Journal of Irrigation and Drainage Engineering

A lateral canal in a southwestern U.S. irrigation district was instrumented for continuous monitoring. Deliveries were flexibly scheduled; farmers arranged timing, rate, and duration with the district. The distribution of measured variables showed that the lateral was operated under a wide variety of demand and operational conditions and that farm delivery flows were frequently not uniform due to changing conditions along the lateral. Flows that are unpredictably variable affect the performance and evaluation of on‐farm application systems and, unless controlled, can negate the benefits of flexible scheduling (more precise management). Statistical analysis of 286 deliveries to nine farm turnouts indentified a number of sources of nonuniform flows which were a combination of canal hydraulics and operational characteristics. Time of year that deliveries occurred was shown to affect uniformity, as were median flow rate, delivery duration, and location of turnouts, both within a pool between two check structures and along the lateral. Identifying sources of nonuniformities is an important first step in devising structural and operational controls to improve delivery uniformity.

An irrigation‐scheduling model was developed based on soil‐water budgeting, which incorporates the contribution of shallow‐groundwater tables (GWT) to crop‐water use and the effects of soil restrictions on crop rooting. Capillary flux of water from the groundwater table was estimated with a form of Darcy's equation, assuming mean soil water potential gradients between irrigations. Crop‐water use was estimated with a grass‐reference evapotranspiration $\left({\mathrm{ET}}_0\right)$ and crop coefficients $\left(K_c\right)\text{.}$ Water uptake was partitioned into the contributions of various soil zones based on root distribution. The model inputs are: soil variables (available water, allowable depletion, GWT depth, moisture‐characteristic curve, and unsaturated hydraulic conductivity); crop variables (root distribution, $K_c$ curve); and climate $\left({\mathrm{ET}}_0\right)\text{.}$ The model estimates irrigation interval, amount of water to apply per irrigation, and water contributed by the GWT. Scheduling the irrigation of wheat based on the model reduced seasonal irrigations by 28% and water application by 24%, compared with the conventional weekly irrigation.

A physically based model for the management and forecasting of irrigation water requirements at an on‐farm level is developed. The model includes mechanisms for simulating root and soil‐water movement, root growth, and crop yield. Model inputs and soil and crop parameters are easily attainable so that the model is usable in field situations. The management model is verified by calibrating it to a crop of cotton grown on an experimental plot at the University of California at Davis, then comparing the results of the model simulations to the field measured data for two alternate water treatments that were used to irrigate the experimental cotton crop. These verifications indicate that the soil‐water content distributions are simulated with a high degree of accuracy, and root‐density distributions are better simulated under moist soil conditions. Further analysis indicates that maintaining moist soil conditions during the bloom stage of cotton growth is critical for consistently high cotton crop yields.

A new method for the optimal real‐time control of water transport in open channels, called ${\mathrm{DYN}}^2\text{,}$ is presented. This method was developed for controlling a class of water conveyance systems where so‐called dynamic regulation (DR), proposed by the Société du Canal de Provence (France), is the basic control method. The DR concept is based on the heuristic policy, which compensates for downstream cumulative volume error. In ${\mathrm{DYN}}^2\text{,}$ however, optimal control theory is applied to solve the water‐transport control problem more precisely than would be possible using the heuristic approach. Applying dynamic programming (DP) to DR, the ${\mathrm{DYN}}^2$ method was derived—thus the name ${\mathrm{DYN}}^2\text{.}$ Advantages of DYN2 over DR are described. Both the ${\mathrm{DYN}}^2$ and DR have been applied on the Strezevo irrigation system (in Southern Yugoslavia, near Greece), resulting in the development of a state‐of‐the‐art computer‐based supervisory control and data acquisition (SCADA) system. In this system, a computer makes decisions based on either DR or ${\mathrm{DYN}}^2$ methods (depending on the operator's choice) and automatically controls system operations (closed‐loop system). The objective is minimizing water loss and volume errors in canal reaches while meeting a number of constraints in the system.

This study develops a simple analytical model, using the volume balance approach, to simulate all phases of border irrigation. The surface and subsurface flow profiles in the advance phase are assumed to be of parabolic shape, and their coefficients are determined by conditions in the gradually varied flow region, rather than in the rapidly varied flow region near the advance front. The recession phases are simulated by using a simple iterative method based on Strelkof$\acute{f}$s assumption, taking into account time‐varying infiltration. Only one observed data set was used to calibrate the model, and 29 different observed data sets were used to verify the model. A comparison with some existing models shows that the model is simpler, more accurate (with less than 7% prediction error for all phases of the 29 test borders), and easier to apply.

