Defining and engineering solutions for agroecological impacts of salinity and waterlogging in an irrigated river valley

Abstract

Through extensive field data collection and finite-difference modeling of groundwater flow, solute transport, and mass balance in the unsaturated zone, salinity and waterlogging problems are investigated in a 50,600 ha study area within an irrigated reach of the Lower Arkansas River Valley in southeastern Colorado. The established data collection program is described and rich data sets, including water table depth, water table salinity, surface water salinity, and soil water salinity are presented for a three-year (1999 - 2001) study period. From these data and other collected or estimated aquifer and unsaturated zone data, models were constructed, calibrated, and tested. The development and application of these models are presented in a series of published articles that are included along with more detailed descriptions of the model components and calibration procedures. These presented components include the unsaturated zone mass balance approach, aquifer recharge estimation, use of geographical information systems (GIS) tools, and special procedures used in the Groundwater Modeling System (GMS version 3.1) interface software to create MODFLOW and MT3DMS models of the investigated alluvial aquifer. The calibrated models were used to investigate a wide range of regional alternatives to mitigate salinization and waterlogging problems. These alternatives incorporated various configurations of solution measures including recharge reduction through increased irrigation efficiency, canal seepage reduction, sub-surface drainage installation, and pumping volume increases. Results indicate that significant reductions in average regional water table elevation (as large as 1.93 m), soil water salinity (up to 950 mg/L), and crop yield increase over the irrigation season can be achieved. Potential for marked reduction in salt loading to the river and in net water consumption was also confirmed. The presented research demonstrates the progression and wide range of activities involved in the irrigation-stream-aquifer modeling process. These activities included field data collection, initial model development, model refinement from the steady-state to transient configuration, creation of an original unsaturated zone mass balance model, model calibration and testing, and model application to investigate proposed solution alternatives.