Water Flow Model Research Articles

Leaf elongation response to blue light is mediated by stomatal-induced variations in transpiration in Festuca arundinacea.

Reduced blue light irradiance is known to enhance leaf elongation rate (LER) in grasses, but the mechanisms involved have not yet been elucidated. We investigated whether leaf elongation response to reduced blue light could be mediated by stomata-induced variations of plant transpiration. Two experiments were carried out on tall fescue in order to monitor LER and transpiration under reduced blue light irradiance. Additionally, LER dynamics were compared with those observed in the response to vapour pressure deficit (VPD)-induced variations of transpiration. Finally, we developed a model of water flow within a tiller to simulate the observed short-term response of LER to various transpiration regimes. LER dramatically increased in response to blue light reduction and then reached new steady states, which remained higher than the control. Reduced blue light triggered a simultaneous stomatal closure which induced an immediate decrease of leaf transpiration. The hydraulic model of leaf elongation accurately predicted the LER response to blue light and VPD, resulting from an increase in the growth-induced water potential gradient in the leaf growth zone. Our results suggest that the blue light signal is sensed by stomata of expanded leaves and transduced to the leaf growth zone through the hydraulic architecture of the tiller.

On the Numerical Modeling of Water Flows in Porous Media under Near-Critical Conditions

The problem of the numerical modeling of nonisothermal water and vapor flows in a porous medium under near-critical thermodynamic conditions is considered. It is shown that the equations of single-phase and two-phase flows in porous media become degenerate at the critical point of water. Some disadvantages of flow modeling methods that are able to exclude degeneracy by selecting the pressure and enthalpy as independent model variables are discussed. A new method of modeling under near-critical thermodynamic conditions in the standard pressure–temperature variables is proposed. This method is based on an approxinate description of the fluid phase diagram with linear splines that eliminates the degeneracy of conservation laws at the critical point and enables the application of equations of state for predicting the fluid properties in pressure and temperature variables.

Last-decade progress in understanding and modeling the land surface processes on the Tibetan Plateau

Abstract. Land surface models (LSMs) that simulate water and energy exchanges at the land–atmosphere interface are a key component of Earth system models. The Tibetan Plateau (TP) drives the Asian monsoon through surface heating and thus plays a key role in regulating the climate system in the Northern Hemisphere. Therefore, it is vital to understand and represent well the land surface processes on the TP. After an early review that identified key issues in the understanding and modeling of land surface processes on the TP in 2009, much progress has been made in the last decade in developing new land surface schemes and supporting datasets. This review summarizes the major advances. (i) An enthalpy-based approach was adopted to enhance the description of cryosphere processes such as glacier and snow mass balance and soil freeze–thaw transition. (ii) Parameterization of the vertical mixing process was improved in lake models to ensure reasonable heat transfer to the deep water and to the near-surface atmosphere. (iii) New schemes were proposed for modeling water flow and heat transfer in soils accounting for the effects of vertical soil heterogeneity due to the presence of high soil organic matter content and dense vegetation roots in surface soils or gravel in soil columns. (iv) Supporting datasets of meteorological forcing and soil parameters were developed by integrating multi-source datasets including ground-based observations. Perspectives on the further improvement of land surface modeling on the TP are provided, including the continuous updating of supporting datasets, parameter estimation through assimilation of satellite observations, improvement of snow and lake processes, adoption of data-driven and artificial intelligence methods, and the development of an integrated LSM for the TP.

Assessing an efficient hybrid of Monte Carlo technique (GSA-GLUE) in Uncertainty and Sensitivity Analysis of vanGenuchten Soil Moisture Characteristics Curve

Studying model uncertainty and identifying the parameter uncertainty in the modeling of water flow through the soil is useful to improve water and soil management. This research aimed to assess the uncertainty of the parameters of soil water retention curve (SWRC) models using an efficient hybrid of the Monte Carlo technique e.g. generalized likelihood uncertainty estimation (GLUE). GLUE estimates the parameters of vanGenuchten, vanGenuchten-Mualem, and vanGenuchten-Burdine models for four soil classes. Also, to evaluate the relative importance of the model parameters, generalized sensitivity analysis (GSA) was performed. The results of the uncertainty analysis showed that among the studied models, the vanGenuchten-Mualem model with the indices of S = 0.05, T = 0.4, d-factor = 0.25 and, PCI = 100 was considered as the most accurate model with the least uncertainty. Also, the results of GSA were demonstrated that alpha and n parameters were sensitive parameters in the models. Consequently, identifying the uncertainty of the SWRC model structure and its parameters, relevant models with higher accuracy can be used in the study of soil water processes, and better water resource allocation.

