New Mexico Geological Society Annual Spring Meeting — Abstracts

Fasong Yuan and Seiichi Miyamoto (2004) published a paper that demonstrated a negative correlation between chloride concentration on the Rio Grande measured at El Paso, TX and the Pacific Decadal Oscillation (PDO). By analyzing historical data they concluded that the chloride concentration at El Paso is largely determined by the mount of stream discharge in the Middle Rio Grande Basin that is associated with the PDO. They did not explore in their paper the effect of Elephant Butte Reservoir (EBR) on the PDO signal at El Paso, nor did they offer an explanation for the correlation of chloride concentration with discharge.

We have analyzed chloride and discharge data from the Rio Grande above EBR at San Marcial in order to determine the influence of EBR on the PDO signal at El Paso. We compared data from 1950 to 1980 when the reservoir level was low, and data from 1980 to 1990’s when reservoir level was high, to the PDO index. We determined firstly, that the PDO signal is detectable at San Marcial and secondly, that EBR serves to dampen, rather than enhance, the PDO signal at El Paso when the reservoir level is high.

Furthermore, we have concluded that during times when the PDO index is negative and discharge in the river is low chloride is likely stored in the vadose zone and shallow groundwater of the agricultural system in the RG Basin, and then is flushed out when the PDO index increases and discharge is higher.