Two-dimensional surface water flow simulation of basin irrigation with anisotropic roughness

Simulating basin surface water flow with anisotropic roughness has practical significance. Based on the complete hydrodynamic model, a two-dimensional surface water flow model of basin irrigation with anisotropic roughness was developed in this study by constructing an anisotropic roughness model in the source terms of the governing equation. Then, the simulation performance of the proposed model was analyzed and compared based on typical experiments of basin irrigation. The results show that with basin surface anisotropic roughness, the proposed model can successfully simulate water flow in basin irrigation, and exhibits better simulation performance than the model with isotropic roughness. Three basin geometries and two kinds of inflow geometries were selected for the application of the proposed model. Applied results show that the anisotropic roughness can improve irrigation performance. When the basin width becomes narrow, the physical effect of the rotation angle in the anisotropic roughness model weakens, even becomes smooth. The two-dimensional surface water flow model of basin irrigation with anisotropic roughness provides a good numerical simulation tool for designing and evaluating the performance of basin irrigation system.     

A one-dimensional complete hydrodynamic model of border irrigation based on a hybrid numerical method

A numerical model of border irrigation flow is a useful tool in the design and evaluation of surface irrigation systems. A one-dimensional complete hydrodynamic numerical model of border irrigation was established by using the time–space hybrid numerical method. Differences in stability, convergence, precision, and efficiency of the one-dimensional model were analyzed and compared between the hybrid numerical method proposed here and the Roe finite-volume method. At the same time, the computational performance and simulation effects were validated based on the results of typical border irrigation tests. The results show that the hybrid numerical method provides better numerical stability and convergence with little water quantity-balance and average relative errors than does the Roe finite-volume method. The computational efficiency is about two times higher under the same measurement circumstances. The proposed model of border irrigation can increase computational stability and convergence, can improve computational precision and efficiency, and can provide a good numerical simulation tool for the design and evaluation of border irrigation systems.     

Simulation of border irrigation system using explicit MacCormack finite difference method

The hydrodynamic, zero-inertia and kinematic wave models for simulating all phases of the border irrigation event are presented. The explicit second-order accurate MacCormack method is used for solving the governing equations. A technique for implementing the boundary conditions that are consistent with the numerical scheme is discussed. All the three models do not require a special treatment such as moving grid, deformable grid, subgrid technique, etc., to accurately simulate the advancing and receding fronts. The results of all the three models namely hydrodynamic finite difference model (HDFD), zero-inertia finite difference model (ZIFD) and kinematic wave finite difference model (KWFD) are compared with observed advance and recession times for four border irrigation events available in literature. A very good comparison of results is observed. The relative merits and demerits of the models are discussed. The HDFD model is found to be more suitable for simulation of all the four phases of border irrigation events.     

撒施肥料一维畦灌地表水流与溶质运移模型构建与验证

模拟撒施肥料下的一维畦灌地表水流与溶质运移过程可为采用先进的畦灌液体施肥方式提供对比依据。该文基于湍流理论垂向流速线性与对数分布规律及不可压缩流体力学连续方程,构造沿畦长及任意垂向断面的非均布流速场和溶质浓度场,建立起撒施肥料下的一维畦灌地表水流与溶质运移模型,并利用典型畦灌施肥试验结果,检验该模型的模拟效果。结果表明,建立的模型不仅具有在撒施肥料状况下较好模拟地表水流运动和溶质浓度时间变化过程的能力,还具备较佳的水量和溶质质量守恒性,从而为评价撒施肥料下的畦灌施肥系统性能及与其它施肥方式下的畦灌施肥系统性能对比,提供了实用的数值模拟工具。     

Comparison and selection of furrow irrigation models

The capability of hydrodynamic, zero-inertia, kinematic-wave and volume-balance models to predict advance and recession phases in furrow irrigation were compared against two sets of field data, providing a wide range of soil conditions and field slopes. The input parameters required for each model were studied, and a simple sensitivity analysis was performed for field slope, furrow geometry, roughness coefficient, infiltration constants, time step, and discharge. The accuracy of the models' predictions depends on the precision of the measurements and the estimation of the input parameters. Excellent prediction of the advance and recession phases were obtained with hydrodynamic, zero-inertia and kinematic-wave models. Those models therefore are preferred in design and management in furrow irrigation.     