How to relevantly characterize hydraulic properties of saline and sodic soils for water and solute transport simulations

Proper sets of soil hydraulic parameters are important for modeling water flow and solute transport. Using field saline water and laboratory tap water, this study systematically analyzed and compared laboratory saturated hydraulic conductivity, Kls and soil water retention curve, SWRC of saline soil within three soil multi-layered profiles to find out the adequate initial hydraulic parameter set of a hydrological model. Falling and constant head methods were applied on three undisturbed samples per pedogenic horizon. SWRC were established on the same samples, using both saline and tap water. Results showed the spatial variability of hydraulic properties in vertical and horizontal dimensions when comparing soil profiles' properties. The constant head method with saline water resulted in the highest Kls values followed by the falling head method with saline water, the constant head method with fresh water, and the falling head method with fresh water. The differences in Kls were up to two orders of magnitude when comparing all datasets. Fresh water reduced soil water retention significantly. A significant correlation between the hydraulic properties and some physical and chemical properties suggests that the effects of soil texture, structure, calcium carbonate and gypsum content, and CEC (clay mineralogy) were larger than those of salt content. The change in hydraulic properties and the dependency on the procedure use may be attributed to aggregate breakdown and plugging of macropores, clay heterogeneity and dispersion, calcium carbonate and gypsum dissolution, all damaging soil structure. Simulation runs illustrated that hydraulic properties obtained with saline water resulted in better model performance than when using the conventional procedures with fresh/tap water. A proper set of initial hydraulic parameter values is an important step in model calibration and thus must be characterized correctly. Therefore, to hydraulically characterize saline soil, procedures should be standardized. Moreover, the approach and results of this study may provide a reference for characterization of soil hydraulic properties of saline and sodic soils effectively.

Numerical modeling of post-flood water flow in pavement structures

Water infiltration through pavement structures as a result of flooding and/or extreme rainfalls, can adversely influence the bearing capacity of the pavement and lead to its premature failure. Since the entire pavement system will not be always in saturated state, the post-flood water movement throughout its granular layers should be formulated based on unsaturated flow principles. This study is aimed at developing a practical numerical model for simulating the partially saturated water flow in pavements caused by surface infiltration. To this end, available numerical methods and software packages are evaluated based on the relative merits of availability and computational rigor. The selected method is validated with published data. Existing correlations are used to reduce the number of inputs required for modeling. Subsequently, a parametric study is carried out to investigate the influence of material properties, such as aggregate gradation, and environmental conditions, such as rainfall intensity and duration, on the pavement’s response. Special cases, such as anisotropic material and clogged drainage are also modeled. This study provides an insight into the hydraulic behavior of pavement structures subjected to severe precipitation. In addition, this model establishes a solid basis for subsequent structural analyses to fully understand the behavior of inundated pavements under traffic loadings.

Salt stress reduces root water uptake in barley (Hordeum vulgare L.) through modification of the transcellular transport path.

The aim of the study was to understand the hydraulic response to salt stress of the root system of the comparatively salt-tolerant crop barley (Hordeum vulgare L.). We focused on the transcellular path of water movement across the root cylinder that involves the crossing of membranes. This path allows for selective water uptake, while excluding salt ions. Hydroponically grown plants were exposed to 100 mM NaCl for 5-7 days and analysed when 15-17 days old. A range of complementary and novel approaches was used to determine hydraulic conductivity (Lp). This included analyses at cell, root and plant level and modelling of water flow. Apoplastic barrier formation and gene expression level of aquaporins (AQPs) was analysed. Salt stress reduced the Lp of root system through reducing water flow along the transcellular path. This involved changes in the activity and gene expression level of AQPs. Modelling of root-Lp showed that the reduction in root-Lp did not require added hydraulic resistances through apoplastic barriers at the endodermis. The bulk of data points to a near-perfect semi-permeability of roots of control plants (solute reflection coefficient σ ~1.0). Roots of salt-stressed plants are almost as semi-permeable (σ > 0.8).

