Numerical simulation of water flow in tile and mole drainage systems

Abstract

International audienceTile drainage systems are sometimes not sufficient to provide favorable unsaturated conditions in the rootzone. These drainage systems then need to be supplemented with an additional high conductivity material in the trenches above the tiles or by implementing mole drainage. The HYDRUS (2D/3D) model was used to evaluate the impact of such additional measures for heavy clay soil. Three types of drainage systems were simulated: (i) tile drains, (ii) tile drains with gravel trenches, and (iii) tile drains with gravel trenches and mole drains, using either two-dimensional (the former two systems) or three-dimensional (the latter one) transport domains. Three scenarios were considered to test the efficiency of each system: (i) time to drain an initially saturated system, (ii) high intensity rainfall, and (iii) a real case scenario. Different horizontal spacings between tile drains with or without gravel trenches were also compared with the system which included mole drainage. The results showed that the drainage system that included mole drains and gravel trenches was the most efficient. This system provided the largest drainage rate, was the first to reach steady-state in the time to drain scenario, and also efficiently reduced surface runoff. Adding mole drains to a system with tile drains and gravel trenches resulted in a large reduction of surface runoff (75%). Simulations showed that the spacing of tile drains with or without gravel trenches would have to be 40% or 55% smaller, respectively, in order to reproduce the same water table levels as those observed for the drainage system with mole drains. Therefore, introducing mole drains in drainage systems is an efficient practice for reducing waterlogging and runoff

Impacts of Subsurface Tile Drainage on Age—Concentration Dynamics of Inorganic Nitrogen in Soil

“…At the surface lateral boundaries, free‐flow boundary conditions are implemented while at the subsurface lateral boundaries, we use no‐flow boundary conditions. For the bottom boundary condition, since the total soil depth used in this study is 1.6 m, it is unrealistic to define an impermeable bottom soil layer as generally used to simulate tile drainage systems (Buyuktas et al, ; Dusek et al, ; Gerke et al, ; Filipovic et al, ; Mohanty et al, , ). We therefore used free flow at the bottom boundary with 0.1% of the saturated hydraulic conductivity of that used in the soil layers.…”

“…These are considered as birth processes, and the time elapsed since a nitrogen molecule of any chemical species such as nitrate, ammonia, or ammonium enters the soil through any of these mechanisms is its age (Woo & Kumar, , ). While studies have documented the role and impact of tile drains as rapid conduit for loss of nitrogen to receiving water bodies resulting in adverse environmental impacts (Buyuktas et al, ; Dusek et al, ; Filipovic et al, ; Gentry et al, ; Gerke et al, ; Mohanty et al, ; Sands et al, ), little is Known about how they shape the spatial heterogeneity of concentration and age of nitrogen through the soil column. This heterogeneity is further modulated by topographic variability, such as the presence of microtopographic depressions (Le & Kumar, ; Woo & Kumar, ) where ponding creates additional hydraulic head that increases nitrogen transport and reduces mean age by moving younger molecules from near surface to deeper layers.…”

Analyzing subsurface drain network performance in an agricultural monitoring site with a three-dimensional hydrological model

“…Three-dimensional (3D) hydrological models can explicitly describe the different branches of the drainage network and topographical variations in the area, and the resulting lateral flow processes such as water redistribution due to groundwater flow (e.g. Rozemeijer et al, 2010;Turunen et al, 2013Turunen et al, , 2015aTurunen et al, , 2015bFilipović et al, 2014;Warsta et al, 2013aWarsta et al, , 2014. Alternatively, drainage network can be presented adequately e.g.…”

Using System Dynamics for Simulating Subsurface Drainage Systems in Clay Soils

“…These systems are usually installed in irrigated arid and semi arid Journal of Water Resource and Protection lands to control water logging and salinity. The successful performance of a drainage system depends on optimal design of drain depth and drain space [3].…”