Journal of Irrigation and Drainage Engineering

Most of the research on the design of feedback controllers for irrigation canals has been concentrated on single, in-line canals with no branches. Because the branches in a network are hydraulically coupled with each other, it may be difficult to automatically control a branching canal network by designing separate feedback controllers for each branch and then letting them run simultaneously. Thus feedback control of an entire branching canal system may be more efficient if the branching flow dynamics are explicitly taken into account during the feedback controller design process. This paper develops two different feedback controllers for branching canal networks. The first feedback controller was developed using linear quadratic regulator theory and the second using model predictive control. Both algorithms were able to effectively control a simple branching canal network example with relatively small flow changes.

Previous research on canal automation has dealt with the control of single, in-line canals, while canal operators typically have to control an entire network of canals. Because the branches in a network are hydraulically coupled with each other, control of a branching canal network based on separate controllers for each branch may not be the most effective control strategy. A methodology by which existing automatic control systems could be modified to control branching canal networks is provided in a companion paper. This paper presents results of hydraulic simulations of the new methodology to estimate the controllability of a large portion of the branching canal network operated by the Salt River Project (SRP). Two types of controllers were used for this study: (1) linear quadratic regulator (LQR) and (2) model predictive control (MPC). Both controllers used the same underlying process model [integrator-delay (ID) model], and both controllers were capable of feedback and feedforward control. Under feedback control alone, both controllers gave similar performance, but were unable to effectively control the overall system because of the long delay times. When feedforward control was added to the feedback controller, both of these control systems were able to effectively control the branching canal network operated by SRP. For the LQR controller, the volume compensation method for routing known demand change was used as the feedforward controller. For the MPC controller, the ID model was used as the feedforward controller. Slight differences were noted between the performance of the two feedforward controllers.

In preparing water allocation schedules for fields in a lateral unit, the time required for water to travel from one point on a lateral to another can be significant and is dependent on the sequence in which users abstract water. This paper illustrates the problem of ignoring travel time and/or considering travel time to be sequence independent. For two users, each requesting water for a duration of 4 h, by assuming travel time to be sequence independent, one user receives water for 5 h, a 25% increase, and the other receives water for only 3 h, a 25% decrease. This paper presents a formulation of the irrigation scheduling problem for sequential users with sequent dependent travel time. The formulation is implemented as an integer program and applied to part of a lateral unit on the Juan Distributary, Haryana, India. Two models are presented, the first of which allows for noncontiguous jobs, i.e., idle time is permitted between jobs. The second model does not permit noncontiguous jobs.

In this study optimal irrigation planning strategies are developed for the Nagarjuna Sagar Right Canal command in the semiarid region of South India. The specific objective of the study is to allocate the available land and water resources in a multicrop and multiseason environment and to obtain irrigation weeks requiring irrigation of a fixed depth of 40 mm. The problem is solved in four stages. First, weekly crop water requirements are calculated from the evapotranspiration model by the Penman-Monteith method. Second, seasonal crop water production functions are developed using the single-crop intraseasonal allocation model for each crop in all seasons. Third, allocations of area and water are made at seasonal and interseasonal levels by deterministic dynamic programming, maximizing the net annual benefit from the project. And fourth, once optimal seasonal allocations have been attained, irrigation scheduling is performed by running a single-crop intraseasonal allocation model. Optimal cropping pattern and irrigation water allocations are then made with full and deficit irrigation strategies for various levels of probability of exceedance of the expected annual water available. The results reveal that the optimization approach can significantly improve the annual net benefit with a deficit irrigation strategy under water scarcity.