Modeling and optimization of a chilled-water cooling system with multiple chillers

In order to reduce energy consumption of the centralized chilled-water cooling system in large buildings, a dynamic control strategy was proposed for cooling plants by modelling and optimization. Combined with the chilled water flow model, this paper analyzed the parallel operation characteristics of the chillers and takes the load distribution as one of the control parameters. Based on the measured data of a typical cooling system that has undergone preliminary energy-saving transformation, the residual neural network is applied to model the relationship among energy consumption, controllable parameters and environmental parameters, and the residual neural network outperforms multi-layer perceptron and support vector regression. To minimize the total energy consumption, the gray wolf optimizer was introduced to optimize the controllable variables of the cooling system. Compared with the energy consumption before optimization, the simulation energy consumption after optimization decreased 10.45% on average, while the energy saving rate is only 7.9% with equal chilled water supply temperature of parallel chillers.

Experimental study and numerical simulation of dam reservoir sediment release

In this research, experimental and numerical modelling of three-phase air, water, and sediment transport flow, due to the opening of a sluice gate was conducted in two scenarios, i.e., with and without a triangular obstacle. Numerical simulation was conducted using the Navier-Stokes equations with the aid of the volume of fluid method (VOF) to track the free surface of the fluid. For the experimental model, a glass-enclosed flume with 150 × 30 × 50 cm dimensions was used. The experiment was performed for an initial height of the water column at 20 cm and 10 cm sediment column. To evaluate the numerical model's performance, the simulation results were compared with the experimental observations using the average relative error %. The amount of relative error between experimental observations and numerical simulations, for the position and height of the wave flow for the three-phase air, water, and sediment flow, were obtained as 2.64% and 4.51% for the position and height of the water wave, and 2.23% and 2.82% for the position and height of the sediment transport, respectively, for the ‘without obstacle’ scenario, and 3.77% and 5.25% for the position and height of the water wave, and 2% and 7.23% for the position and height of the sediment transport, respectively, for the ‘with obstacle’ scenario. The findings of the study indicate the appropriate performance of the numerical model in the simulation of water and sediment wavefront advance, and also its weakness in the estimation of wave height.

Peridynamics modelling of coupled water flow and chemical transport in unsaturated porous media

A wide range of phenomena in natural or engineered systems emerge from strongly coupled hydraulic, chemical and mechanical processes involving a mix of clearly discrete and quasi-continuous mechanisms. Non-local formulations of these processes, e.g. based on Peridynamics, offer significant advantages compared to classical local formulations. Existing Peridynamics models for water flow and chemical transport are applicable only to saturated systems and use loosely coupling schemes, such as explicit time stepping approaches. This work advances the non-local approach by developing a bond-based formulation for coupled water flow and chemical transport in partially saturated porous media. An implicit solution is proposed for coupling the PD formulation of chemical transport with water flow formulation. Firstly, the proposed formulation is verified against results from finite element/finite difference transient solutions for 1-D and 2-D coupled problems. The agreement between results demonstrates the accuracy of the proposed methodology. Secondly, a series of case studies are presented to illustrate the model’s capability to capture discontinuities and heterogeneities, including stationary cracks, propagating cracks, and randomly distributed permeable and impermeable inclusions. The results show that the multi-physics Peridynamics-based formulations and computational model (Pyramid) provide clear advantages to classical local formulations for analyses of reactive transport in partially saturated porous media with physically realistic microstructures.