Evapotranspiration from cool‐season grasses is used as the reference for $\mathrm{ET0}$. The requirements for local calibration for three equations for $\mathrm{ET0}$ recommended by the Food and Agriculture Organization of the United Nations (FAO) are shown for different climatic regions of California. Data from measured coolseason‐grass evapotranspiration and Class A pan evaporation from sites located in large well‐watered, irrigated grass pastures in three distinct climatic conditions are used to evaluate a method for estimating $\mathrm{ET0}$ that requires only measured values of maximum and minimum air temperatures. Mean temperature, minimum relative humidity, and solar radiation can all be estimated from maximum and minimum air temperatures. The equation for $\mathrm{ET0}$ that requires only temperature measurements may seem to be quite simple, but it is in reality a very comprehensive procedure incorporating most of the climatic interactions that influence the evaporative potential. The analysis of data from four lysimeter and Class A pan sites in California indicates that the temperature‐range equation estimates $\mathrm{ET0}$ reasonably well in a large diversity of climates. The corrected Penman and other equations recommended by FAO are shown to usually overestimate $\mathrm{ET0}$ in various climatic regions of California.

Complete and equally spaced river quality variables specific conductance (SPC, $\mu S{\mathrm{cm}}^{-1}$), total dissolved solids (TDS, $\mathrm{mg}{L}^{-1}$), and the logarithm of the daily discharge mean (DDM, $m^3{s}^{-1}$) are used in frequency domain modeling. Significant autocorrelation values at lags 1 and 12 indicate that the observations are not random and have a yearly periodicity. Cross‐correlations also indicate the yearly periodicity as well as a negative relationship between TDS and DDM, and SPC and TDS. The cross‐correlation is positive between SPC and TDS. The spectral and cross‐spectral analyses show a significant periodicity at a frequency of ${\nu }_k=0.078$ cycles per month, or a period of one year. Because these variables are linearly correlated, an impulse response function can be used to determine the lagging, leading, and/or immediate response of the input(s) on the output. It is found that the best predictor of SPC is DDM. The small contribution from TDS is ignored. Significant coherence and F statistic at a frequency of 0.093 confirms the strong linear relationship between these two variables.

Rapid irrigation development in the Sudan has stretched to the limit its share in the Nile waters. Significant savings on irrigation water can be made by improved water management. Accurate estimation of crops evapotranspiration, ET, is a prerequisite. ET was estimated by predicting first reference crop evapotranspiration. Grass was selected as the reference crop. FAO‐Penman with Penman (1948) wind function for clipped grass was ranked first among the methods selected to predict grass ET. Using the crop coefficients of Doorenbos and Kassam (1979), ET for cotton, groundnuts and wheat grown in the Gezira scheme were then predicted. Predicted and measured ET remained well within $\pm 15\%\text{.}$ For air temperature higher and lower than 28.3° C, it was found that warm‐season grass ET was equal to 1.0 and 0.635 ET of cool‐season grass, respectively. Because of this temperature effect, care must be taken not to use these two grass varieties indiscriminately to estimate crop ET.

This paper presents a practical linear proportional weir of simple geometric shape in the form of an inverted V‐notch or inward trapezium. The flow through this weir, of half‐width w and altitude d, for depths above $0.22d$ is proportional to the depth of flow measured above a reference plane situated at $0.08d$ for all heads in the range $0.22d⩽h⩽0.94d\text{,}$ with a maximum percentage deviation of $\pm 1.5$ from the theoretical discharge. The linear relationship between head and discharge is based on numerical optimization procedures. Nearly 75% of the depth of inverted V‐notch can be used effectively as the measuring range. Experiments with four weirs, with different vertex angles, show excellent agreement with the theory by giving an average coefficient of discharge for each weir varying from 0.61–0.62.

Agriculture accounts for nearly two‐thirds of the gross domestic product of Nepal, one of the least developed countries of the world. Thus, irrigation is important to sustaining the country's economy. While irrigation has been practiced for decades, there is considerable need both to expand the currently irrigated area and to improve the efficiency of existing systems. There is no question that for the future economic development of an agrarian country like Nepal, irrigation development and management must play an important part. This paper reviews the potential of large‐ to medium‐size irrigation projects in the Terai, small‐size irrigation projects in the hill areas, groundwater development, farmer‐managed irrigation systems, and rehabilitation of existing irrigation projects. The role of irrigation as a means of expansion of production and income of the country and institutional implications is also discussed. It should, however, be noted that before major irrigation projects can be developed, treaties with India have to be negotiated for using the waters of international rivers. Thus, realistically, it is somewhat unlikely that major developments will occur before the year 2000.