SACRAMENTO MOUNTAINS WATERSHED STUDY: A WATERSHED-SCALE INVESTIGATION OF THE HYDROLOGIC RESPONSE TO TREE-THINNING

Water resources in New Mexico, and other arid regions of the southwestern United States, are important for local communities and land-owners. Concern over water availability has highlighted the need for land use and water management practices that can sustain existing water resources. The Sacramento Mountains, in southeastern New Mexico, are the recharge area for local aquifers, and adjacent regional aquifers, including the Roswell Artesian Basin and the Salt Basin. Tree thinning, which is being implemented in the Sacramento Mountains as a forest restoration technique, has been suggested for increasing local groundwater levels and spring discharge by reducing canopy interception loss and net transpiration. The Sacramento Mountain watershed study aims to assess effects of tree thinning in a small watershed on the local hydrologic system.

This study takes place on a forested, 800 acre watershed east of Cloudcroft, NM. Thinning of 400 acres was completed in 2011. The forest type in the area is mixed conifer. Stratigraphy consists of thin loam and clay loam soils overlying fractured bedrock of the San Andres and Yeso Formations.

We are using a soil water balance to estimate potential recharge to the groundwater system before and after application of the thinning treatment. Data collection during post-treatment monitoring includes measurement of groundwater levels, spring discharge, soil moisture, precipitation and other climate data that will help to estimate the different components of the water balance.

Calculation of the distributed soil water balance is performed under a GIS framework using a regularly spaced grid of 30x30 meter cells. Calculation of the water balance is performed at a daily time-step. Preliminary results indicate that soil moisture increases after thinning due to a decrease in canopy interception and net transpiration. However, upward hydraulic gradients in the soil indicate an increase in soil water evaporation from increased incident solar radiation.