Numerical Modeling of Surface Water and Groundwater Interactions Induced by Complex Fluvial Landforms and Human Activities in the Pingtung Plain Groundwater Basin, Taiwan

The landforms and human activities play important roles in quantifying surface water and groundwater interactions (SGIs) for water resources management. The study uses the groundwater and surface water flow (GSFLOW) model to quantify the dynamics of SGIs in the Pingtung Plain groundwater basin (PPGB) in southern Taiwan. Specifically, the study uses a physical-based numerical model to quantify the spatial and seasonal variations of water cycles influenced by complex fluvial landform conditions and human activities. Results of the model calibrations show good agreement with the data obtained from the available groundwater monitoring network and the selected stream stations. The basin-scale water budgets show highly nonuniform precipitation in the study area, and over 80% annual precipitation is from wet seasons in the PPGB. With high permeable surficial deposits in the PPGB, the year-averaged surface runoff and infiltration are approximately 57% and 40% of the total precipitation. The fluvial landforms with the high slope in the PPGB lead to 70% of annual surface runoff that becomes the streamflow, and the interflow dominates water interactions near streambeds. Results show that the interflow rate in the wet seasons is 200% more than that in the dry seasons. The net groundwater discharge to the streams is relatively small as compared to the interflow. Only 10% of the river flow is from the net groundwater discharge. In the PPGB, The pumping-induced variations of groundwater levels are insignificant as compared with the factor of the natural landforms. Because of the relatively small area of the proposed artificial lake, the contribution of the artificial lake on the local water budgets is insignificant, indicating the low impact of the artificial recharge lake on the surface water environment.

Geometrically intrinsic modeling of shallow water flows

Shallow water models of geophysical flows must be adapted to geometric characteristics in the presence of a general bottom topography with non-negligible slopes and curvatures, such as a mountain landscape. In this paper we derive an intrinsic shallow water model from the Navier–Stokes equations defined on a local reference frame anchored on the bottom surface. The equations resulting are characterized by non-autonomous flux functions and source terms embodying only the geometric information. We show that the proposed model is rotational invariant, admits a conserved energy, is well-balanced, and it is formally a second order approximation of the Navier–Stokes equations with respect to a geometry-based order parameter. We then derive a numerical discretization by means of a first order upwind Godunov finite volume scheme intrinsically defined on the bottom surface. We study convergence properties of the resulting scheme both theoretically and numerically. Simulations on several synthetic test cases are used to validate the theoretical results as well as more experimental properties of the solver. The results show the importance of taking into full consideration the bottom geometry even for relatively mild and slowly varying curvatures.

Effects of nanopore geometry on confined water flow: A view of lattice Boltzmann simulation

Water flow in nanoscale channel is demonstrated to be affected by the robust water-wall interactions, including that the flow significantly deviates from the conventional continuum flow. As suggested in different results of experimental observation and simulation in recent literature, nanopores exhibit higher/lower-than-expected flow capacity. Most existing studies are limited to simple geometry that displays a circular cross-section. However, the flow dynamics of water in noncircular pores significantly deviates from the Hagen–Poiseuille flow equation adopted in circular pores that exhibit different contact angles and dimensions. In this study, molecular interactions between water and the solid inner wall are substituted into the formulations of the Lattice Boltzmann method to simulate the flow dynamics in nanopores that exhibit different cross-sectional shapes and wettability. The results show that, under identical cross-sectional area injection pressure, the circular nanopore exhibits the maximum flow capacity. In terms of a circular cross-sectional shape, the constant density lines are also circular and concentric. For angular cross-sectional shape, the constant density lines do not comply with the cross-sectional shape, and the density varies significantly at the corner. The effects of geometry and density distribution of different contact angles are elucidated. An empirical formula under different geometry and wettability has been established, which is of high significance in modeling water flow in various engineering nano-systems such as shale matrix, membrane, and aquaporins.

