Middle Rio Grande Basin Study

Neil Plummer and Ward Stanford ( http://nm.water.usgs.gov/mrg )
Links: [Paper] [Presentation - Plummer] [Paper - Sanford]

They talked of the use of chemical and isotopic data to improve understanding of groundwater flow in the Middle Rio Grande basin.

This is a 7800 km2 basin in New Mexico, USA, including a range of physiographic provinces and the Rio Grande Rift. The basin's water has many uses, mainly for irrigation and urban uses. The basin population has increased almost 120% from 1970-2000, now with about 690,000 people.The aquifer is generally unconfined (or semi-confined at depth). Over the past 40 years, water levels have declined more than 40 meters.

Over 6 years, 300 wells and springs were analyzed for several groundwater parameters. Data analysis showed that groundwater generally flows North to South,  revealed locations of groundwater troughs and relations to tectonic faults. Radio carbon analysis estimated most of aquifer water is over 10,000 years old [and thus does not recharge quickly]. These findings brought significant changes to groundwater understanding in this basin.

Thus, chemical and isotopic analysis can improve understanding of the degree of renewability (or non-renewability) of groundwater resources, and thus the severity of water availability in the region.

In conclusion:

• Environmental tracers are an important data source -- in addition to geological water level -- to calibrate regional groundwater models.
• This case study showed that aquifer recharge rate is much less than previously estimated, but was higher in the past, [thus indicating a need for careful management of human withdrawals].

- Júlio Thadeu Kettelhut