Doctoral Student Unraveling Mysteries Of Large-Scale Aquifers

SOCORRO, N.M. July 23, 2010 -- Jesus Gomez hopes his hydrology research will help municipal leaders and scientists better understand how natural and human induced climate variability influence the flow and transport characteristics of groundwater systems.

This article appears in the Summer 2010 issue of The Divining Rod, the quarterly newsletter of the Water Resource Research Institute, based at New Mexico State University.

A doctoral student at New Mexico Tech, Gomez has modeled the complex systems that dictate groundwater flow, specifically to determine the age distribution of water within a regional aquifer.

Jesus Gomez collects temperature data along La Jara Creek in Valles Caldera National Preserve. A New Mexico Tech doctoral student, Gomez’ research examines how climate changes affect the age distribution of water in Southwest aquifers.
Photo courtesy of Jesus Gomez

Under the tutelage of his advisor Dr. John Wilson, Gomez has several projects – both modeling and field work – that attempt to dispel the assumption that groundwater age distributions are static over time.

For his research funded by the WRRI, Gomez simulated a typical large watershed that includes local, intermediate and regional flow paths – paths that vary from hundreds of meters to thousands of kilometers.

Using COMSOL Multiphysics software, Gomez created a hypothetical recharge system that mimics a typical arid Southwest situation. He then ran multiple multi-decade scenarios that included differing climate and weather.

“The factors that influence flow change over time,” he said. “We’re looking at the classic problem in groundwater hydrology: how long has the water that we sample been in the aquifer and where does it come from.”

He bases his work on the theory that in any one aquifer, water of varying ages will commingle – from years old to thousands or millennia old. Over time, an aquifer will recharge at differing rates, largely dependent on variations in climate.

“Essentially, when you take a dip of water, you don’t have one age, but a distribution of ages,” he said. “Maybe 80 percent is 10 years old and 10 percent could be 100 years old and the rest is much older – as one example. What we have observed is that changes in climatic conditions have a strong effect on the age distributions we observe.”

His modeling work has shown fluctuations in seasonal climate changes and in decadal stages. Gomez employs environmental tracers – either natural or introduced tracers – to study flow path and regeneration.

Groundwater flow paths vary greatly in length, depth and travel time from points of recharge to points of discharge in the groundwater system.
Graphic courtesy of the USGS

“We want to improve our interpretation of environmental tracers and understand better and do an assessment of risks in an aquifer,” he said. “We want to understand where water comes from. A lot of decisions about when you take water and how much you pump are based on how long the water is in the system.”

By examining the age of water in an aquifer – and the distribution of various ages – Gomez’ research will help water managers make more informed decisions. His work will help advance the understanding of not just how water flows, but also how contaminants move.

With his WRRI research coming to a close, Gomez and Wilson have embarked on a new field study to examine a much smaller system – a river meander in the Valles Caldera. Funded by the NSF, they are now putting their theoretical work funded by the WRRI to the test. Gomez and his colleagues will use a variety of dating techniques to test water samples. They will examine standard tracers – carbon-14, helium, tritium and stable isotopes of water – to develop a snapshot of the age distribution.

“If you’re looking at a meander or a regional system or the ocean, it’s the same problem,” he said. “How long do things stay in the system. The problem is always the same – the things that drive flow change over time.”

Gomez earned his master’s at New Mexico Tech in 2008 and will complete his doctoral studies in 2011 or 2012. A native of Colombia, he earned his bachelor’s in civil engineering with emphasis on channel hydraulics at the National University of Colombia in Medellin.

He developed an interest in groundwater hydrology because Colombia is mainly dependent on surface water.

“It seemed strange to me that we [in Colombia] don’t use groundwater,” he said. “The issue is that we don’t have the expertise to exploit the resources. This course of study is good for me if I want to return and contribute. … If we have people with knowledge of groundwater hydrology, we can do a better job of using our resources correctly.”

-- NMT --

By Thomas Guengerich/New Mexico Tech