New Mexico Geological Society Annual Spring Meeting — Abstracts

There is widespread interest in removing trees to increase water yields in southern New Mexico. The Sacramento Mountain watershed study focuses on: 1) characterization of water budgets of a mixed conifer forested watershed in the Southern Sacramento Mountains, NM; 2) assessment of the effects of tree thinning on the watershed hydrologic system; and evaluation of total watershed surface and groundwater outflows. Pre-treatment analyses have been used to develop a conceptual model of the hydrogeologic system within the study area and to identify inputs and outputs to the local water budget.

Taking place within the bounds of a broader regional study, this project addresses two spatial scales: the 750 acre Three L Canyon watershed and 90x90m study plots. The watershed is located on private property near James Canyon approximately 20 km east of Cloudcroft. There are two springs in Three L Canyon, but no perennial streams that transport water outside the watershed. Elevations within the study area range from 2300 to 2600 m above sea level. Tree densities in the study area average 312 trees/acre, with Douglas-fir being the most common species. Thinning slated to begin in fall 2010 will reduce the average tree density to 40 – 60 trees/acre.

Well logs from three observation wells were used to characterize the subsurface geology. Measurements begun in mid-2008 include field surveys, soil and water chemistry analyses, and automated sensor data. Automated data collected from multiple sites include: spring discharge, valley groundwater levels, soil moisture, matric potential, canopy throughfall, and precipitation and climate data.

Well logs, groundwater level data, and geochemical data indicate a complex multilayered groundwater system. Chloride and stable isotope profiles in soils suggest rapid movement of water through the thin rocky soils, indicating high infiltration rates and low runoff. Spring hydrographs, stable isotope data, and water chemistry suggests that discharge from the two springs largely comes from outside of the watershed and are therefore considered to be inputs. Other inputs include local precipitation and inflowing groundwater. Outputs include evapotranspiration, and both shallow and deep groundwater flow.