hydropower production. 

To date, the GTMax has been used by CRSP MC and by Reclamation to evaluate the hydropower energy production and value for the set of alternatives in environmental impact statements for the operation of Flaming Gorge Dam, the set of Aspinall Dams, the joint operation of Lake Powell and Lake Mead and, most recently, the operation of Glen Canyon Dam. 

“An accurate and credible CRSP power simulation model is key to understanding our power system, getting the most out of it and opening the door to other federal agencies who can affect how Reclamation operates the CRSP dams,” said Administrative and Technical Services Manager Brian Sadler. “The market and environmental conditions are always in flux. Fortunately, we have solid access to the people who wrote this program and we can constantly make changes to it to meet our current needs.”   

Note: Palmer is an environmental protection specialist.

Last modified on September 12th, 2023