Well owners, water agencies, conservationists and others with an interest in how and where water flows need to tell scientists their needs and goals so that modeling of complex systems such as aquifers can better inform policy decisions, said a leading hydrologist who spoke Thursday in Angels Camp.

All too often, organizations develop single models and cling to those models when they and the public would be better served by developing and testing many different models, said University of Arizona professor Ty Ferre.

“If your model is so complicated you can’t afford to run it many, many times to reduce uncertainty, then your model is too complicated,” Ferre said.

Ferre’s appearance in the multipurpose room at Bret Harte High School is one of 100 talks he will make at sites around the world this year as 2016’s Distinguished Darcy Lecturer. The National Groundwater Association each year chooses a top scientist in the field to serve as the Darcy Lecturer and tour the world spreading information about the science behind hydrology.

The honor is named for Henry Darcy, a French engineer whose efforts in the 1850s to solve water problems for the city of Dijon led to several important advances in the science of hydraulics.

Ferre chose to expand the audience for his tour beyond scientists to include policy- makers and members of communities with stakes in decisions about issues such as regulating wells or managing river systems.

The topic is particularly timely in California now as the state develops a regulatory framework to attempt to halt the over-drafting of groundwater supplies.

John Kramer, a hydrogeologist at Condor Earth Technologies in Sonora, collaborated with Calaveras County Supervisor Debbie Ponte to have a visit to Calaveras County added to Ferre’s speaking tour. Kramer said that the Butte Fire raised awareness of how vulnerable watersheds here are to catastrophic change, making Ferre’s message timely.

The approximately 20 people in the audience for Ferre’s talk included Ponte, Sean Kriletich of Calaveras Grown, Bret Harte High School science instructor Keith Maurer, and Columbia College water sciences instructor Steve Christianson, as well as three students from a water utility introductory course Christianson teaches at Calaveras High School.

On Friday, Ferre also met in San Andreas with Calaveras County government staff members involved in water issues and paid a visit to a physics class at Calaveras High School. Earlier on Thursday, Ferre also spoke at Columbia College in neighboring Tuolumne County.

During Thursday night’s talk, Ferre explained the challenges facing hydrologists. First, water systems are incredibly complex, depending on weather patterns, soil types, the hidden geology of rock formations and aquifers and the behavior of millions of humans who take water from those systems.

In contrast, models are always simplified mathematical representations of those systems. Many different models are always possible for any given system, reflecting different variables that may be included and different assumptions about the relationships between those variables. Variables could include factors such as rainfall in a given year, how much water users pump from wells, changes in surface water flows as a result and the rise or fall of groundwater levels.

One issue that sometimes arises with modeling is that rival interests – say well owners in a watershed versus those taking water from surface sources – can hire scientists to make competing models. Both models may be consistent with available data, but they may emphasis different issues and reach different conclusions about the likely result of particular policy decisions, Ferre said.

Rather than fighting over which model is correct, Ferre said scientists should test many different models and consider the valid interests of the various parties involved. He described what he called “utility curves” that reflect the perceived value of a particular outcome – such as more water for surface users, or more pumping by well owners – from the perspective of those interest groups.

Those utility curves, in turn, can help scientists to find where they need to focus on data collection. That’s important because collecting data is expensive. Agencies can only afford to drill so many monitoring wells or install so many river level gauges.

By using computers to run thousands of different models thousands of times and considering the utility curves, scientists can determine which models are likely to be useful and which data to collect that will be most likely to resolve public policy debates, Ferre said. His research team has focused on this issue and developed methods to reduce research costs.

A member of the audience asked Ferre if this kind of analysis could be useful to inform debates over managing water storage behind dams. Often, large federal agencies release water and reduce storage for goals such as preserving flood control capacity or protecting endangered fish species. This puts those agencies at odds with local water agencies that would rather hold more water behind the dams for use by farms and cities

Ferre’s answer: “Yes.” And, he noted, some agencies, such as the Army Corps of Engineers, are not very flexible about crafting models that reflect the goals of other interests even as those interests may lack the capacity to do their own scientific analysis.

“We often don’t have someone on the other side who has done the utility curve,” Ferre said.

You can track Ferre’s progress on his lecture tour and read highlights of questions and answers from those events online at darcylecture2016.wordpress.com.

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