Assessment of Long‐Term Salinity Changes in an Irrigated Stream‐Aquifer System

Abstract

Changes in salinity in groundwater and surface water in the Arkansas River valley of southeastern Colorado are primarily related to irrigation practices. A solute transport model was applied to an 11-mile reach of the valley to compute salinity changes in response to spatially and temporally varying stresses. The model was calibrated in 1973 using detailed field measurements made during 1971 and 1972. In 1973 the calibrated model was used to predict that a gradual long-term increase in groundwater salinity of about 2-3% per year would occur if the observed irrigation practices continued. The study area was resampled during the winter of 1982 to help evaluate if any long-term changes in salinity are actually occurring. Nonparametric and parametric statistical tests were used to help assess the significance of observed changes in groundwater salinity. These tests indicate that a statistically significant increase in salinity occurred between the winters of 1971 and 1972 (the model calibration period). However, a comparison of the winter 1972 and winter 1982 data indicates that no significant net change in salinity has occurred during this 10-year period. An analysis of the few available historical data (1895, 1923, 1959-1961, and 1964) supports the hypothesis that groundwater salinity in this irrigated area has reached a long-term dynamic equilibrium in response to irrigation practices. The model predictions of long-term salinity increases were invalid probably because the calibration period occurred during a short-term annual trend of increasing salinity in the river (and hence in leaky irrigation canals and in applied irrigation water), which was not representative of the long-term trend. Thispaper is not subject to U.S. copyright. Published in 1985 by the American Geophysical Union. Paper number 5W0640. quality variations within an irrigated stream-aquifer system in southeastern Colorado. Hydrologists and soil scientists have placed considerable emphasis on studying the relationship between agricultural practices and water quality variations in irrigated streamaquifer systems. Recognition of the cycle of water application, consumptive use, deep percolation, and return flow to the river has led to hydrosalinity modeling efforts to consider solute and water transport within all parts of irrigated streamaquifer systems. Hornsby [1973], in his review of hydrosalinity modeling, presents several conceptual diagrams for various subsystems that may be represented within irrigated streamaquifer systems, as well as for various physicochemical processes that act within each subsystem. • •Al•though numerous modeling studies have successfully predicted changes in water quality within some or all parts of irrigated stream-aquifer systems, model results have usually been compared with field data sampled over short periods of time and/or within small study areas due to economic and practical constraints [Tanji, 1981]. Increased salinity caused by irrigation practices, however, may take years to be noticed. Most studies that ha...

Combined Estimation of Hydrogeologic Conceptual Model, Parameter, and Scenario Uncertainty with Application to Uranium Transport at the Hanford Site 300 Area

“…Given our knowledge of the potential importance of hydrogeologic uncertainties and their categorization as conceptual model, parameter, or scenario uncertainty, Comments Error Phoenix (Konikow 1986) Assumed past groundwater pumping would continue in future Scenario/ Conceptual Cross Bar Ranch Wellfield (Stewart and Langevin 1999) Assumed a 75-day, no-recharge scenario would represent long-term maximum drawdown Scenario/ Conceptual Arkansas Valley (Konikow and Person 1985) Needed a longer period of calibration Scenario/ Parameter Coachella Valley (Konikow and Swain 1990) Recharge events unanticipated Scenario INEL (Lewis and Goldstein 1982) Dispersivities poorly estimated Parameter Milan Army Plant (Andersen and Lu 2003) Extrapolated localized pump test results to larger area Parameter Blue River (Alley and Emery 1986) Storativity poorly estimated Parameter/ Conceptual Houston (Jorgensen 1981) Including subsidence in model improved predictions Conceptual HYDROCOIN (Konikow et al 1997) Boundary condition modeled poorly Conceptual Ontario Uranium Tailings (Flavelle et al 1991) Inadequate chemical reaction model Conceptual…”

Process-based groundwater salinisation risk assessment methodology: Application to the Akrotiri aquifer (Southern Cyprus)

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