Infiltration parameters from optimisation on furrow irrigation advance data

Knowledge of the soil infiltration parameters is necessary for efficient furrow irrigation. A method is proposed for the determination of the parameters in the Kostiakov-Lewis infiltration equation from measurements of the furrow irrigation advance and inflow. The method employs a volume balance model using optimisation to minimise the error between the predicted and measured advance and differs from existing approaches in that only advance data and inflow rates are required. The average cross sectional area of the furrow and the final infiltration rate are treated as fitted parameters and need not be measured. A simple but effective optimisation algorithm is developed which allows for the solution of the four parameters without user input. The speed and simplicity of the optimisation may lead to application in real-time control of furrow irrigation. Received: 16 August 1995     

Estimating the furrow infiltration characteristic from a single advance point

Management and control of surface irrigation, in particular furrow irrigation, is limited by spatio-temporal soil infiltration variability as well as the high cost and time associated with collecting intensive field data for estimation of the infiltration characteristics. Recent work has proposed scaling the commonly used infiltration function by using a model infiltration curve and a single advance point for every other furrow in an irrigation event. Scaling factors were calculated for a series of furrows at two sites and at four points down the length of the field (0.25 L, 0.5 L, 0.75 L and L). Differences in the value of the scaling factor with distance were found to be a function of the shape of the advance curves. It is concluded that use of points early in the advance results in a substantial loss of accuracy and should be avoided. The scaling factor was also strongly correlated with the furrow-wetted perimeter suggesting that the scaling is an appropriate way of both predicting and accommodating the effect of the hydraulic variability.     

The comparison of advance and erosion of meandering furrow irrigation with standard furrow irrigation under varying furrow inflow rates

Meandering furrow irrigation (Gholam-gardeshi irrigation) is a modified form of furrow irrigation, which has being used in Iran, but to date, there is no study about the erosion of this method of irrigation. To measure the erosion of meandering furrow irrigation and to compare the results with standard furrow irrigation, two experimental fields with different soil textures and furrow inflow rates were used. The experiment utilized a randomized factorial design with three replications for each treatment. In both methods, the developed second order polynomial equation for the erosion, and advance equation were able to predict the field data with coefficients of determination of more than 0.94. The results showed that the velocity of advance, tail water runoff and erosion are significantly lower for meandering furrow irrigation as compared to standard furrow irrigation. As the furrow inflow rates increased, erosion and runoff in both irrigation methods increased significantly.     

土壤入渗特性和田面糙率的变异性对沟灌性能的影响

以杨凌区粘壤土和砂壤土区域进行的大田沟灌试验为基础,在假定各灌水沟内部土壤入渗特性和糙率均一的条件下,重点分析各灌水沟之间土壤入渗参数和田面糙率的不同组合对沟灌水流运动过程和灌水质量的影响,结果表明土壤入渗特性的变异性对沟灌水流推进过程和灌水质量指标影响较大,在模拟时必须充分考虑;而田面糙率的变异性对沟灌水流推进过程和灌水质量指标影响较小,可采用田块糙率均值代替各灌水沟的糙率。经实例验证,水流推进过程相对误差为7.28%,灌水效率、灌水均匀度和储水效率模拟值与实测值误差分别为5.74%、6.18%和4.07%,结果表明其模拟效果较好。     

Furrow infiltration estimation from time to a single advance point

A simple and quick method to determine the Soil Conservation Service (SCS) intake function in furrow irrigation is presented. The time of advance at only one location of the field, inflow rate, and average flow area are the only field data required to estimate the two parameters of the SCS infiltration equation. The dependence of the two intake parameters, k and α, of the SCS intake function was expressed analytically and then the single unknown intake parameter of the SCS function, α, could be determined by applying a volume–balance (VB) equation using a power advance assumption. Estimates of infiltration by the proposed method were compared with measured furrow infiltration data and a recently developed one-point method which uses the two parameter Philip infiltration equation, but is restricted by an assumption that the advance trajectory follows the power function with the exponent of 1/2. It is shown that the proposed one-point method can give more accurate results than the previous one-point method.     

