Modeling Subsurface Heterogeneity of Irrigated and Drained Fields. I: Model Development and Testing

Abstract

Efficient management of irrigation/drainage systems relies to a large extent on the ability to predict a priori the response of the system to a proposed management plan. However, such numerical prediction of system response (e.g., root-zone hydrosalinity conditions and crop yield) are dependent on several parameters that are spatially and/or temporally variable and are related to soil properties, atmospheric conditions, crop type, and the amount and salinity of water application. This paper presents enhancements to the Colorado State University Irrigation And Drainage (CSUID) model that expand its capacity to fully simulate the dynamics of variably saturated flow and transport in a three-dimensional (3D) variably saturated porous media and to account for spatial and temporal heterogeneity in input parameters. The CSUID model has the ability to simulate irrigation/drainage activities and their impact on the soil and underlying groundwater, as well as on crop yield, taking into account the spatial and temporal variability in available soil moisture, including matric stress, waterlogging, and osmotic stress due to salinity. Having a model with these capabilities is an important step towards understanding the influence of heterogeneous inputs and parameter uncertainty on the design and management of field-scale irrigation/drainage systems. Four benchmark problems are used in this paper to test the CSUID model and the model performs well. In addition, an example is presented to demonstrate model capabilities in representing a 3D time-varying irrigated field with and without subsurface drainage.