A new numerical method to approximate root water uptake fluxes in a mixed-dimensional 1D-3D setting

2021 ◽  
Author(s):  
Timo Koch ◽  
Hanchuan Wu ◽  
Kent-André Mardal ◽  
Rainer Helmig ◽  
Martin Schneider
Keyword(s):  
Analytical Solutions ◽  
Water Pressure ◽  
Numerical Test ◽  
Three Dimensional ◽  
Root Water Uptake ◽  
Richards Equation ◽  
Soil Pressure ◽  
Approximation Accuracy ◽  
Flux Approximation ◽  
Local Water

<p>1D-3D methods are used to describe root water and nutrient uptake in complex root networks. Root systems are described as networks of line segments embedded in a three-dimensional soil domain. Particularly for dry soils, local water pressure and nutrient concentration gradients can be become very large in the vicinity of roots. Commonly used discretization lengths (for example 1cm) in root-soil interaction models do not allow to capture these gradients accurately. We present a new numerical scheme for approximating root-soil interface fluxes. The scheme is formulated in the continuous PDE setting so that is it formally independent of the spatial discretization scheme (e.g. FVM, FD, FEM). The interface flux approximation is based on a reconstruction of interface quantities using local analytical solutions of the steady-rate Richards equation. The local mass exchange is numerically distributed in the vicinity of the root. The distribution results in a regularization of the soil pressure solution which is easier to approximate numerically. This technique allows for coarser grid resolutions while maintaining approximation accuracy. The new scheme is verified numerically against analytical solutions for simplified cases. We also explore limitations and possible errors in the flux approximation with numerical test cases. Finally, we present the results of a recently published benchmark case using this new method.</p>

Analyses of groundwater flow and plant evapotranspiration in a vegetated soil slope

2013 ◽  
Vol 50 (12) ◽  
pp. 1204-1218 ◽  
Author(s):  
A.K. Leung ◽  
C.W.W. Ng
Keyword(s):  
Groundwater Flow ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Root Water Uptake ◽  
Dry Season ◽  
Climatic Data ◽  
Wet Season ◽  
Soil Slopes ◽  
Transient Seepage

Understanding seasonal hydrogeological responses of vegetated soil slopes is vital to slope stability because pore-water pressure (PWP) varies from positive values upon rainfall in wet seasons to negative values upon plant evapotranspiration (ET) in dry seasons. There are, however, few case histories that report seasonal performance of vegetated soil slopes. In this study, a vegetated slope situated in Hong Kong was instrumented to analyse (i) groundwater flow during rainfall in the wet season and (ii) effects of plant ET on PWP in the dry season. Two- and three-dimensional anisotropic transient seepage analyses are conducted to identify groundwater flow mechanism(s) during a heavy rainstorm. Through water and energy balance calculations, measured plant-induced suction is interpreted with plant characteristic and climatic data. During the rainstorm, substantial recharge of the groundwater table was recorded, likely due to preferential water flow along relict joints and three-dimensional cross-slope groundwater flow. During the dry season, the peak suction induced by plant ET is up to 200 kPa and the depth of influence is shallower than 200% of the root depth. For the range of suctions monitored, root-water uptake is revealed to have been restricted by suction not very significantly and was driven mainly by the climatic variation.

Analytical solutions for calculating pore-water pressure in an infinite unsaturated slope with different root architectures

2015 ◽  
Vol 52 (12) ◽  
pp. 1981-1992 ◽  
Author(s):  
C.W.W. Ng ◽  
H.W. Liu ◽  
S. Feng
Keyword(s):  
Pore Water ◽  
Water Uptake ◽  
Analytical Solutions ◽  
Root Architecture ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Root Water Uptake ◽  
Silty Sand ◽  
Wet Season ◽  
Pressure Distributions

Vegetation can reduce pore-water pressure in soil by root water uptake. The reduction of pore-water pressure results in higher shear strength, but lower soil water permeability, affecting slope stability and rainfall infiltration, respectively. Effects of different root architectures on root water uptake and hence pore-water pressure distributions are not well understood. In this study, new analytical solutions for calculating pore-water pressure in an infinite unsaturated vegetated slope are derived for different root architectures, namely, uniform, triangular, exponential, and parabolic root architectures. Using the newly developed solutions, four series of analytical parametric analyses are carried out to improve understanding of the factors affecting root water uptake and hence influencing pore-water pressure distributions. In the dry season, different root architectures can lead to large variations in pore-water pressure distributions. It is found that the exponential root architecture induces the highest negative pore-water pressure in the soil, followed by the triangular, uniform, and parabolic root architectures. The maximum negative pore-water pressure induced by the parabolic root architecture is about 77% of that induced by the exponential root architecture in the steady state. For a given root architecture, vegetation in completely decomposed granite (CDG, classified as silty sand) induces higher negative pore-water pressure than in either fine sand or silt. The zone influenced by vegetation can be about three to six times the root depth. In the wet season, after a 10 year return period rainfall with a duration of 24 h, different root architectures show similar pore-water pressure distributions.

scholarly journals The Hydromechanical Interplay in the Simplified Three-Dimensional Limit Equilibrium Analyses of Unsaturated Slope Stability