Reference crop evapotranspiration $\left({\mathrm{ET}}_0\right)$ is a key variable in procedures established for estimation of evapotranspiration rates of agricultural crops. In recent years, there is growing evidence to show that the more physically based FAO-56 Penman–Monteith (PM) combination method yields consistently more accurate ${\mathrm{ET}}_0$ estimates across a wide range of climates and is being proposed as the sole method for ${\mathrm{ET}}_0$ computations. However, other methods continue to remain popular among Indian practitioners either because of traditional usage or because of their simpler input data requirements. In this study, we evaluated the performances of several ${\mathrm{ET}}_0$ methods in the major climate regimes of India with a view to quantify differences in ${\mathrm{ET}}_0$ estimates as influenced by climatic conditions and also to identify methods that yield results closest to the FAO-56 PM method. Performances of seven ${\mathrm{ET}}_0$ methods, representing temperature-based, radiation-based, pan evaporation-based, and combination-type equations, were compared with the FAO-56 PM method using historical climate data from four stations located one each in arid (Jodhpur), semiarid (Hyderabad), subhumid (Bangalore), and humid (Pattambi) climates of India. For each location, ${\mathrm{ET}}_0$ estimates by all the methods for assumed hypothetical grass reference crop were statistically compared using daily climate records extending over periods of 3–4 years. Comparisons were performed for daily and monthly computational time steps. Overall results while providing information on variations in FAO-56 PM ${\mathrm{ET}}_0$ values across climates also indicated climate-specific differences in ${\mathrm{ET}}_0$ estimates obtained by the various methods. Among the ${\mathrm{ET}}_0$ methods evaluated, the FAO-56 Hargreaves (temperature-based) method yielded ${\mathrm{ET}}_0$ estimates closest to the FAO-56 PM method both for daily and monthly time steps, in all climates except the humid one where the Turc (radiation-based) was best. Considering daily comparisons, the associated minimum standard errors of estimate (SEE) were 1.35, 0.78, 0.67, and 0.31 mm/day, for the arid, semiarid, subhumid, and humid locations, respectively. For monthly comparisons, minimum SEE values were smaller at 0.95, 0.59, 0.38, and 0.20 mm/day for arid, semiarid, subhumid, and humid locations, respectively. These results indicate that the choice of an alternative simpler equation in a particular climate on the basis of SEE is dictated by the time step adopted and also it appears that the simpler equations yield much smaller errors when monthly computations are made. In order to provide simple ${\mathrm{ET}}_0$ estimation tools for practitioners, linear regression equations for preferred FAO-56 PM ${\mathrm{ET}}_0$ estimates in terms of ${\mathrm{ET}}_0$ estimates by the simpler methods were developed and validated for each climate. A novel attempt was made to investigate the reasons for the climate-dependent success of the simpler alternative ${\mathrm{ET}}_0$ equations using multivariate factor analysis techniques. For each climate, datasets comprising FAO-56 PM ${\mathrm{ET}}_0$ estimates and the climatic variables were subject to factor analysis and the resulting rotated factor loadings were used to interpret the relative importance of climatic variables in explaining the observed variabilities in ${\mathrm{ET}}_0$ estimates. Results of factor analysis more or less conformed the results of the statistical comparisons and provided a statistical justification for the ranking of alternative methods based on performance indices. Factor analysis also indicated that windspeed appears to be an important variable in the arid climate, whereas sunshine hours appear to be more dominant in subhumid and humid climates. Temperature related variables appear to be the most crucial inputs required to obtain ${\mathrm{ET}}_0$ estimates comparable to those from the FAO-56 PM method across all the climates considered.

Water quality in the Middle Coastal Plain of North Carolina has been impacted by agriculture; however, the water quality impacts in these areas over time have not been studied in detail. The surface water quality of several streams in the Neuse River Watershed along the Middle Coastal Plain of North Carolina was monitored for approximately five years, while shallow groundwater in cropped fields and adjacent to drainage ditches was monitored for three years. Surface water samples were collected biweekly and analyzed for nitrate nitrogen $\left(\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}\right)$ , ammonium nitrogen $\left(\mathrm{N}{\mathrm{H}}_4\text{-}\mathrm{N}\right)$ , total Kjeldahl nitrogen, orthophosphate $(\mathrm{P}{\mathrm{O}}_4-\mathrm{P})$ , total phosphate, and total suspended solids, and approximately monthly groundwater samples were collected from wells and analyzed for $\mathrm{N}{\mathrm{O}}_3-\mathrm{N}$ . Trends relating to seasonal changes in stream water quality as a function of land use and soil type were analyzed, as well as long term changes. Generally, upstream sampling points showed low levels of all constituents. Nutrient and sediment concentrations increased along the streams draining the agricultural lands. Trends in surface water quality did not change under row crops, and $\mathrm{N}{\mathrm{O}}_3-\mathrm{N}$ averaged $3.4–4.1\mathrm{mg}∕\mathrm{L}$ , while $\mathrm{N}{\mathrm{H}}_4-\mathrm{N}$ averaged $0.1\mathrm{mg}∕\mathrm{L}$ . Surface water was impacted dramatically by seepage from an anaerobic swine wastewater lagoon. $\mathrm{N}{\mathrm{O}}_3-\mathrm{N}$ and $\mathrm{N}{\mathrm{H}}_4-\mathrm{N}$ downstream from the seepage plume averaged 1.5 and $12.7\mathrm{mg}∕\mathrm{L}$ , respectively. Directly down gradient of the lagoon, groundwater samples averaged $121\mathrm{mg}∕\mathrm{L}$ for $\mathrm{N}{\mathrm{H}}_4-\mathrm{N}$ . Groundwater $\mathrm{N}{\mathrm{O}}_3-\mathrm{N}$ concentrations decreased 30–76% due to a reduced zone along many of the ditches. Biomass production in the drainage ditches resulted in substantial amounts of organic nitrogen in the ditches. Surface water nitrate concentration averaged at or above the limit for new wastewater treatment plants on the Neuse River. Groundwater nitrate concentration in the shallow groundwater averaged $4.6–9.3\mathrm{mg}∕\mathrm{L}$ ; however, in several locations on the farm, groundwater nitrate nitrogen concentration was elevated above the $10\mathrm{mg}∕\mathrm{L}$ U.S. Environmental Protection Agency limit for drinking water due to fertilization of crops and pastures. Hurricanes in 1999 flushed nutrients out of the soil profile in areas that were flooded along the river.

