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1.
Koichi Unami Macarius Yangyuoru Abul Hasan Md. Badiul Alam Gordana Kranjac-Berisavljevic 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):77-89
Micro-dams are expected to be feasible options for water resources development in semi-arid regions such as the Guinea savanna agro-ecological zone of West Africa. An optimal water management strategy in a micro-dam irrigation scheme supplying water from an existing reservoir to a potential command area is discussed in this paper based on the framework of stochastic control. Water intake facilities are assumed to consist of photovoltaic pumping system units and hoses. The knowledge of current states of the storage volume of the reservoir and the soil moisture in the command area is fed-back to the intake flow rate. A system of two stochastic differential equations is proposed as a model for the dynamics of the micro-dam irrigation scheme, so that temporally backward solution of the Hamilton–Jacobi–Bellman equation determines an optimal control, which represents the optimal water management strategy. A computational procedure using the finite element method is successfully implemented to provide comprehensive information on the optimal control. The results indicate that the water initially stored in the reservoir can support full irrigation for about 80 days under the optimal water management strategy, which is predominantly based on the demand-side principle. However, the volatility of the soil moisture in the command area must be reasonably small. 相似文献
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Verifying optimality of rainfed agriculture using a stochastic model for drought occurrence 总被引：1，自引：1，他引：0
Erfaneh Sharifi Koichi Unami Macarius Yangyuoru Masayuki Fujihara 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(5):1503-1514
It may be paradoxical but subsistence rainfed agriculture is the predominant source of food in Sub-Saharan Africa where the production uncertainty is associated with the stochastic nature of rainfall. This paper attempts to comprehend the rationale of this situation by a mathematical approach. Considering the level of drought severity as the zero-reverting Ornstein–Uhlenbeck process, optimality of rainfed agriculture is investigated in the context of stochastic control theory. Occurrence of drought terminating growth of crops is modelled with the concept of first exit time. A stochastic control problem allowing for virtual cost of irrigation, water stress to crops, and benefits of farming is formulated with irrigation effort as the control variable. The Hamilton–Jacobi–Bellman equation governing the optimal control is studied to identify the set of cost functions optimizing rainfed agriculture in an inverse problem approach. Data and information were collected in the coastal savanna agro-ecological zone of Ghana, to identify model parameters, formulate the stochastic control problem, solve the inverse problem, and then verify optimality of rainfed agriculture. The results indicated that rainfed agriculture is not optimal when the crop is more tolerant to water stress. 相似文献
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A. C. LIAKOPOULOS Dr. Eng. 《水文科学杂志》2013,58(1):69-110
ABSTRACT The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content. Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data. Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme. Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate. 相似文献
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数值差分格式及格点设置对土壤温度模拟结果的影响 总被引：2，自引：2，他引：0
土壤温度是反映气候系统和生态系统能量循环的重要地球物理学参量,土壤温度的模拟精度直接影响着气候系统模式以及陆面物理过程模式的模拟结果.为了提高模式对土壤温度的模拟能力,本文利用土壤热扩散方程的傅里叶解析解定量研究了差分方案、格点设置以及时间步长对土壤温度模拟结果的影响;提出了一种优化的格点设置方案,并利用巴丹吉林沙漠观测数据检验了该方案的性能.研究结果表明:三种差分方案中,显式方案的模拟误差最小,Crank-Nicolson方案其次,隐式方案的模拟误差最大;每一种格点设置方案均存在一个使模拟结果误差最小的最优化时间步长;常用格点设置方案的最优化时间步长为5358 s,最小标准差为0.156 K,优化方案的最优化时间步长为1694 s,最小标准差为0.0465 K;取时间步长为1800 s时,采用常用格点设置方案,巴丹吉林沙漠10 cm深度土壤温度模拟结果的标准差为1.61 K,而采用优化方案,模拟结果的标准差降至0.21 K,改进效果明显. 相似文献
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MAHDI S. HANTUSH 《水文科学杂志》2013,58(2):40-60
