Journal of Irrigation and Drainage Engineering

A zero‐inertia (ZI) model for irrigation advance in furrows (ZIFA) is developed. It is based on an analytical solution of the ZI differential equations and accounts for three principally different approaches to describe adequately the various types of furrow shapes. ZIFA takes into account the varying character of infiltration and does not contain any restriction for modeling the infiltration phenomenon. Besides simulation of advance flow in level or sloping borders with variable inflow, ZIFA provides also the possibility to remove two weak points in rigorous numerical modeling, namely to replace both the approximate Witham solution for generating initial values as well as cumbersome mass‐balance techniques used to describe the flow in the tip region of the advancing wave. ZIFA compared very favorably to a full hydrodynamic model as well as to field data and the outcome of a numerical ZI model.

Qualitative and quantitative aspects of both the surface and subsurface drainage in the city of Riyadh, in the Kingdom of Saudi Arabia, are studied with a view to (1) Determining the resuse potential; and (2) estimating the magnitude of the problem of the rising water table. Five gaging and sampling stations are established at the outfalls of the city's drainage network, and the quality and quantity of both storm runoff as well as dry‐weather flow are monitored over a period of six years. The quality and quantity of this drainage is such that it is well within reuse schemes, most notably for irrigation purposes. Treatment schemes for reuse of this drainage water for irrigation and industrial purposes are proposed. The primary cause of the water‐table rise is also identified.

A procedure is presented to estimate probabilistic irrigation requirements for lowland rice cultivation. The procedure uses a water‐balance equation in which rainfall and evapotranspiration are considered as stochastic variables. The Leaky law, total probability theorem, and SMEMAX and power transformations were tried to estimate weekly rainfall and normal distribution for estimating weekly evapotranspiration. Because of the zero values in the weekly rainfall data series, the Leaky law was found to be most appropriate to describe the rainfall amounts and normal distribution for evapotranspiration data series. Rainfall and evapotranspiration values were later used to estimate weekly irrigation requirements through the water‐balance equation. When applied to an irrigation system in Thailand, this model gave satisfactory results, and showed that a significant amount of water can be saved during the rainy season even when the system is operated at relatively high probability (or reliability) levels.

Sluice‐gate discharge coefficient is an involved function of geometric and hydraulic parameters. For free flow, it is related to upstream depth and gate opening, whereas for submerged flow, in addition to these parameters, it depends on tail‐water depth. The present practice of discharge coefficient determination is from curves drawn relating discharge coefficient and upstream‐depth gate‐opening ratio with tail‐water‐depth gate‐opening ratio being the third parameter for submerged flow. This method lends itself to sufficient error of judgment due to interpolation between two types of curves. Furthermore, the graphical information cannot be used for any analytical and/or numerical method for flow control and flow profile determination. In this paper high‐accuracy discharge coefficient equations for free and submerged flows have been developed along with the criterion for determination of free and submerged flow. Procedures for solution of various gate‐opening problems have also been given.

Open‐channel expansions for subcritical flows are encountered in the design of hydraulic structures such as aqueducts, superpassages, and so on. In these structures the flow tends to separate while subjected to the positive pressure gradient associated with flow deceleration, thus resulting in a considerable loss of energy. Considerable savings could be achieved if the transition is designed by minimizing the head loss incurred in it. In this paper which applies the optimal‐control theory, a methodology for the design of an expansive transition between a rectangular flume and a trapezoidal channel for a subcritical flow was evolved. Analyzing a large number of designed optimal transitions, empirical equations for the bed‐width and side‐slope profiles were obtained.