A real-time optimisation system for automation of furrow irrigation

An automated real-time optimisation system for furrow irrigation was developed and tested in this study. The system estimates the soil infiltration characteristics in real time and utilises the data to control the same irrigation event to give optimum performance for the current soil conditions. The main components of the system are as follows: the sensing of flow rate and a single advance time to a point approximately midway down the field, a system for scaling the soil infiltration characteristic and a hydraulic simulation program based on the full hydrodynamic model. A modem is attached to a microcomputer enabling it to receive signals from the flow meter and advance sensor via a radio telemetry system. Sample data from a furrow-irrigated commercial cotton property are used to demonstrate how the system works. The results demonstrate that improvements in on-farm water use efficiency and labour savings are potentially achievable through the use of the system.     

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.     

Development of an adaptive surface irrigation system

Cablegation is a simple system for automating surface irrigation in small- and medium-sized fields using a gated pipe. In this work, a Programmable Logic Control, PLC, was used to develop an adaptive cablegation system capable of establishing the infiltration equation in real time and then adjusting the irrigation times to the infiltration rate and field geometry. A controlling program was developed for the on-field determination of the infiltration equation, simulation of advance in each furrow, and the optimization and management of the irrigation event. The equipment was tested in three experimental stations, including a Luvissol field organized in contour terraces with furrows of various lengths. The results demonstrate the capability of the system to adapt the application times to the different furrow lengths and the gradual decrease in the soil infiltration and to recommend an application depth that optimizes the Application Efficiency. Various improvements were made to this solar-powered cablegation, resulting in a reliable surface irrigation system capable of unsupervised operation.     

沟灌交汇入渗数学模型研究

为进一步探明沟灌灌水沟的水分入渗规律,通过室内沟灌入渗试验,分析了沟灌交汇入渗的入渗规律,建立了沟灌交汇入渗的二阶段入渗模型,研究了沟灌交汇入渗相对与沟灌自由入渗的减渗特性。在此基础上建立了计算沟灌交汇起始时间的计算模型,得出了沟灌交汇入渗阶段的累积减渗量与入渗时间呈幂函数关系,并建立了沟灌交汇入渗减渗率η的公式,将其计算结果和沟灌自由入渗的累积入渗量用文中公式计算,可求得沟灌交汇入渗阶段的累积入渗量,与试验所得结果进行比较,其误差较小,表明建立的减渗率η的计算公式是可靠的。研究结果可为改进沟灌灌水技术提供参考。     

Simulation of furrow irrigation practices (SOFIP): a field-scale modelling of water management and crop yield for furrow irrigation

Because of the spatial and temporal variabilities of the advance infiltration process, furrow irrigation investigations should not be limited to a single furrow irrigation event when using a modelling approach. The paper deals with the development and application of simulation of furrow irrigation practices (SOFIP), a model used to analyse furrow irrigation practices that take into account spatial and temporal variabilities of the advance infiltration process. SOFIP can be used to compare alternative furrow irrigation management strategies and find options that mitigate local deep-percolation risks while ensuring a crop yield level that is acceptable to the farmer. The model is comprised of three distinct modelling elements. The first element is RAIEOPT, a hydraulic model that predicts the advance infiltration process. Infiltration prediction in RAIEOPT depends on a soil moisture deficit parameter. PILOTE, a crop model, which is designed to simulate soil water balance and predict yield values, updates the soil moisture parameter. This parameter is an input of a parameter generator (PG), the third model component, which in turn provides RAIEOPT with the data required to simulate irrigation at the scale of an N-furrow set. The study of sources of variability and their impact on irrigation advance, based on field observations, allowed us to build a robust PG. Model applications show that irrigation practices must account for inter-furrow advance variability when optimising furrow irrigation systems. The impact of advance variability on deep percolation and crop yield losses depends on both climatic conditions and irrigation practices.     