Abstract Fresh-water lenses are formed in unconfined saline aquifers in response to deep percolation from rainfall, artificial recharge, and seepage from irrigation waters and/or in response to injecting fresh water through vertical or horizontal wells. An approximate differential equation is derived in terms of the depth of the fresh-salt water interface below the initial position of the saline-water table. This equation is analogous to that of the ground-water motion in two dimensions. The wealth of knowledge available from solving the latter equation is used to obtain approximate expressions for the movement of the fresh-salt water interface in several flow systems wherein this interface does not reach the bottom of the aquifer. These approximate solutions as well as others for related quantities of interest may afford useful tools for rationally planning the extraction of usable waters from such flow systems. 相似文献
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Simulated impacts of irrigation on evapotranspiration in a strongly exploited region: a case study of the Haihe River basin,China 
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下载免费PDF全文 Irrigation is the major water supply for crop production in water‐limited regions. However, this important water component is usually neglected or simplified in hydrological modelling primarily because information concerning irrigation is notably difficult to collect. To assess real effects of irrigation on the simulation of evapotranspiration (ET) in water‐limited region, the Community Land Model version 4 was established over a typical semi‐humid agricultural basin in the northern China – the Haihe River basin. In the irrigated cropland, incorporating an irrigation scheme can enhance the simulated ET and improve the simulation of spatial variability of soil moisture content. We found that different configurations in the irrigation scheme do not cause significant differences in the simulated annual ET. However, simulated ET with simulated irrigation differs clearly from that with observed irrigation in mean annual magnitude, long‐term trend and spatial distribution. Once the irrigation scheme is well‐calibrated against observations, it reasonably reproduces the interannual variability of annual irrigation, when irrigation water management is relatively stable. More importantly, parameter calibration should be consistent with the configuration of the source of irrigation water. However, an irrigation scheme with a constant parameter value cannot capture the trend in the annual irrigation amount caused by abrupt changes in agricultural water management. Compared with different remotely sensed ET products, the enhancement in the simulated ET by irrigation is smaller than the differences among these products, and the trend in simulated ET with the observed irrigation cannot be captured correctly by the remotely sensed ET. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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笛卡尔坐标系中的经典程函方程在静校正、叠前偏移、走时反演、地震定位、层析成像等很多地球物理工作中都有应用,然而用其计算起伏地表的地震波走时却比较困难.本文通过把曲线坐标系中的矩形网格映射到笛卡尔坐标系的贴体网格,推导出曲线坐标中的程函方程,而后,用Lax-Friedrichs快速扫描算法求解曲线坐标系的程函方程.研究表明本文方法能有效处理地表起伏的情况,得到准确稳定的计算结果.由于地表起伏,导致与之拟合的贴体网格在空间上的展布呈各向异性,且这种各向异性的强弱对坐标变换法求解地震初至波的走时具有重要影响.本文研究表明,随着贴体网格的各向异性增强,用坐标变换法求解地表起伏区域的走时计算误差增大,且计算效率降低,这在实际应用具有指导意义. 相似文献
9.
Jing‐Bo Chen 《Geophysical Prospecting》2014,62(2):258-277
Based on an average‐derivative method and optimization techniques, a 27‐point scheme for a 3D frequency‐domain scalar wave equation is developed. Compared to the rotated‐coordinate approach, the average‐derivative optimal method is not only concise but also applies to equal and unequal directional sampling intervals. The resulting 27‐point scheme uses a 27‐point operator to approximate spatial derivatives and the mass acceleration term. The coefficients are determined by minimizing phase velocity dispersion errors and the resultant optimal coefficients depend on ratios of directional sampling intervals. Compared to the classical 7‐point scheme, the number of grid points per shortest wavelength is reduced from approximately 13 to approximately 4 by this 27‐point optimal scheme for equal directional sampling intervals and unequal directional sampling intervals as well. Two numerical examples are presented to demonstrate the theoretical analysis. The average‐derivative algorithm is also extended to a 3D frequency‐domain viscous scalar wave equation. 相似文献
10.