A simulation model is presented for planning the conjunctive use of irrigation water from a single multipurpose reservoir and an aquifer, and the allocation of cropped areas within an irrigation district. The model considers cropping patterns, profits for the farmers in the irrigation district, monthly reservoir and aquifer operating schedules for a one‐year planning horizon, and hydropower generation. The model reproduces the performance of the irrigation system under the management policies specified by the planners themselves, given certain initial conditions, hydrological and economic input parameters, cropping patterns, reservoir and aquifer releases, and structural characteristics. Solution to the irrigation‐planning simulation model is obtained through the use of a computer program module developed for a microcomputer. The capability of the simulation model is illustrated by applying it to planning the management of an irrigation district in northern Mexico. The model permits the study of alternative cropping patterns in the irrigation district and yields the monthly schedule of reservoir storages and releases and aquifer withdrawals as well as the annual profit in the district.

Due to the widespread use of ground water as a supply of drinking water in the United States, predicting the effect that nonpoint sources of contamination have on the quality of nearby ground‐water supplies is an important element in ensuring that public health standards are met. A variety of methods have been developed to simulate this phenomenon, but most assume that the soil system can be simulated as a homogeneous environment, which in many cases is not true. Thus, a probabilistic modeling piocedure is developed that simulates the average movement of contaminants from nonpoint sources of contamination toward an underlying aquifer's water table through a heterogeneous soil environment. The proposed modeling procedure is applied to a hypothetical nonpoint‐source contamination problem, and the results are compared to those of a conventional deterministic contaminant transport model. The results of this application demonstrate that the proposed procedure provides superior simulation results as compared to the deterministic model, which emphasizes the need to account for heterogeneous soil conditions found in natural environments when simulating nonpoint‐source contamination problems.

A laboratory study is conducted to measure Darcy‐Weisbach roughness coefficients for selected gravel and cobble materials. Varying rates of flow are introduced into a flume in which a given size class of gravel or cobble material is securely attached. Roughness coefficients are calculated from measurements of discharge rate and flow velocity. The laboratory data are used to develop regression equations for relating roughness coefficients to surface cover and Reynolds number. The regression relations, which are developed for values of the Reynolds number from approximately 500 to 16,000, are tested using hydraulic data collected on surfaces containing a distribution of size classes. Close agreement between predicted and measured Darcy‐Weisbach roughness coefficients is obtained by adding the roughness contributions of individual size classes. Equations are also presented for estimating surface cover from measurements of gravel and cobble mass. Accurate prediction of roughness coefficients for gravel and cobble surfaces will improve our ability to understand and properly model upland flow hydraulics.

Field data of water‐table depth fluctuations under cotton grown in Egypt arc used to relate water‐table depth frequency of occurrence to yield. Daily water‐table levels are measured. A multiple linear regression analysis is used to develop site‐specific population parameters that allow evaluation of the effect of various water‐table depths on yield. Low water tables and high water tables affect yields in different ways, and both effects can be represented. The procedure for analysis of the data is illustrated with an example. The potential use of the method is to determine drain spacings that will keep water‐table fluctuations within limits that result in the best yields.

A method is developed for estimating peak runoff rates and return periods from agricultural watersheds by analyzing precipitation and runoff data, and by using the CREAMS model. Dimensionless Huff curves are used with the CREAMS model to synthesize the frequency distribution of peak runoff rates from an experimental watershed at Coshocton, Ohio. The frequency distributions of synthesized and observed peak flows are found to correspond to each other. A sensitivity study of some model inputs showed that the method is insensitive to some uncertain inputs, which is a desirable feature. Although the method has several desirable features for practical application, it must be investigated further on watersheds in different geographic and climatologic regions before it can be widely applied.

