A method was developed for the design of microirrigation laterals based on the required average emitter discharge and the required uniformity of water application. The finite-element method was used to analyze the hydraulics of a lateral. The golden section search was employed to find the operating pressure head of the lateral that can produce the required average emitter discharge along the lateral, Analytical results show that the lateral length for the required uniformity of water application may have three solutions and the diameter may have two solutions when laterals are laid on sloped fields. The design procedure was implemented. When the required average emitter discharge, the required uniformity of water application, one parameter-either the lateral length or diameter, and other conditions are given, then the unknown parameter, the best submain position (paired laterals), and the operating pressure head can be accurately obtained using personal computers. A flowchart of the computer program for design of the length of paired laterals is included.
One of the basic assumptions of the hydrological volume balance models in surface irrigation implies that furrow inflow instantaneously increases to a constant rate: the step-flow condition. Unfortunately this assumption is not always met in the field. Inflow variation is mainly due to the operations required to switch from one set to another, even with an automated furrow irrigation system such as gated pipe. In that regard, siphons are less sensitive to the operations and may be generally considered as a step-how application system. Furthermore, the presence of a flume at the upstream end of the furrow can also perturb flow. The resulting gradual increase in flow reduces the stream advance rate at the beginning of the run. However, we demonstrate that later in the advance phase the velocity converges to the standard step-flow solution. Generally, advance-phase evaluation models incorrectly attribute the front slowdown to a very high infiltration rate. Two models were compared. The first, the Elliott and Walker model limited to the advance phase, identifies a Kostiakov-Lewis infiltration function with the constant term of infiltration set equal to zero. The second, the advance linear velocity (ALIVE) model, identifies a Horton function from the analysis of the advance rate. This study, based on analytical developments and on 72 furrow irrigation events, shows that the Elliott and Walker model is influenced by a non-step-inflow variation and underpredicts the infiltration amount. In contrast, the ALIVE model proposed by the writers is not as sensitive to the initial behavior of the flow, because it uses two-term rate functions for advance and infiltration.
Manually determining drainage patterns from topographical maps for a grid-based model is time consuming and occasionally subjective. Eight methods including neural network are developed in this study to automatically determine the pattern from Digital Elevation Model (DEM) data, These methods are tested for a subwatershed located on Chin-Mel Creek, Taipei County, Taiwan, R.O.C. Results obtained using the neural network method are superior to those obtained using the drainage network method, which has performed the best among the other seven methods excluding the neural network method. The neural network method has a self-learning capability that could likely replace human assessment involved in the conventional approach. The implementation of the drainage network and neural network methods is described. Performances of the two methods are compared on the basis of their differences from the manually determined result.
A nonsteady coupled aquifer solution is developed in which transient and steady-state drawdowns can be calculated in a pumped aquifer and in an overlying unpumped aquifer that is separated from the pumped aquifer by a semipermeable confining bed. The water pumped is from artesian storage in the pumped aquifer and leakage through the overlying confining bed. This leakage is from storage in the water-table aquifer and a reduction in evapotranspiration due to a decline in the water table. As a simplifying assumption, storage in the confining bed is neglected. This solution is different from existing analytical solutions in that steady-state conditions can be reached because a source term representing the evapotranspiration reduction is included in the differential equations that are solved. A Laplace-space solution obtained for the differential equations and boundary conditions is inverted to the time domain using the Stehfest numerical algorithm. The resulting time-dependent solution is an efficient tool for making preliminary estimates and identifying additional data needs. Also, it can be used to verify solutions obtained using more complex analytical and numerical models.
Knowledge of the sensitivity of performance and other related dependent furrow-irrigation parameters, in quantitative terms, to variations in field, design, and management variables can help save a considerable amount of cost, time, and effort spent in field data collection. A univariate analysis, based on the concept of relative sensitivity, was used to quantify the sensitivity of seven dependent irrigation parameters (E(a), E(r), R(r), D-r, U-cc, l(r), and t(a)) to 13 variables (t(co), S-0, sigma(1), sigma(2), rho(1), rho(2), n, k, a, c, l, q(0), and Z(r)). Three different data sets, representative of a wide range of irrigation, conditions have been used in the analysis. The response of each dependent parameter to variations in a variable has been evaluated using a zero-inertia model. It was found that no general conclusion can be drawn regarding the relative significance of variables in terms of their effect on each of the dependent parameters, since the interaction between variables is significant enough to weaken or strengthen the effect of changes in a given variable on a dependent parameter. Nevertheless, based on observed relative sensitivity clues, a qualitative categorization of variables into five sensitivity classes, with respect to each dependent parameter, was made.