畦灌灌水要素决策服务系统

根据精细灌溉的要求,采用零惯量模型和土壤入渗理论,开发建立了可进行畦灌水流运动模拟、灌水质量评价、灌水技术参数优化、利用灌溉试验资料率定糙率和入渗参数等功能的畦灌决策计算机服务系统,该系统可为灌区技术人员确定畦灌技术参数、指导灌水实践提供决策服务,也可作为科研人员研究节水灌溉的一种技术工具。     

Zero-inertia model for surge flow furrow irrigation

Summary A surge flow furrow irrigation model was developed based on the zero-inertia concept originally developed by Strelkoff and Kastapodes, (1977) for border irrigation and later modified for continuous furrow irrigation by Elliot et al. (1982). The model simulates all phases of continuous and surge flow irrigation including simultaneous advance and recession and can also be applied to basin and border irrigation with various field slopes. The surge model was verified for a wide range of actual field conditions and management alternatives. A sensitivity analysis was performed for the size of time step and the physical input parameters.     

Evaluation of infiltration measurements for border irrigation

A number of methods are discussed for obtaining a reasonable estimate of the infiltration function for irrigation borders. Data from ring infiltrometers are fit to power functions for infiltration rate and cumulative infiltration rate versus time and to a branch function where the infiltration rate is not allowed to go below some value (called the final infiltration rate). A volume balance within the border is used to adjust the data to give a better indication of the “average” infiltration conditions over the border. The results of Bouwer's method, which uses a series of borders as infiltrometers, were compared to the results of ring data for actual field data. Bower's method was also analyzed by developing advance and recession curves with the zero-inertia border-irrigation model with a known infiltration rate. The zero-inertia model was also used to examine the effect of different infiltration functions for specific examples (resulting from different irrigations or different estimation methods) on the application of water by surface irrigation.     

Basin irrigation design with longitudinal slope

The aims of this paper are to analyze theoretically the influence of the longitudinal slope of a surface irrigation field on the uniformity of irrigation and to provide practical tools to design, analyze and manage surface irrigation systems with longitudinal slope and blocked end. An example is shown where a 20% savings in water is obtained by giving the field the optimal slope.In 1982, Clemmens and Dedrick published a practical set of dimensionless graphs to level-basin design and analysis (with no slope). This article generalizes those graphs taking account the existence of field slope. So, Clemmens and Dedrick's graphs are a particular case of obtained results.The analysis is based on solving one-dimensional free surface Saint-Venant equations including infiltration, applying the dimensional analysis to reduce the number of variables involved. Saint-Venant equations are solved with the finite differences method, applying the full hydrodynamic model and the zero-inertia model. Two computer programs are used: WinSRFR and POZAL (a specific software that calculates the optimal cutoff time).The result is a set of three-dimensional graphs that show the relationships of field slope, irrigation uniformity and the rest of the involved dimensionless variables, related to infiltration parameters, Manning roughness coefficient, cutoff time, inflow rate and field length and width. The graphs could be useful in practice to determine the optimal slope of a field, the inflow rate or the length and width of a field, achieving substantial savings of water in surface irrigation.     

Drainage disposal and reuse simulation in canal irrigated areas in Haryana

Nearly 60 per cent of the geographical area of Haryana state in Indian Union is underlain by saline ground water. The intra-basin transfer of surface water in the early sixties for irrigation has disturbed the hydrodynamic equilibrium resulting in waterlogging and salinization in large parts of the state. The existing inland drainage basin conditions did not permit the disposal of drainage effluent. The reuse system was therefore, integrated with the drainage system. A model RESBAL was coupled with the calibrated and validated on-farm water management model FAIDS and run for eight years to optimally design a series of connected reservoirs for the disposal of drainage effluent from an area provided with a subsurface drainage system. The possibility of the reuse of the disposed water for irrigation, aqua culture and salt harvesting was also studied comprehensively in order to maintain proper salt balance in the root zone.     

Numerical computation of surface irrigation

A mathematical model based on the complete hydrodynamic equations describing open-channel flow is developed for simulation of a complete irrigation in a surface irrigation system. An explicit two-step numerical scheme has been employed for the solution of the flow equations. The total infiltrated water depth at each location along the field is determined. From this intermediate result three performance parameters, expressing the merits of the irrigation as affected by the magnitude of each of the various independent physical or management variables involved in the process, are evaluated. Through an analysis of these effects the selection of the proper size or magnitude of a number of the major parameters becomes possible and thus an optimum combination of the main design or operation parameters in a surface irrigation system can be obtained. Two examples of the proposed technique are included as well as some typical graphs of standardized solution.     