《Advances in water resources》2005,28(8):793-806
In this paper, the numerical errors associated with the finite difference solutions of two-dimensional advection–dispersion equation with linear sorption are obtained from a Taylor analysis and are removed from numerical solution. The error expressions are based on a general form of the corresponding difference equation. The variation of these numerical truncation errors is presented as a function of Peclet and Courant numbers in X and Y direction, a Sink/Source dimensionless number and new form of Peclet and Courant numbers in X–Y plane. It is shown that the Crank–Nicolson method is the most accurate scheme based on the truncation error analysis. The effects of these truncation errors on the numerical solution of a two-dimensional advection–dispersion equation with a first-order reaction or degradation are demonstrated by comparison with an analytical solution for predicting contaminant plume distribution in uniform flow field. Considering computational efficiency, an alternating direction implicit method is used for the numerical solution of governing equation. The results show that removing these errors improves numerical result and reduces differences between numerical and analytical solution. 相似文献
11.
《Advances in water resources》2003,26(6):635-647
A kinetic flux vector splitting (KFVS) scheme for shallow water flows based on the collisionless Boltzmann equation is formulated and applied. The scheme is explicit and first order in space and time with stability governed by the Courant condition. The consistency of the KFVS scheme with the shallow water equations is proven using the equivalent differential equations approach. The accuracy and efficiency of the KFVS scheme in modeling complex flow features are compared to those of the Boltzmann Bhatnagar–Gross–Krook (BGK) scheme as well as a Riemann-based scheme. In particular, all schemes are applied to (i) strong shock waves, (ii) extreme expansion waves, (iii) a combination of strong shock waves and extreme expansion waves, and (iv) a one-dimensional dam break problem. Additionally, the KFVS, BGK and Riemann schemes are applied to a one-dimensional dam break problem for which laboratory data is available. These test cases reveal that all three schemes provide solutions of comparable accuracy, but the KFVS model is 1.5–2 times faster to execute than the BGK scheme and 2–3 times faster than the Riemann-based scheme. The absence of the collision term from the Boltzmann equation not only makes the mathematical formulation of KFVS easy but also helps elucidate this approach to the novice. The accuracy, efficiency, and simplicity of the KFVS scheme indicate its potential in modeling an array of water resources problems. Due to the scalar nature of the Boltzmann equation, the extension of the KFVS scheme to 2-D surface water flows is straightforward. 相似文献
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Considerable effort has been devoted to develop optimal control methods for reducing structural response under seismic forces. In this study analytical solution of the linear regulator problem applied widely to the control of earthquake‐excited structures is obtained by using the sufficient conditions of optimality even though almost all of the optimal controls proposed previously for structural control are based on the necessary conditions of optimality. Since the resulting optimal closed–open‐loop control cannot be implemented for civil structures exposed to earthquake forces, the solution of the optimal closed–open‐loop control is carried out approximately based on the prediction of the seismic acceleration values in the near future. Upon obtaining the relation between the exact optimal solution and future values of seismic accelerations, it is shown numerically that the solution of the optimal closed–open‐loop control problem can be performed approximately by using only the first few predicted seismic acceleration values if a given norm criteria is satisfied. Calculated performance measures indicate that the suggested approximate solution is better than the closed‐loop control and as we predict the future values of the excitation more accurately, it will approach the optimal solution. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
14.