The purpose of this study was to investigate the reliability of combining a surface irrigation model (SRFR) and two functional solute transport models (RAO and TETrans) in predicting the position of bromide (Br-) measured in a 0.81-ha field under furrow irrigation. The SRFR model was used to first predict the infiltrated depths and then RAO and TETrans models were used to predict the position of the solute. Solute was transported according to piston flow theory for the first irrigation and both models predicted the position of the solute with good accuracy. The solute was transported slightly faster than estimated by piston flow for the second irrigation, resulting in a reduction of correct predictions by both models. Both models predicted poorly for the third irrigation because deviations from piston flow were large. RAO model was more successful in predicting the peak solute position, while TETrans was more accurate in predicting mean solute depths. The latter was attributed to the differences between the two models and the sensitivity of TETrans to nodal spacing when predicting peak solute position.
The rational-method equation for estimating peak flow rates for storm-water runoff is derived from the balanced-design storm unit hydrograph approach presented in the U.S. Army Corps of Engineers HEC Training Document 15. The new form of the rational-method equation is Q(p) = (alpha I - phi)A, instead of the well known Q(p) = (I - phi)A; or Q(p) = alpha CIA, instead of the well known Q(p) = CIA, depending on the respective loss function used in the unit hydrograph effective rainfall model. The preceding fixed constant alpha is found to depend on the type of unit hydrograph used (i.e., S-Graph) and the log-log slope of the rainfall depth-duration curve, and is easily determined by equating to a known unit hydrograph design storm model peak flow rate result. This new development provides a significant foundation for the use of the well-known rational-method equation in small catchments where rainfall depth-area effects are negligible.
The quantile prediction acc;racy of the log-Pearson type III (LP3) distribution depends largely on the accuracy of the parameter-estimation method used. The performance of a parameter-estimation method, on the other hand, depends on both the individual population chosen from the LP3 family and the sample size. In this study Monte Carlo experiments were conducted to evaluate four parameter-estimation methods that are frequently used in hydrological analysis. The four methods tested are the method of indirect moments (MMI), the method of mixed moments (MIX), the method of direct moments (MMD), and a modification of MMI using optimization techniques (MMO). A quantile ratio index (QRI) was devised to identify the limits (sample size and LP3 population subset) within which each of these methods will perform best. This study suggests that when QRI less than or equal to 1.14, MMI or MMO should be used for sample size N less than or equal to 30, MIX for 30 < N < 100, and any of the four methods for N greater than or equal to 100. When QRI > 1.14, MMO is recommended for N less than or equal to 30, MIX for 30 < N < 100, and MIX, MMO, or MMI for N greater than or equal to 100. An application procedure was also developed and successfully applied to 10 randomly selected sites in Louisiana.
Simple calendars are described that express best dates of irrigation based on long-term weather data. The calendars are intended to promote easy and ready adaption of improved water management practices by farmers in both developed and developing countries by presenting simplified, nontechnical scheduling guidance. The calendars are developed using a daily soil-water balance-crop yield model. Once developed, the calendars require no updating and no further input by technical personnel. Calendars are developed for several planting dates, soil types and initial water contents. Developed calendars graphically show recommended irrigation occurrences expressed in days or weeks after sowing that correspond with the type of irrigation water delivery schedule utilized. The calendars are generalized as much as possible to promote widespread public usability. The graphical nature of the calendars encourages use by illiterate or semiliterate farmers. The methodology demonstrated is transferable to any site where sufficient weather data are available.
Procedures and guidelines are recommended for assessing integrity, quality, and reasonableness of measured weather data and equipment calibration for automated and electronic agricultural weather stations. The procedures include calculation of hourly and 24-h clear sky envelopes for solar radiation, validation of net radiation measurements using calculation equations, and evaluation of expected trends and relationships between air vapor content and air temperature. The procedures for creating clear sky solar radiation envelopes include equations to account for the effects of atmospheric water vapor content and sun angle. Procedures for adjusting air temperature and air vapor content data are introduced to compensate for the aridity of the weather station environment. All of the guidelines are simple and straightforward, and can serve as preliminary ''filters'' by which to scrutinize weather measurements and as near real-time data flagging procedures for agricultural weather networks.