灌溉施肥地表水流与溶质运移模拟研究进展

采用数值模型能够方便快速地探讨不同灌溉施肥条件下的水肥利用效率,为改善灌溉施肥系统性能、减轻不当灌溉施肥方式对生态环境造成的负面影响提供科学依据。从灌溉施肥地表水流运动模拟、灌溉施肥地表水流溶质运移模拟、灌溉施肥地表水流与溶质运移耦合模拟等方面出发,系统总结了不同时空尺度下灌溉施肥地表水流与溶质运移模拟模型的类型及其相...     

Analysis of basin irrigation performance with variable inflow rate

Basin irrigation systems were designed for a constant flow rate. The operation of the designed system was simulated using the zero-inertia model of surface irrigation. The performance of the system was obtained for modified design flow rates. Three patterns of flow variation — sinusoidal, initially low then high, and initially high then low — were studied. The average of a variable flow rate in a given simulation equalled, was less than and greater than the design flow rates. The flow rate variations did not lower the performance of the system when the average flow rate during irrigation was greater than or equal to the design flow rate. Significant reductions in system performance occurred when the average flow rate was equal to 50% of the design. Basin irrigation systems should be designed for the average of the variable flow rate available at the field outlet.     

二维撒施畦灌地表水流溶质运移模型：II验证

基于撒施施肥方式下畦灌试验数据,从传统平均相对误差和马尔科夫随机过程两个角度,对二维撒施畦灌地表水流溶质运移模型进行了验证．基于传统平均相对误差的结果表明,模型模拟的水流推进与消退的平均相对误差分剐为4．98％和9．37％,水量平衡误差为0．28％,模拟各测点的溶质质量浓度变化过程平均相对误差为8．64％-14．22％,溶质平衡误差O．58％,构建的模型不仅具有较好的模拟二维撒施畦灌地表水流运动和溶质质量浓度变化过程的能力,还具备较佳的水量与溶质质量守恒性．基于马尔科夫随机过程的计算结果表明,地形项的随机性对模拟效果的影响为88．68％-96．21％,而畦面土壤物理属性等模型未能考虑因素的随机性对各测点溶质质量浓度变化的影响为3．79％-11．32％,因此仅考虑畦面微地形分布随机性的模型,具备优良的二维撒施畦灌地表水流和溶质运移过程的模拟性能．构建的模型为评价撒施施肥方式下的畦灌施肥系统性能,提供了合理完备的实用性数值模拟工具．     

二维撒施畦灌地表水流溶质运移模型:Ⅱ验证

基于撒施施肥方式下畦灌试验数据,从传统平均相对误差和马尔科夫随机过程两个角度,对二维撒施畦灌地表水流溶质运移模型进行了验证．基于传统平均相对误差的结果表明,模型模拟的水流推进与消退的平均相对误差分别为498％和937％,水量平衡误差为028％,模拟各测点的溶质质量浓度变化过程平均相对误差为864%～1422％,溶质平衡误差058％,构建的模型不仅具有较好的模拟二维撒施畦灌地表水流运动和溶质质量浓度变化过程的能力,还具备较佳的水量与溶质质量守恒性．基于马尔科夫随机过程的计算结果表明,地形项的随机性对模拟效果的影响为8868％～9621％,而畦面土壤物理属性等模型未能考虑因素的随机性对各测点溶质质量浓度变化的影响为379％～1132％,因此仅考虑畦面微地形分布随机性的模型,具备优良的二维撒施畦灌地表水流和溶质运移过程的模拟性能．构建的模型为评价撒施施肥方式下的畦灌施肥系统性能,提供了合理完备的实用性数值模拟工具．     

Empirical functions for dependent variables in cutback furrow irrigation

Water scarcity and the high consumption of water resources in agriculture have strengthened the need to manage and optimize irrigation systems. Among surface irrigation systems, furrow irrigation with cutback is commonly used because of its potentially higher irrigation efficiency, lower costs and relative simplicity. The performance of this system is affected by various management and design variables, and hence different management scenarios should be evaluated before it is applied in practice. For this purpose, empirical functions for the performance evaluation indices are useful. This paper employs sensitivity, dimensional and regression analyses in the development of empirical functions for application efficiency, deep percolation, runoff and distribution uniformity. The proposed functions were evaluated using a numerical zero-inertia model and field measured data. Coefficients of determination for E _a, D _r, R _r and U _cc were calculated to be 0.90, 0.91, 0.90 and 0.84, respectively. These values indicate that the proposed functions enable the performance indices to be predicted satisfactorily. Values for the indices calculated using the developed dimensionless functions showed a very good agreement with both the outputs of the zero-inertia model and values calculated from measured field data. As the functions were general (not site and irrigation specific) and explicit, they could prove to be of practical significance in both conventional and optimal design and management of free-draining, graded furrow irrigation systems with cutback flows.

