New Mexico Geological Society Annual Spring Meeting — Abstracts

This study, funded by the Taos Soil & Water Conservation District, is a follow up to the findings of the NMBGMR OFR 581, published in 2016 by Johnson, Bauer and Felix. They reported (1) a decline in water levels between 2011 and 2015 in the southern Taos Valley; (2) a severe water level drop measured in the West Romero Road area; and (3) postulated fault barriers to groundwater recharge. New water level measurements made in 2017 in the West Romero Road area show that the water-level decline bottomed in winter 2014. The time of declining water level is within the 1993-2014 drought, as recorded at the nearby Taos airport, at NRCS SNOTEL stations in the headwaters of the Sangre de Cristo Mountains, and by declining stream flows at the Rio Pueblo de Taos gage. However, the lack of normal precipitation since August 2017 and winter 2018 indicate a resumption of drought conditions. Wells that were drilled as far back as 1975 requiring OSE well permits and being located accurately by GPS in the 2000’s had static water levels reported both high and low to recent measurements for various reasons. A water table elevation map, which used well water levels measured in the 2011-2017 period and contoured on a 10-foot contour interval, shows regional variations in both water level and recharge sources. Major recharge sources include Rio Pueblo de Taos, Rio Grande del Rancho, several acéquias, and some arroyos. Seasonal groundwater levels change less than one foot within a half mile of rivers. Seasonal changes near acéquias vary from one foot to over five feet. The West Romero Road area has a high water table elevation from recent recharge from the Rio Grande del Rancho and the Llano Quemado acéquia, but probably is among the first to lower during a drought. Small groundwater highs underlie many arroyos and probably are derived from occasional local flash floods. Multiple deeper aquifers that vary in extent and permeability can have either short-term fast or longer-term slow recharge. Upwelling warm waters along fault zones and changing pressure gradients add to water-table changes. The four major Los Córdovas faults and their branches locally appear to interrupt the groundwater level. These faults, which are visible in outcrop of alluvium north of Rio Pueblo de Taos, deepen southward under the southern Taos Valley and might be offset by east-west trending Picuris faults. The intersection of the Los Córdovas and Picuris faults, which is suggested by high resolution aeromagnetics, probably has produced fault-compartmentalized blocks that are likely to also have contributed both to water-level changes and to water geochemistry differences within aquifers. Other factors that might be affecting the substantial water table drop in the West Romero Road area include (1) limited downward infiltration from the Llano Quemado acéquia during drought, (2) variable supply of water from major rivers, and (3) excessive field and garden irrigation. Long-term solutions to declining groundwater levels include roof-rainwater harvesting, acéquia improvements and development, and construction of arroyo infiltration dams and ponds.