Hydrochemical tracers in the middle Rio Grande Basin, USA: 2. Calibration of a groundwater-flow model

The calibration of a groundwater model with the aid of hydrochemical data has demonstrated that low recharge rates in the Middle Rio Grande Basin may be responsible for a groundwater trough in the center of the basin and for a substantial amount of Rio Grande water in the regional flow system. Earli...

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Bibliographic Details
Published in:Hydrogeology journal 2004-08, Vol.12 (4), p.389-407
Main Authors: Sanford, WardE, Plummer, L.Niel, McAda, DouglasP, Bexfield, LauraM, Anderholm, ScottK
Format: Article
Language:English
Subjects:
Calibration
Flow system
Geological surveys
Groundwater
Parameter estimation
Recharge
Studies
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Summary:The calibration of a groundwater model with the aid of hydrochemical data has demonstrated that low recharge rates in the Middle Rio Grande Basin may be responsible for a groundwater trough in the center of the basin and for a substantial amount of Rio Grande water in the regional flow system. Earlier models of the basin had difficulty reproducing these features without any hydrochemical data to constrain the rates and distribution of recharge. The objective of this study was to use the large quantity of available hydrochemical data to help calibrate the model parameters, including the recharge rates. The model was constructed using the US Geological Survey's software MODFLOW, MODPATH, and UCODE, and calibrated using ^sup 14^C activities and the positions of certain flow zones defined by the hydrochemical data. Parameter estimation was performed using a combination of nonlinear regression techniques and a manual search for the minimum difference between field and simulated observations. The calibrated recharge values were substantially smaller than those used in previous models. Results from a 30,000-year transient simulation suggest that recharge was at a maximum about 20,000 years ago and at a minimum about 10,000 years ago.[PUBLICATION ABSTRACT]
ISSN:1431-2174
1435-0157
DOI:10.1007/s10040-004-0326-4