基于模拟优化与正交试验的库塘联合灌溉系统水资源调控 总被引：1，自引：1，他引：0
依托灌溉试验站田间降水-作物耗水-土壤水相互转化的长序列试验成果,构建灌区田间尺度水量蓄-耗-灌-排全过程的水资源模拟模块,结合系统仿真方法,建立库塘联合灌溉系统水量分配仿真模拟模型,以保障灌区基本需水(包括农村生活需水与生态环境需水)供水安全前提下的经济效益最大化为目标,运用正交试验选优原理,构建了库塘联合灌溉系统水资源优化调控模型,形成了基于仿真模拟与正交试验优化的库塘联合灌溉系统水资源优化调控技术体系,并应用于巢湖流域大官塘水库灌区,明确了灌区合理的工程布局规格与规模,确定了适宜的节水灌溉技术模式与灌溉制度,制定了塘坝和水库科学的调度规则,提出了具有可操作性的作物种植结构调整规则,提高了灌区径流拦蓄利用率,提升了塘坝和水库年际调蓄供水能力,增强了抗旱减灾能力,为巢湖流域水库灌区综合治理、库塘联合灌区水量分配方案、水库和塘坝调度规则及作物灌溉制度等地制定提供理论依据. 相似文献
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The analysis of infiltration of 2D trickle irrigation under multiple‐line sources, governed by the celebrated Richards equation, is performed, aiming at determining the efficiency of trickle irrigation so as to reduce the water demand. A closed‐form solution is explicitly obtained by utilizing the Fourier integral transformation, and this serves as a means to compute the distribution of volumetric water content during trickle irrigation. Results for the infiltration of 2D trickle irrigation under single line and multiple‐line sources are presented, which illustrate the distribution of infiltration water that diffuses into the soil, and make it possible to calculate the period of time required for trickle irrigation for different plants. The results can be applied to verify complicated solutions from other numerical models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Assessing crop yield and crop water productivity and optimizing irrigation scheduling of winter wheat and summer maize in the Haihe plain using SWAT model 下载免费PDF全文
下载免费PDF全文 Haihe plain is an important food production area in China, facing an increasing water shortage. The water used for agriculture accounts for about 70% of total water resources. Thus, it is critical to optimize the irrigation scheduling for saving water and increasing crop water productivity (CWP). This study first simulated crop yield and CWP for winter wheat and summer maize in historical scenario during 1961–2005 for Haihe plain using previously well‐established Soil and Water Assessment Tool model. Then, scenarios under historical irrigation (scenario 1) and sufficient irrigation (scenario 2) were, respectively, simulated both with sufficient fertilizer. The crop yield in scenario 2 was considered as the potential crop yield. The optimal irrigation scheduling with sufficient fertilizer (scenario 3) was explored by iteratively adjusting irrigation scheduling based on the scenario 1 and previous studies related to water stress on crop growth. Results showed that net irrigation amount was, respectively, reduced 23.1% and 18.8% in scenario 3 for winter wheat and summer maize when compared with scenario 1. The CWP was 12.1% and 8.2% higher with very slight change of crop yield. Using optimal irrigation scheduling could save 8.8 × 108 m3 irrigation water and reduce about 16.3% groundwater over‐exploitation in winter wheat growth period. The corresponding yield was 18.5% and 12.9% less than potential yield for winter wheat and summer maize but using less irrigation water. Therefore, it could be considered that the optimal irrigation was reasonable, which provided beneficial suggestions for increasing efficiency of agricultural water use with sustainable crop yield in Haihe plain. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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As an alternative approach to classical turbulence modelling using a first or second order closure, the data assimilation method of optimal control is applied to estimate a time and space-dependent turbulent viscosity in a three-dimensional oceanic circulation model. The optimal control method, described for a 3-D primitive equation model, involves the minimization of a cost function that quantifies the discrepancies between the simulations and the observations. An iterative algorithm is obtained via the adjoint model resolution. In a first experiment, a k ± L model is used to simulate the one-dimensional development of inertial oscillations resulting from a wind stress at the sea surface and with the presence of a halocline. These results are used as synthetic observations to be assimilated. The turbulent viscosity is then recovered without the k + L closure, even with sparse and noisy observations. The problems of controllability and of the dimensions of the control are then discussed. A second experiment consists of a two-dimensional schematic simulation. A 2-D turbulent viscosity field is estimated from data on the initial and final states of a coastal upwelling event. 相似文献