MILP and MINLP models for the optimal scheduling of multi-energy systems accounting for delivery temperature of units, topology and non-isothermal mixing

Multi-Energy Systems (MES) represent an increasingly important element in the undergoing energy transition, as they can effectively supply different energy vectors to their users through the coordinated local management of a set of different energy sources. This work presents an innovative Mixed Integer Linear Programming (MILP) formulation for the operational planning of MES featuring thermal generators arranged in series and/or parallel with different and/or variable heat delivery temperatures and filled-tank thermal energy storages. The proposed model can approximate the non-isothermal mixing processes occurring in water collectors and storage systems through the definition of a set of virtual headers at constant temperature levels. To assess the accuracy of the MILP model (called water-flow MILP), a detailed MINLP model of the MES is formulated (water-flow MINLP). The two models are compared with the energy-flow MILP model adopted in the literature (neglecting details of the internal MES arrangement and supply temperatures), considering a set of real-world case studies consisting in different possible MES designs designed to serve the District Heating Network of our university. Results indicate how literature energy-flow models tend to underestimate operating costs by as much as 16% and define an operational solution not able to reach the target heat delivery temperature. The proposed linearized water-flow MILP model allows to identify scheduling solutions which are not only feasible but also equal or better than the solutions found by solving the MINLP model. For MES with multiple dispatchable units (e.g., CHP engine, heat pumps and boilers), the MINLP model cannot be solved to global optimality within 1 h while the MILP water flow model can find feasible solutions with 6% lower cost.

A multi-model approach for analysing water balance and water-related ecosystem services in the Ouriyori catchment (Benin)

ABSTRACT Freshwater supply remains limited in West Africa due to lack of operational governance frameworks. In this study, the Water flow and balance Simulation Model (WaSiM) and the Soil and Water Assessment Tool (SWAT) were applied in the Ouriyori catchment (14.5 km2, Benin) to assess hydrological ecosystem services (HES) in terms of service flow and service capacity using the ecosystem accounting framework. The modelling exercises indicated satisfactory goodness-of-fit coefficients greater than 75% with an absolute bias of less than 25%. The HES capacity was in general higher than the HES flow for crop and household (surface/groundwater) water supplies, indicating that the catchment can potentially supply more water under optimal storage and management conditions. Positive and negative shifts in service capacities of crop water and household supplies were observed over the simulation period. These significant results can support sustainable interventions in securing water and food productions through increasing HES flow and capacity.

Effect of Climate Change on a Monolithic Desulphurized Tailings Cover

A soil cover system can be viewed as a thin interface placed between the atmosphere and the underlying waste. Climate is a primary design variable in soil cover design; therefore, climate change poses a number of challenges to design, operation and long-term performance of covers. In this research climate change effects on the hydraulic behavior of soil covers at a Northern Ontario, Canada site were assessed. Covers were analyzed using historical and future climate datasets. Historical climate data were compiled from an Environment Canada weather station near the site. The future climate datasets were sourced for different Global Circulation Models (GCM) for various representative concentration pathways (RCP). The covers at the site were constructed with a single layer of desulphurized tailings. Soil covers were meant to limit oxygen ingress to the underlying reactive tailings by maintaining high water saturation in the covers. Oxygen flux through soil covers for current and future climates were predicted using variably saturated water flow and oxygen transport modeling using the finite element method. The results of this research indicate that the effect of climate change on soil cover depends on the hydraulic properties of the soil cover materials and that of the underlying tailings. The results of this study suggest that the effect of climate change on the coarse tailing covers could be marginal resulting in a maximum increase of 5% in oxygen flux at the cover surface for the future climates in comparison to the base climate. However, in the case of fine tailings covers, increases of up to 65% can be expected.

Some multiple flow direction algorithms for overland flow on general meshes

After recalling the most classical multiple flow direction algorithms (MFD), we establish their equivalence with a well chosen discretization of Manning–Strickler models for water flow. From this analogy, we derive a new MFD algorithm that remains valid on general, possibly non conforming meshes. We also derive a convergence theory for MFD algorithms based on the Manning–Strickler models. Numerical experiments illustrate the good behavior of the method even on distorted meshes.