Application of the optimization method for estimating infiltration characteristics in furrow irrigation and its comparison with other methods

The infiltration characteristics of a soil vary spatially and temporally, and due to this the available methods for estimating the characteristics in furrow irrigation are either not suitable or have restrictions for their field use. An optimization method based on the volume balance approach, originally developed for estimating infiltration parameters in border irrigation, and using multiple observations of arrival time of the wetting front was modified for furrow irrigation. The method was applied to 13 irrigation events on furrows monitored on a farm in northern New South Wales, Australia. The soil type at the experimental site has a high clay content (up to 67%) and develops cracks when dry. In addition to the optimization method, one-point and two-point methods using observations of arrival time reported in the literature were also used. The accuracy of different methods was evaluated by comparing the calculated total volume of water infiltrated into the furrow with that observed in the field. The optimization method was the most accurate and the one-point and the two-point were the least accurate among three methods considered in the present study. A possible explanation for a poor performance of the one-point and two-point methods might be related to the assumptions made in the derivation of the methods and the unsuitability of the Philip and the Kostiakov infiltration equations used for the field condition in the present study.     

Estimation of advance and infiltration equations in furrow irrigation for untested discharges

The exponents of the advance and infiltration power laws have been shown to remain practically constant for different furrow irrigation discharges. Under this hypothesis, a procedure to estimate the advance and infiltration equations corresponding to untested discharges was developed. The proposed procedure was validated with different field experiments, obtaining satisfactory results for non-erosive discharges. However, significant deviations were obtained when erosive discharges were used. This behavior corroborates the hypothesis presented by some authors that the erosion and sedimentation processes occurring in furrow irrigation as a consequence of high surface velocities can reduce—and even suppress—the effect of the wetted perimeter on the infiltration rate. Finally, an equation was derived to predict the effect of the wetted perimeter on the infiltration parameters.     

Field values of the shape factor for estimating surface storage in furrows on a clay soil

Surface storage of water in furrow irrigation is an important parameter in volume balance analysis for computing different parameters such as infiltration characteristics. Surface storage can be estimated in several ways. A commonly used method is to multiply the cross-sectional area of flow at the inlet of a furrow by a shape factor, whose value is often assumed to vary between 0.7 and 0.8. In this study, field data for 13 furrow irrigation events were collected from a farm in northern New South Wales, Australia. These data were used to investigate the validity of the assumption regarding the value of the shape factor. The soil type at the experimental site has a high clay content (up to 67%) and develops cracks when dry. The values of the shape factor calculated for the irrigation events in the study varied from 0.96 to 1.8, and varied between furrows and from one irrigation to the next in the same furrow. They also varied considerably during a given irrigation event. It is therefore incorrect to assume a constant value of the shape factor between 0.7 and 0.8 in mathematical models of furrow irrigation. Received: 6 May 1996     

Prediction of surface irrigation advance using soil intake properties

A simple method for predicting surface irrigation advance trajectories using infiltration parameters and inflow rate as inputs was developed. The difference between the inflow rate and the sum of infiltration rates over the wetted portion of the field equals the flow rate available for advance. An average (characteristic) infiltration rate ahead of the wet portion is computed using a fixed time step. An advance step (for a fixed time step) is calculated from the ratio of the flow rate available for advance and characteristic infiltration rate. Predictions of advance by the proposed method were compared with field observations, with the kinematic wave model, and with analytical solutions of Philip and Farrell (1964). In all cases, the method provided predictions that were in good agreement with field observations, and performed similarly to the kinematic wave model. The method offers a simple and efficient tool for prediction and evaluation of surface irrigation systems under various soil types and variable inflow rates. The method is particularly useful for predictions in fields with spatially and temporally variable intake properties.     

保护地蔬菜栽培不同灌水方法对表层土壤盐分含量的影响

通过 3年连续保护地栽培蔬菜小区试验 ,对滴灌、渗灌、沟灌 3种灌水方法的土壤盐分积累状况进行了比较研究。试验后 0～ 2 0 cm土层土壤全盐含量以沟灌最高 ,渗灌次之 ,滴灌最低 ;滴灌土壤 p H下降幅度明显低于渗灌和沟灌土壤。在 0～ 2 0 cm土层内全盐含量呈幂指数形式分布 ,即地表处含量最高 ,随深度增加逐渐下降 ;而土壤 p H则随深度增加而直线上升。另外 ,土壤中可溶性盐的阴离以 NO-3 为主 ,阳离子以 Ca2 + 为主。这说明选择合理灌水方法 ,是防止土壤退化、提高保护地作物产量和质量的有效途径。     