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 73
Author(s):  
Panagiotis Sitarenios ◽  
Francesca Casini
Keyword(s):  
Analytical Solution ◽  
Slope Stability ◽  
Slope Failure ◽  
Failure Modes ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Three Dimensional ◽  
Stability Limit ◽  
Smooth Transition

This paper presents a three-dimensional slope stability limit equilibrium solution for translational planar failure modes. The proposed solution uses Bishop’s average skeleton stress combined with the Mohr–Coulomb failure criterion to describe soil strength evolution under unsaturated conditions while its formulation ensures a natural and smooth transition from the unsaturated to the saturated regime and vice versa. The proposed analytical solution is evaluated by comparing its predictions with the results of the Ruedlingen slope failure experiment. The comparison suggests that, despite its relative simplicity, the analytical solution can capture the experimentally observed behaviour well and highlights the importance of considering lateral resistance together with a realistic interplay between mechanical parameters (cohesion) and hydraulic (pore water pressure) conditions.

scholarly journals Analysis of Soil Water Response to Grass Transpiration

2013 ◽  
Vol 1 (No. 3) ◽  
pp. 85-98
Author(s):  
Dohnal Michal ◽  
Dušek Jaromír ◽  
Vogel Tomáš ◽  
Herza Jiří
Keyword(s):  
Soil Water ◽  
Water Uptake ◽  
Preferential Flow ◽  
Water Movement ◽  
Control Volume ◽  
Water Pressure ◽  
Lower Boundary ◽  
Root Water Uptake ◽  
Water Dynamics ◽  
Soil Water Dynamics

This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.

scholarly journals Using Externally Bonded CFRP to Repair a PCCP with Broken Wires under Combined Loads

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Kejie Zhai ◽  
Hongyuan Fang ◽  
Bing Fu ◽  
Fuming Wang ◽  
Benyue Hu
Keyword(s):  
Prestressed Concrete ◽  
Three Dimensional ◽  
Soil Pressure ◽  
Long Distance ◽  
Stress Strain ◽  
Wire Breakage ◽  
Water Pipelines ◽  
Externally Bonded ◽  
Prestressed Concrete Cylinder Pipe ◽  
Three Dimensional Finite Element

Prestressed concrete cylinder pipe (PCCP) is widely used for long-distance water pipelines throughout the world. However, prestressing wire breakage is the most common form of PCCP damage. For some pipelines that cannot be shut down, a new technique for in-service PCCP repair by externally bonding the pipe with layers of carbon fiber reinforced polymer (CFRP) was proposed. A set of three-dimensional finite element models of the repaired PCCP have been proposed and implemented in the ABAQUS software, which took into account the soil pressure, the weight of the PCCP, the weight of the water, and the hydrostatic pressure. The stress–strain features of the PCCP repaired with CFRP of various thicknesses were analyzed. The stress–strain features of different wire breakage rates for the repaired PCCP were also analyzed. The results showed that the strains and stresses decreased at the springline if the PCCP was repaired with CFRP, which improved the operation of the PCCP. It has been found that the wire breakage rates had a significant effect on the strains and stresses of each PCCP component, but CFRP failed to reach its potential tensile strength when other materials were broken.

Three‐Dimensional Numerical Investigation of Pore Water Pressure and Deformation of Pumped Aquifer Systems

Ground Water ◽  
2019 ◽  
Vol 58 (2) ◽  
pp. 278-290 ◽  
Author(s):  
Yun Zhang ◽  
Xuexin Yan ◽  
Tianliang Yang ◽  
Jichun Wu ◽  
Jianzhong Wu
Keyword(s):  
Numerical Investigation ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Aquifer Systems

scholarly journals Numerical simulation of three-dimensional velocity fields in pressurized and non-pressurized Nye channels

2003 ◽  
Vol 37 ◽  
pp. 281-285 ◽  
Author(s):  
Paul D. Bates ◽  
Martin J. Siegert ◽  
Victoria Lee ◽  
Bryn P. Hubbard ◽  
Peter W. Nienow
Keyword(s):  
Water Flow ◽  
Water Pressure ◽  
Three Dimensional ◽  
Experimental Manipulation ◽  
Navier Stokes ◽  
Ice Dynamics ◽  
Theoretical Understanding ◽  
Water Flow Velocity ◽  
Hydraulic Behaviour ◽  
Strong Control

AbstractChannels incised into bedrock, or Nye channels, often form an important component of subglacial drainage at temperate glaciers, and their structure exerts control over patterns and rates of (a) channel erosion, (b) water flow-velocity and (c) water pressure. The latter, in turn, exerts a strong control over basal traction and, thus, ice dynamics. In order to investigate these controls, it is necessary to quantify detailed flow processes in subglacial Nye channels. However, it is effectively impossible to acquire such measurements from fully pressurized, subglacial channels. To solve this problem, we here apply a three-dimensional, finite-volume solution of the Reynolds averaged Navier– Stokes (RANS) equations with a one-equation mixing-length turbulence closure to simulate flow in a 3 m long section of an active Nye channel located in the immediate foreground of Glacier de Tsanfleuron, Switzerland. Numerical model output permits high-resolution visualization of water flow through the channel reach, and enables evaluation of the experimental manipulation of the pressure field adopted across the overlying ice lid. This yields an increased theoretical understanding of the hydraulic behaviour of Nye channels, and, in the future, of their effect on glacier drainage, geomorphology and ice dynamics.

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