New Mexico Geological Society Annual Spring Meeting — Abstracts

Groundwater recharge in New Mexico not only largely defines a limit for water availability in this semiarid state, but also is the least understood aspect of the state’s water budget. With the goal of estimating groundwater recharge statewide, we are developing the Evapotranspiration and Recharge Model (ETRM), which uses existing remote sensing spatial datasets to model the daily soil-water balance over the state at a resolution of 250 x 250 m. The model, as currently configured, estimates only diffuse recharge over the landscape, not focused recharge from channels or playas.

We require runoff data to calibrate and test ETRM’s simulations. As runoff data from ephemeral channels are sparse in NM, we have turned to the US Agricultural Research Service Walnut Gulch Experimental Watershed (WGEW) in southern Arizona, which is one of the most densely gauged and monitored semiarid rangeland watersheds for hydrology research. Runoff is calculated as Hortonian overland flow in ETRM, and it is one of the major sinks in the soil-water balance. This runoff, though not tracked through space in the model, is the source water for focused recharge, which can be estimated by transmission loss in ephemeral channels. By using the precipitation and runoff data from WGEW, we can relate rainfall intensity and antecedent soil moisture to the amount of measured runoff and subsequent channel infiltration. We will ultimately employ stochastic analytical theory to generate improved runoff estimates for ETRM based on simulated soil-water balances from ETRM and on generalized precipitation datasets.