Infiltration Studies

Infiltration Scenario for the Pajarito Plateau, Northern New Mexico

A map of net infiltration for the Pajarito Plateau, Northern New Mexico, was created for the pre-Cerro Grande fire period using new and previously published estimates of point infiltration in upland areas as well as estimates of stream flow losses and gains along canyon bottoms. The point infiltration estimates are based on a combination of techniques that include the use of the Richards’ equation, the chloride mass balance method, and numerical modeling.

The infiltration rates estimated with these techniques were extrapolated to uncharacterized parts of the study area using maps of environmental variables, which were correlated with infiltration and spatial algorithms implemented with GIS software using the mapped variables. This map indicates that infiltration rates on mesas of the Pajarito Plateau are generally less than two millimeters per year (mm/yr), except near faults. Infiltration rates at higher elevations in the Sierra de los Valle are typically greater than 25 mm/yr in mixed conifer areas and greater than 200 mm/yr in areas vegetated by aspen. An irregular transition zone with infiltration rates between 10 and 25 mm/yr exists near the western edge of the Pajarito Plateau adjacent to the Sierra de los Valle. Canyon bottom infiltration rates are highly variable, ranging from several hundred mm/yr to several mm/yr. The total net infiltration of approximately 8,600 acre-feet per year is consistent with estimates of the steady state of groundwater discharge to perennial streams in the study area.

Limitations of the study are that it does not address the effects of the Cerro Grande fire on the hydrology of the study area, nor does it completely capture the complex and sometimes incompletely documented history of laboratory-generated discharges during its 60-year history.

Surface Geology for the Los Alamos Regional Infiltration Study Area

Geology shown for the Los Alamos infiltration study area was created by carefully matching and then combining regional scale as well as local site scale geologic models of different resolutions. The dashed box represents the boundary between the two models. The surface geology shown is used as one layer of input into a study of surface water infiltration rates in the region surrounding the Los Alamos National Laboratory. The geology shown is a combination of a coarse resolution regional geologic model and a finer resolution model more focused on the Los Alamos National Laboratory.

Both models received the same legend classification with symbols intended to create an appearance that is easy to look at while maximizing the contrast between adjacent units to aid in identifying boundaries. Geologic interpretation is further enhanced by the overlay of a semitransparent hillshade along with drainage channels and fault lines. Canyon names, transportation infrastructure, and the study unit boundary are added to assist in defining the locations of units of interest.

The intended use of these maps is for illustration purposes only. All other uses are disclaimed. Neither the U.S. Government nor the University of California or any of their employees makes any warranty, expressed or implied, including the warranties of merchantability and fitness for a particular purpose, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that their use would not infringe privately owned rights.