This technical note presents an approach to irrigation and drainage canal-design procedure that uses dynamic programming where objective function and constraints are related to criteria used in canal design. The canal-design procedure is based on the principle of limiting velocities of water flow: minimum permissible velocity as a limit for sedimentation and maximum permissible velocity as a limit for erosion. The objective of the design is to determine the longitudinal slope (s) and bed width (b) of the canal in such a way that the total construction cost is minimum. This method is the first step in the development of an enhanced design. Application of the dynamic programming allows sophisticated improvements and corrections of the procedure.
The physical problem resulting in poor agricultural and economic growth in Bihar highlights the necessity for the effective and integrated development and optimal utilization of Bihar's water resources. There was only a feeble thrust until now in this direction. Bihar state suffers from both the occurrence of floods and the incidence of drought. This paradoxical syndrome has been analyzed regionwise and compared to the all-India situation. Some possible resolution aspects have also been discussed. The multidimensional complexity of the problem is a challenge to water-resource professionals, academicians, and researchers to apply their knowledge, skill, and experience to find a viable package of solutions for the economic emancipation of this economically most backward state of India.
A method was developed for designing microirrigation submain units. The lateral discharge equation was used to express the relationship between the discharge and pressure head at the inlet of a lateral to allow a submain unit to be considered as a lateral and a lateral as an emitter. The finite-element method was employed to analyze the pressure head and discharge distributions along laterals and submain. The golden section search was applied to find the operating pressure heads of the lateral and submain corresponding to the required average emitter discharge. When the required average emitter discharge, the required uniformity of water application, one parameter-either the lateral length or diameter, one parameter-either the submain length or diameter, and the field conditions are given, then the unknown parameters, the best submain position (paired laterals), and the operating pressure head of the submain unit can be accurately designed using a personal computer.
Rational evaluation of surface irrigation systems should consider the effects of spatial variations in soil intake properties on advance trajectories and on the uniformity of infiltrated depths. The objective was to quantify the effects of spatial variations in infiltration parameters on the variability of advance trajectories and on infiltration depths. The soil properties were expressed as random space functions, and small perturbation analysis was applied to analytical solutions for the advance phase. This resulted in closed-form expressions relating the variability in soil properties to the variability in advance trajectories. The expressions were tested using Monte Carlo (MC) simulations. The results show good agreement between the analytical expressions and the simulated mean and variance of advance trajectories for a wide range of intake variabilities. In all cases, a sharp increase in the variance of advance times was observed toward the end of the field. This resulted in discrepancies between the simulated and the closed-form approximation for infiltration depths at large distances from the field inlet. The study provides a predictive tool for the evaluation of management strategies for surface irrigation in heterogeneous fields once the extent of spatial variability in soil intake properties has been estimated. Some applications for the estimation of uniformity and application efficiency are illustrated.
Due to differences in infiltration characteristics across field, uniformly delivered furrow irrigation streams advance at different rates. This ''inter-row'' nonuniformity is combined with the nonuniform distribution of irrigation water along the furrow length. Unlike studies based on data from one or two representative furrows, this analysis evaluates water losses in the presence of both lateral and longitudinal variation. A spatial mathematical description of the nonuniform distribution of application depth over the whole field area is made in relative terms. Formulas for evaluation of water losses were derived by integrating both ''downfield'' and ''inter-row'' deep percolation and runoff losses. The percentage losses calculated by these formulas were compared with those assessed from one and two representative furrows and differences up to twofold were found. An algorithm was developed for model application over a wide range of field conditions. The model was calibrated for irrigation on clay and silty clay loam soils and examples were given of its use.
Critical depth is an important parameter assuming the analysis of varied flow in the canals and natural streams. Direct solution of critical depth problems is not possible, as the governing equations for practical canal sections are implicit. The solution requires tedious computations of trial and error. Tabular and graphical methods are also available for solution. These methods are subject to errors of double interpolation or error of judgment in reading the graphs. No method is available for rounded-bottom and rounded-corner canal sections. Reported herein are explicit equations for critical depths in various sections used as irrigation channels.
The problem of seepage from unlined surface canals or elongated ponds was investigated. Seepage from single or interacting canals has been computed for a variety of boundary conditions at the bottom of the seepage layer. Both the seepage rate and the free surface profile of the resulting seepage plume have been determined using the boundary element method. The boundary element method is appropriate for the solution of the types of problems investigated herein, due to the relative ease with which the location of the plume free surface can be determined. The results of this study were compared with those obtained via other solution techniques and available in the literature. The agreement was generally very good. A novel iteration technique was used for detemination of the free surface of the plume that results from seepage through a layer with free drainage at its bottom. The results for all cases that were investigated are given in graphical form for a series of typical configurations.