This study presents both a numerical and an experimental solution to seepage from a rectangular ditch or elongated pond to a groundwater table of infinite horizontal extent. Because of the unknown location of the free surface, the flow domain is transformed into the complex potential plane using the inverse formulation method, where the free surface becomes a straight line. The method of finite differences was used to solve the boundary value problem. The problem was also investigated experimentally using a sand tank model. For comparison purposes, a one-dimensional analytical solution is also presented. The results were compared with each other and with those available in the literature obtained with other solution techniques. The parameters affecting the seepage rate were investigated and the resulting relationships are presented in dimensionless graphs. It is believed that these graphs may be of use in design problems. The conditions for which the simplified one-dimensional analytical solution agrees well with the results of the sophisticated two-dimensional numerical solution are identified.

A series of laboratory experiments was performed in order to investigate the effects of width of the lower weir crest and step height of broad-crested weirs of rectangular compound cross section on the values of the discharge coefficient, the approach velocity coefficient, and the modular limit. For this purpose, nine different broad-crested weir models with rectangular compound cross sections and a model with a rectangular cross section were tested in a horizontal laboratory flume of 11.0 m length, 0.29 m width, and 0.70 m depth for a wide range of discharges. The compound cross sections were formed by a combination of three sets of step heights and three sets of lower weir crest widths. The sill-referenced heads at the approach channel and at the tailwater channel were measured in each experiment. The dependence of the discharge coefficient, approach velocity coefficient, and modular limit values on model parameters was investigated, and these quantities were compared with those of the broad-crested weir models with a rectangular cross section.

A diagnostic curve is developed for identification of dispersivity and injected mass in case of homogeneous and isotropic soil. The exit concentration from a soil column experiment is diagnostically plotted and matched to the diagnostic curve to yield the estimates of dispersivity and injected mass. A changed value of dispersivity can be identified during increasing versus decreasing concentrations. The new method is applicable for any value of the Péclet number or specific dispersivity. An estimate of the injected mass would be helpful in assessing the pollutant load from a point source. Thus, the new method would be useful for field application.

The probe of a commercial thermal groundwater flowmeter was evaluated in the laboratory to determine the causes of apparent inaccurate results from field experiments conducted under high groundwater velocities in a gravel and coarse sand soil. The test was performed with water velocities from 2.3 to 103 m/day. Errors as large as 40% arose in the magnitude and direction of velocities within the measuring range specified by the manufacturer. The poor cosine response of the thermal sensor axes was found to be a major source of errors, because the accuracy of the velocity vector depends strongly on the angular response of the thermal sensor axes. This was partially corrected with a set of coefficients determined from laboratory tests.

An investigation to study the effects of slope and vegetative cover on outflow, sediment concentration, and deep percolation in channels covered with Bermuda grass in an alfisol was conducted using a hydraulic tilting flume, at the Central Research Institute for Dryland Agriculture, Hyderabad, India. Vegetative covers of 25, 50, 75, and 100% were chosen for the experiment with bare-soil condition as control for 1–5.0% bed slope. It was seen that in bare soil conditions the mean sediment concentration in the outflow increased by 5 times at 5% slope compared to 1% bed slope. Introduction of vegetative covers reduced the sediment concentration and increased the water infiltration considerably compared to the control. The study indicates that 25% vegetative cover may be acceptable for 1.0% land slope and at higher slopes higher percentages of vegetative cover may be recommended. When the interaction between the slope and vegetative cover was taken into account it was preferred to go to 25% vegetative cover at the beginning and allow the vegetation to develop to 100% cover in due course. This technique will simplify and economize the process of constructing grassed waterways.

Block ramps or rock chutes are stream restoration structures used in many hydraulic projects. If the base material presents stability problems, a reinforcement can be used; it consists of placing over the ramp rocks greater in size than the base material in order to increase the flow resistance and reduce the shear stresses on the base material. The presence of these boulders also changes the energy dissipation of the flow over the structure. This work shows the results of experimental tests conducted on reinforced block ramps with slopes varying from 0.08 to 0.33. The effect of the various geometric parameters has been investigated. The aim is to extend existing relationships for a simple block ramp and define a new equation that can be applied to a block ramp with or without the presence of boulders.

An optimization method for estimating an optimal smooth instantaneous unit hydrograph (IUH) from multistorm data taken simultaneously is proposed. A gamma IUH is used for representing the analytical IUH. The parameters of the analytical IUH are optimized. The method avoids oscillations in the tail end of IUH. It automatically takes care of the volume and nonnegativity constraints. The application of the method is illustrated through examples. The new method reliably estimates the optimal IUH.