应用水量平衡法确定波涌灌溉下土壤入渗参数

基于田间实测的地表水流推进过程 ,利用水量平衡法推求波涌灌溉间歇供水条件下的土壤入渗参数。在此基础上 ,利用地面灌溉模型模拟田间水流推进过程并与实测值作对比后发现 ,与单点入渗测试方法相比较 ,该法不仅具有较高的参数估值精度 ,还具备田间试验工作量相对较小、应用简便等特点 ,具有较好的实用价值。     

Evaluation of time domain reflectometry (TDR) for estimating furrow infiltration

TDR was used to estimate furrow infiltration, which is a key component in furrow irrigation system design and management. Furrow irrigation experiments were conducted on bare and cropped fields consisting of three 40 m long parabolic shaped furrows spaced at 0.8 m on a slope of 0.5%. The centre furrow was taken as the study furrow and the other two provided a buffer to the centre furrow. Altogether, 22 irrigations were conducted during 2004 and 2005 with inflow rates ranging from 0.1 to 0.7 l s⁻¹. TDR probes were installed vertically around the centre furrow at four locations 0.5 (S₁), 13 (S₂), 26 (S₃) and 39.5 m (S₄) from the inlet end. The S₁ and S₃ locations had four TDR probes installed at 0.15, 0.30, 0.45 and 0.60 m depths whereas the S₂ and S₄ locations had two probes each at 0.15 and 0.30 m depths. Soil moisture data collected at 5-min intervals were used to determine the average soil moisture content of the field. The change in moisture content was used to estimate the furrow infiltration which was compared with that measured using an inflow–outflow (IO) method. The performance of the TDR method was studied by calculating the absolute prediction error (APE), root mean square error (RMSE) and index of agreement (I _a). It was found that the TDR-method estimated furrow infiltration well for higher inflow rates and during the initial stages of irrigation. APE decreased and I _a increased with increase in flow rate for both bare and cropped conditions. The APE and RMSE were found to be larger for a cropped field than the bare field when irrigated at the same inflow rate. The accuracy of the TDR-method for estimating total infiltration was improved by using the average field moisture content of 30 or 45 min after the recession phase ceased. These results indicate that TDR can be used to estimate in situ infiltration under furrow irrigation.     

沟灌条件下灌水沟入渗特性研究

为探明沟灌时灌水沟的水分入渗规律,从沟灌二维入渗过程、入渗湿润锋运移特性、累计入渗水量变化过程、土壤含水量分布等方面研究了沟灌的入渗特征及其影响,研究表明：灌水沟中水深、沟底宽、湿周对沟灌入渗过程均有明显影响。沟中水深增大,有利于加大侧向入渗,垂向入渗减少,而水深减小,会加大垂向入渗,增加深层渗漏。灌水沟底宽不影响灌水沟的侧向入渗,仅影响垂向入渗,底宽减小,垂向入渗深度相应减小,且土壤表面以下40 cm深以内水平向入渗深度平均值与最大垂向入渗深度的比值在沟底宽小时均大于沟底宽大时。合理的断面形式和大小有利于减小垂向入渗,加大水平侧向入渗,灌水沟断面形式为梯形断面时,宽深比近似为2效果最优。研究结果可为改进沟灌灌水技术提供参考。     

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.     

Evaluation of various quick methods for estimating furrow and border infiltration parameters

For estimating infiltration properties of surface irrigation, some ‘quick’ and easy methods have been developed. The main objective of this study was to evaluate different ‘quick’ methods and to compare the obtained results with two new methods proposed based on the Shepard one-point approach. For this purpose, data sets measured in six borders and five furrows were used for evaluating different methods. Using the volume balance equation and estimated infiltration parameters, the total infiltrated volume and advance times were predicted to evaluate the accuracy of estimated infiltration parameters. The results showed that the modified Mailapalli and Elliott and Walker methods provided the lowest errors for both furrow and border irrigations. The Elliott and Walker method predicted advance times with highest accuracy. There was very small difference between the Shepard and new proposed one-point methods. The performance of the Elliott and Walker method was slightly better than the new proposed two-point method for the experimental furrows, while a minor difference was found for the experimental borders. The results also showed that the performance of the Elliot and Walker method would be improved using binomial approximation instead of Kiefer approximation.