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Smallholder irrigation schemes are largely supply driven such that they exclude the beneficiaries on the management decisions and the choice of the irrigation schemes that would best suit their local needs. It is against this background that the decentralisation framework and the Dublin Principles on Integrated Water Resource Management (IWRM) emphasise the need for a participatory approach to water management. The Zimbabwean government has gone a step further in decentralising the management of irrigation schemes, that is promoting farmer managed irrigation schemes so as to ensure effective management of scarce community based land and water resources. The study set to investigate the way in which the Guyu-Chelesa irrigation scheme is managed with specific emphasis on the role of the Irrigation Management Committee (IMC), the level of accountability and the powers devolved to the IMC. Merrey’s 2008 critique of IWRM also informs this study which views irrigation as going beyond infrastructure by looking at how institutions and decision making processes play out at various levels including at the irrigation scheme level. The study was positioned on the hypothesis that ‘decentralised or autonomous irrigation management enhances the sustainability and effectiveness of irrigation schemes’. To validate or falsify the stated hypothesis, data was gathered using desk research in the form of reviewing articles, documents from within the scheme and field research in the form of questionnaire surveys, key informant interviews and field observation. The Statistical Package for Social Sciences was used to analyse data quantitatively, whilst content analysis was utilised to analyse qualitative data whereby data was analysed thematically. Comparative analysis was carried out as Guyu-Chelesa irrigation scheme was compared with other smallholder irrigation scheme’s experiences within Zimbabwe and the Sub Saharan African region at large. The findings were that whilst the scheme is a model of a decentralised entity whose importance lies at improving food security and employment creation within the community, it falls short in representing a downwardly accountable decentralised irrigation scheme. The scheme is faced with various challenges which include its operation which is below capacity utilisation, absence of specialised technical human personnel to address infrastructural breakdowns, uneven distribution of water pressure, incapacitated Irrigation Management Committee (IMC), absence of a locally legitimate constitution, compromised beneficiary participation and unclear lines of communication between various institutions involved in water management. Understanding decentralization is important since one of the key tenets of IWRM is stakeholder participation which the decentralization framework interrogates. 相似文献
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《Journal of Hydrology》1999,214(1-4):8-17
Understanding the influence of irrigation methods on solute transport is essential to properly manage chemical use in agricultural soils. In this study, we compare the transport of a conservative solute (bromide) under sprinkler and flood irrigations on a sandy clay loam (mixed Ustollic Haplargid) under no-till condition. After spraying 148.8 kg/ha of KBr on the surface, ≈25 cm of irrigation water was applied in six increments over two months as flood irrigation on one plot and as sprinkler irrigation on another plot. The net applied water (NAW=irrigation+precipitation−evaporation) was similar for both plots, which allowed the comparison of the Br profiles for the two types of irrigation. Water content and Br concentration were sampled at 5, 19, 34, and 68 days after chemical application.The recovered mass of Br and the location of center of mass were comparable for the two types of irrigation. The spread around the center of mass, however, was higher for the flood-irrigated plot. On the flood-irrigated plot, more mass leached below the depth of 90 cm, with the differences being statistically significant. The velocity of the Br center of mass was consistently 10%–20% larger than the piston displacement velocity. Dispersion and velocity coefficients varied substantially between sampling time. A recent quasi-steady solution of the convection–dispersion equation [M.H. Nachabe, L.R. Ahuja, Quasi-analytical solution for predicting the redistribution of surface-applied chemicals. Trans. ASAE 39(5) (1996) 1659–1664], which accounts for variable flow and dispersion, simulates the Br profiles fairly well. 相似文献
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《Advances in water resources》1998,22(1):1-16
A model for transport of solutes in a porous medium participating in a dissolution–precipitation reaction, in general not in equilibrium, is studied. Ignoring diffusion–dispersion the initial value problem for piecewise constant initial states is studied, which e.g. for ionic species include a change of the ionic composition of the solution. The mathematical solution, nearly explicitly found by the method of characteristics up to the (numerical) solution of an integral equation for the position of the dissolution front, exhibits a generalized expanding plateau-structure determined by the dissolution front and the water flow (or salinity) front. 相似文献