Hydrologic Systems Models

Work continued on the development of new conceptual and mathematical models that describe how dynamically changing flow conditions influence the distribution of residence times in hydrologic systems. This work is motivated by the use of natural and manmade tracers (e.g., isotopes) to understand the circulation of water in hydrologic systems and its sensitivity to climate variability and change, and to understand related biogeochemical processes. Models were developed for small-scale (1-100 m) hyporheic exchange and larger scale (1-100 km) basin flows, and demonstrated for dynamic flows ranging from individual storm events up to seasonal, decadal, and longer time scales. Talks were given at several national meetings, including the annual meeting of the American Geophysical Union (AGU), and at various EPSCoR meetings. Grad student Jesus Gomez co-organized a special session at AGU "Groundwater-surface water interactions: Dynamics and patterns across spatial and temporal scales," working with colleagues from the University of Nevada, Reno, and three other U.S. and European universities. The methods will be tested this next two years with data collected in several of the study areas below. The results have implications for atmospheric science and oceanography, not just hydrology.

We continued the development of watershed models for the Valles Caldera and the Rio Hondo using the GS Flow approach (http://water.usgs.gov/nrp/gwsoftware/gsflow/gsflow.html) developed by the US Geological Survey. Most watershed models give little attention to groundwater, treating it simply if at all. The GS Flow approach combines PRMS, a surface water and land surface model, together with MODFLOW, a groundwater model, to develop an integrated model of the entire system. With our emphasis on the role of groundwater in mountain hydrology such an approach is essential, and GS Flow approach provides software and partners (at the U.S. Geology Survey in Carson City, NV, and collaborators in the Nevada EPSCoR project) to pursue this with minimal new software development. Spatial and temporal data sets for the Rio Hondo model have been assembled to provide the input information needed by GSFlow.

An important element for watershed models that includes three-dimensional groundwater is where to draw the boundaries. Surface water divides are conventionally used for boundaries in surface water models, but groundwater divides do not necessarily underlie surface water divides and can move over time. Two models of the Rio Hondo are being examined. One assumes that the surface watershed defines the boundary of the entire 3D model. The other moves the boundary further out to the stream in adjacent valleys (e.g., Red River for the Rio Hondo model). This approach is being examined with simple generic models that explore alternative boundary locations, including the surface water divide, the next adjacent stream, and the next ridge. This summer two journal manuscripts are under development that describe the results of this research, some of which was presented at the Tri-State Meeting.

Working with the Water Quality Group, we made substantial progress in two areas: 1.) The development and instrumentation of a meander study area (see below) along the East Fork of the Jemez River, in the Valles Caldera National Preserve; and 2.) A modeling approach for the transport and reaction of dissolved organic matter (DOM) in hyporheic zones. The site at the Valles Caldera National Preserve is aimed at the investigation of hyporheic exchange between a stream and aquifer. A mathematical simulation model of the meander area was also developed and used to design and interpret field observations and experiments. Preliminary observations, and a description of the study site, were presented in poster presentations at EPSCoR meetings.

DOM is composed of thousands of different, complex organic molecules that react abiotically and biotically as they move through groundwater. To deal with this large and changing population of molecules we settled on an "agent based modeling" approach. By selecting the correct set of rules the model can mimic sorption and microbial mediated transformation, as parameterized and validated through laboratory experiment and field observation. To allow the agents to move, we selected "lattice Boltzmann modeling," which simulates transport processes at the porous media pore scale or, through upscaling, can be used to simulate transport at the aquifer scale (e.g., a meander bend hyporheic zone). Presentations were given at EPSCoR meetings and at the Fall Meeting of AGU.


Several new models have been developed in light of new discoveries in the circulation of water in hydrologic systems and its sensitivity to climate change. Other models are currently being examined, refined, and redefined. The results have implications for atmospheric science and oceanography, not just hydrology.


Due to the use of natural and manmade tracers such as isotopes, new conceptual and mathematical models are being made that describe how changing flow conditions influence the distribution of residence times.

Source: Dr. John Wilson, New Mexico Tech
Image provided by: Natalie Willoughby, NM EPSCoR, University of New Mexico, nawilloughby@gmail.com
Image caption: Dr. John Wilson (NMT) & Graduate student Jevon Harding (NMT) at the Valles Caldera National Preserve