Previously, surface irrigation hydraulic models used the principle of mass conservation to simulate the advance of water along the field and to solve the inverse problem of finding the infiltration function from measurements of advance. A flow rate rather than a volume balance theory, in combination with an advance function that is more physically realistic than the usual power function, is introduced, in which the Horton equation is used to describe infiltration, $Q_{\mathrm{in}}={\mathrm{Ax}}^{\prime }\left(t\right)+{\int }_0^{t}I(t-u)x^{\prime }\left(u\right)\mathrm{du}\text{.}$ In this equation, $Q_{\mathrm{in}}$ is the inflow rate per furrow or per unit width of border; A is the average cross‐sectional area of the stream; $x^{\prime }\left(t\right)$ is advance rate at irrigation time t; I is infiltration rate from Horton's equation; u is advance time to position x; and $t-u$ is intake‐opportunity time at x. An exponential advance rate function emerges from the solution of the flow rate equation. Furthermore, the inverse problem is solved in the same manner, a given exponential advance rate function leads to the determination of a Horton law infiltration function. The resulting advance rate, if expressed as a function of distance $[x^{\prime }=f(x\left)\right]\text{,}$ shows two distinctive linear decreasing parts from which infiltration parameters as well as surface storage emerge.

The relationship between Kostiakov and modified Kostiakov infiltration parameters and the parameters of several other infiltration equations are analyzed and discussed from a theoretical and practical point of view. Kostiakov parameters are also shown to be related to soil properties in a way that allows irrigation engineers to take advantage of existing data bases and ongoing infiltration research. It is suggested that the power parameter in both the modified and original Kostiakov relationship should be fixed at one‐half and not subject to calibration or optimization using field data. This results in relationships with some theoretical basis, parameters that are consistent with other infiltration equations and in most cases little if any loss of accuracy in the calculation of infiltration or surface hydraulics in irrigated borders.

Low‐pressure irrigation systems are developed to reduce energy requirement and cost. A consequence of low pressure is a reduced sprinkler wetting coverage. Small wetting coverages cause high water application rates and surface runoff potential. Trail tubes are perforated polyethylene hoses designed to replace sprinklers and reduce surface runoff potential in low‐pressure irrigation conditions. Long tube length can be used to create large wetting coverage to reduce surface runoff potential. Previous design of trail tubes emphasized on variable hole‐spacing tubes. Such a design produced minimum tube length and material cost. Constant hole‐spacing tubes will be longer than variable hole‐spacing tubes but have manufacturing and installation advantages. In practice, such advantages can more than offset the additional material cost due to longer tubes. Therefore, the study of constant hole‐spacing design is needed to provide an alternative selection of trail tubes. In this paper, the hydraulics of constant hole‐spacing tubes are described. Laboratory measurements are conducted to evaluate theoretical results including tube elevation, tube discharge, and water pressure. A computer program is developed to facilitate the selection of hole spacings on trail tubes.

Geostationary operational environmental satellite (GOES) infrared (IR) images and rain gauge measurements are used to study five convective storm events in Florida. The study region is divided into a training area and a test area. An approach is initiated in this study to identify rainfall areas within GOES images using the coldest cloud‐top temperature (CCTT) and the standard deviation of cloud‐top temperatures (STD‐DEV) within a group of pixels. A threshold value of satellite‐derived cloud‐top temperature is used to define the cloud‐covered areas. GOES IR images are then divided into two categories: expanding cloud images and contracting cloud images. The Bayesian optimal classifier using CCTT and STD‐DEV is implemented to further classify the cloud pixels in each category into precipitation‐free cloud pixels and precipitating cloud pixels. Cutoff rain rates from the gauge measurements are used to define the actual precipitation‐free and precipitating pixels. The results show that the classification accuracies are about 73% in the training area, and 63% in test area.

A method for obtaining the Kostiakov equation parameters for the different U.S. Soil Conservation Service (SCS) infiltration families is given along with the results. The deviation functional integrated over period of time up to the incipience of the terminal intake rate is minimized with respect to the Kostiakov parameters. Results give Kostiakov functions equivalent to SCS infiltration families and the differences in predictions of infiltration amounts between the two formulas are minimal over relatively large intervals of time. The equivalent Kostiakov parameters thus obtained and presented will be useful in irrigation modeling when only SCS family numbers for the soils are known with regard to infiltration data.