ИСТИНА

Subsurface emitters (SEs) act as line sources with descending Darcian seepage impeded by either natural horizontal bedrock/clayey substratum (Riesenkampf’s scheme) or by designed and constructed barriers, which make a wedge beneath the emitter (an engineered liner) such that deep percolation is avoided and all moisture is funneled up (evapotranspiration). In this paper, an analytical model assumes a tension-saturated steady-state 2D flow (Laplace’s governing PDE) near an emitter, with a capping phreatic line, along which the stream function linearly depends on the horizontal coordinate that allows to use the Polubarinova-Kochina technique, videlicet a conformal mapping of a circular trigon in the hodograph domain on a reference half-plane and ensued solution to the Riemann-Hilbert problem for two holomorphic functions. The position of the free boundary and flow nets are exactly found. In the numerical, finite element model (HYDRUD2D, the Richards-Richardson PDE), a transient initial value problem (giving an asymptotic steady-state limit, which is compared with the analytical solution), is solved in a fixed domain (an isosceles curvilinear tetragon). A vertical cross-section of a lysimeter is a trapezium made of two contrasting porous components with a blanket drain diverting the infiltrated water into a subjacent tunnel, similarly to Kornev’s trench SE, which also acted as a drain. A standard set of HYDRUS computational outputs (isobars, isohumes, streamlines, isotachs) are found, along with the Christiansen uniformity coefficient, which quantifies uniformity of wetting of the topsoil layer. The modelling results guide one in setting SEs which will generate the saturated-unsaturated zone of a “right” wetness. Experimental results in containers with SEs are compared with mathematical modeling results.