Modeling Regional Flow and Flow to Drains

Abstract

Flow paths to drain laterals are needed to identify local flow to drains and regional flow. This paper describes the depths at which the flow paths of the regional aquifer‐flow system and the local saturated ground‐water‐flow system separate in a field with 15 drain laterals. The finite difference ground‐water computer model MODFLOW was used to create a transient, two‐dimensional ground‐water‐flow model. Seventy‐eight piezometers were installed at various depths in the field for use in model parameter estimation and to calibrate the model. The hydraulic‐head distribution and advective velocity vectors up to 20 days after a flood irrigation event were modeled. Results confirm that the irrigation water mixes with the shallow ground water and that there is a significant downward flux of water after an irrigation event that reverses with time to a dominant lateral flow with some upward flux of regional‐water flow from a depth of 1–1.5 m below the drain laterals.