Steady Water Flow with Interacting Point Source–Point Sink–Water Table in a Cylindrical Soil Domain

Abstract

Core Ideas Simultaneous root water uptake from a surface emitter and from groundwater is evaluated. The source–sink–water table problem is decoupled into source–sink and sink–water table problems. Water uptake from the surface emitter is larger in the presence of a shallow water table. Water uptake from a shallow water table is smaller if applying supplementary irrigation. A previously derived analytical solution to the quasi‐linear form of the water flow equation is used to analyze (i) steady, coupled plant water uptake from a surface water emitter in a confined cylindrical soil domain with a non‐evaporating surface in the presence of a shallow water table, and (ii) water uptake from only the water table in the absence of a surface emitter. Illustrative examples serve to analyze and discuss water‐uptake rates of a subsurface, spherical, conceived root zone and the complex water‐flow patterns occurring in either natural fields with shallow groundwater or artificial lysimeters. The coupled source–sink–water table model is also used to illustrate the dependence of the contributions of surface emitter and water table to the overall water‐uptake rate on capillary length and hydraulic conductivity of the saturated soil, the depth of the water table and its prescribed pressure head, the depth and size of the root zone, and the radius of the confined cylinder, representing the effect of neighboring plants and emitters. The proposed methodology can be used to evaluate the effects of these factors on the potential utilization of shallow groundwater, as well as in cases with a supplementary drip irrigation system, and to support design decisions concerning the distance between emitters (and between plants) and the irrigation rates required to complement plant water uptake from groundwater.