Optimization of Irrigation and Leaching Depths Considering the Cost of Water Using WASH_1D/2D Models

Optimization of water use with consideration of salinity control is a crucial task for crop production. A new scheme, “optimized irrigation”, was recently presented to determine irrigation depth using WASH_1D/2D which are numerical simulation models of water flow and solute transport in soils and crop growth. In the scheme, irrigation depth is determined such that net income is maximized considering the price of water and weather forecasts. To evaluate whether the optimized irrigation is also able to restrict salinity stress and avoid salinization without any intentional leaching, we carried out a numerical experiment for winter wheat grown in northern Sudan under the following scenarios: (1) Available water in the root zone is refilled using freshwater (0.17 g/L of NaCl) at every five days; (2) available water in the root zone is refilled using saline water (1.7 g/L) at every five days; (3) optimized irrigation using fresh water at 7-days interval; (4) optimized irrigation on a weekly basis using saline water; and (5) same as scenario 2, except for leaching is carried out at the middle of the growing season and leaching depth is optimized such that net income is maximized. The results showed that the optimized irrigation scheme automatically instructs additional water required for leaching at each irrigation event and maximizes the net income even under saline conditions.

Transport characteristics of non-cohesive sediment with different hydrological durations and sediment transport formulas

River sediment transport is an important global environmental issue, for it leads to waterway sedimentation, ecological degradation, and river geomorphologic evolution, its quantification is of the highest importance for river and watershed management. However, it remains unclear what the applicability of different sediment transport formulas in sediment transport process, and what the characteristics of non-cohesive sediment transport processes with different hydrological durations. This study developed a two-dimensional (2D) surface water Flow Model (FM) coupled with a Sediment Transport (ST) model in the MIKE 21 modelling system. The characteristic difference on simulated non-cohesive sediment transport under different sediment concentrations, hydrological durations, and sediment transport formulas were quantified by calculating the bed load, suspended load, and bed level change. Results indicated that the bed load and suspended load using the Engelund and Fredsøe formula were significantly lower than the Van Rijn formula for individual rainfall simulation scenarios. With the increase in peak flow, both suspended load and bed load first increased and then decreased. In the long-term duration simulations, high sediment concentrations were accompanied by higher bed load and lower suspension load for the Engelund and Fredsøe formula, but by lower bed load and suspension load for the Van Rijn formula. The high sediment concentrations resulted in a higher erosion rate, and low sediment concentrations resulted in a higher deposition rate. The two formulas had a high degree of consistency in seasonality and the bed level changes in spring and summer were mainly sedimentary, while in autumn and winter they were mainly erosive. The Engelund and Fredsøe formula produced high riverbed erosion capacity at low discharge, but the Van Rijn formula had high erosion capacity at high discharge.

Small differences in root distributions allow resource niche partitioning.

Deep roots have long been thought to allow trees to coexist with shallow‐rooted grasses. However, data demonstrating how root distributions affect water uptake and niche partitioning are uncommon.We describe tree and grass root distributions using a depth‐specific tracer experiment six times over two years in a subtropical savanna, Kruger National Park, South Africa. These point‐in‐time measurements were then used in a soil water flow model to simulate continuous water uptake by depth and plant growth form (trees and grasses) across two growing seasons. This allowed estimates of the total amount of water a root distribution could absorb as well as the amount of water a root distribution could absorb in excess of the other rooting distribution (i.e., unique hydrological niche).Most active tree and grass roots were in shallow soils: The mean depth of water uptake was 22 cm for trees and 17 cm for grasses. Slightly deeper rooting distributions provided trees with 5% more soil water than the grasses in a drier season, but 13% less water in a wetter season. Small differences also provided each rooting distribution (tree or grass) with unique hydrological niches of 4 to 13 mm water.The effect of rooting distributions has long been inferred. By quantifying the depth and timing of water uptake, we demonstrated how even small differences in rooting distributions can provide plants with resource niches that can contribute to species coexistence. Differences in total water uptake and unique hydrological niche sizes were small in this system, but they indicated that tradeoffs in rooting strategies can be expected to contribute to tree and grass coexistence because 1) competitive advantages change over time and 2) plant growth forms always have access to a soil resource pool that is not available to the other plant growth form.