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Stochastic modeling of basins microtopography: analysis of spatial variability and model testing

Microtopography is among the most important factors affecting the performance of basin irrigation system due to its influence on the advance and recession processes. This study is based on field-measured surface elevation of 116 basins in North China. The spatial variability of basins microtopography was analyzed using geostatistics; the spatial structure of basins microtopography can be characterized by a spherical semivariogram model. The correlations between selected basin geometry parameters, mainly the standard deviation (S _d ) of surface elevation differences (SED), and the semivariogram parameters were calculated and allow estimating the semivariogram parameters from basin characteristics. Considering the randomness of SED and, simultaneously, its spatial dependence, a procedure was developed to model the spatial distribution of SED using Monte-Carlo generation and kriging interpolation techniques. The required number of SED generations was also estimated depending upon the S _d of SED. The SED stochastic generation model was tested by comparing the advance, recession, flow water depths and performance parameters observed in an experimental basin with those simulated using measured and model generated SED data. Results show that estimation errors from using generated data are similar to those resulting from observations. Thus, SED generated data may be used for assessing the impacts of microtopography on irrigation performance.     

Empirical functions for dependent furrow irrigation variables.

A complete set of dependent furrow irrigation variables has been identified, for which empirical functions, of general applicability, have been developed. A one-dimensional sensitivity analysis technique coupled with dimensional analysis was employed to reduce the number of independent irrigation variables to a manageable size. Simulation experiments were carried out to generate the data used in developing the pertinent functional relationships. Regression analysis was used to ascertain the specific form of the equations. The predictive quality of the functions has been assessed by comparing their output with those of a zero-inertia model, and was found to be satisfactory. Received: 22 May 1996     

Modeling and error analysis of kinematic-wave equations of furrow irrigation

A moving control volume approach was used to model the advance phase of a furrow irrigation system whereas a fixed control volume was used to model the nearly stationary phase and the runoff rate. The resulting finite-difference equations of the kinematic-wave model were linearized and explicit algebraic expressions were obtained for computation of advance and runoff rate. The solutions for the advance increment and the runoff rate were compared with the nonlinear scheme, the zero-inertia model, and a set of field data. A close agreement was found between the models and the field data. Assuming a constant infiltration rate, a differential equation was derived to estimate the error between the kinematic-wave model and the zero-inertia model in predicting the flow cross-sectional area along the field length. The differential equation and two dimensionless terms were used to define the limits for use of the kinematic-wave model in furrow irrigation.     

基于非恒定渐变流-急变流方程的变流量畦灌数值模型

传统畦灌模型多是基于非恒定渐变流方程建立的,在模拟变流量畦灌水流运动时的精度难以保障。本文综合分析了变流量畦灌过程中田面水流的运动状况,将其按照边界条件的不同划分为恒定流量进水阶段、变流量进水阶段、畦首消退阶段、田面消退第1阶段、田面消退第2阶段等5个阶段,基于非恒定渐变流方程和非恒定急变流方程构建了适用于变流量畦灌系统的渐变流-急变流数值模型,通过2组恒定流量畦灌、4组变流量畦灌的田间试验以及2组文献资料中的畦灌试验数据对模型进行了验证。结果表明,渐变流-急变流畦灌模型模拟值与现场实测结果吻合较好,模拟推进时间决定系数R2均大于0.96、模拟消退时间R2大于0.90。与目前常用的WinSRFR模型相比,渐变流-急变流畦灌数值模型在模拟恒定流量畦灌方面具有相似的精度,且在模拟变流量畦灌方面精度更高。渐变流-急变流畦灌模型可以较精准地模拟变流量畦灌的水流运动状况,可为分析变流量畦灌系统、优化变流量畦灌方案提供支撑。