Journal of Irrigation and Drainage Engineering

Hydrograph methods are used to identify functional dependencies of the rational-method runoff coefficient, and nested intensity-duration-frequency (IDF) rainfall distributions are used to evaluate the assumption that a uniform rainfall intensity with duration equal to the time of concentration leads to the maximum peak runoff rate. Key findings of this study are that the runoff coefficient can have a substantial dependence on both the IDF function and the time of concentration of the catchment, the runoff coefficient can take on values greater than one, and the peak runoff rate is underestimated by assuming a constant rainfall intensity of duration equal to the time of concentration.

There is a need for regulation and control of irrigation conveyance systems for sustainable agriculture. Design and analysis of hydraulic structures within complex channel systems are essential for conservation and efficient use of irrigation water. An improved computational model based on gradually varied flow assumptions and capable of solving discharges and water levels in complex channel network systems to include lateral weirs is presented. Results include water levels, discharge distribution, and computation of flow over or dimensions of lateral structures. The model uses the simultaneous solution method (SSM) to solve the continuity and energy equations at several channels reaches, in addition to the lateral weir equation. The nonlinear system of equations produced when applying this method is solved with the Newton-Raphson procedure. A series of successive approximations leading to the solution requires the solution of a set of linear equations. The biconjugated gradient stabilizer with preconditioner method (BiCGSTAB) is used to solve the linear system formed by large sparse matrices occurring in channel networks. Comparison of the SSM results with the standard step method (StdSM) as included in Hydrologic Engineering Center-River Analysis System (HEC-RAS) for parallel channel systems, with and without lateral structures, was excellent. The capabilities of the SSM are demonstrated solving a channel network in which three lateral weirs are designed and two more are analyzed during the same program execution. The model is easy to use, converges in a few iterations, and can be applied for design or analysis of lateral structures in irrigation engineering.

The objectives of this study are to (1) characterize the consistency of laser diffraction (LD) and automated dynamic image analysis (DIA) instruments in estimating the size of suspended peat particles in water and the sphericity of peat particles measured using DIA; (2) characterize the particle-size distribution of suspended solids in irrigation water sources from a survey of plant nurseries; and (3) analyze total suspended solids (TSS) upstream and downstream of fiber media and screen filters installed for filtration of recirculated water in commercial plant nurseries. Over 70% of peat particles had an estimated circularity value greater than 0.7, indicating a mix of elongated and spherical particles. The DIA and LD estimates of median particle diameter with circular particle-shape models yielded similar results when tested on three peat particle-size classes and two levels of TSS. TSS varied greatly in different water sources, with an average $3.3\pm 0.4\mathrm{mg}/\mathrm{L}\mathrm{mean}\pm \mathrm{standard}\mathrm{error}$, with a range of 2.5–$4.5\mathrm{mg}/\mathrm{L}$ for well water, average $4.7\pm 1.2\mathrm{mg}/\mathrm{L}$ (range of 1.6–$9.9\mathrm{mg}/\mathrm{L}$) from uncovered catchment basins, and an average of $40.0\pm 14.8\mathrm{mg}/\mathrm{L}$ (range of 2.0–$301.0\mathrm{mg}/\mathrm{L}$) from ebb-and-flood subirrigation return water, respectively. Across all water sources, TSS ranged from 1.6 to $301\mathrm{mg}/\mathrm{L}$, averaging $28\pm 10.4\mathrm{mg}/\mathrm{L}$. The suspended-particle diameter in the 10th, 50th (or median), and 90th percentiles by total particle volume was 28, 116, and 347 μm, respectively, which is relevant when considering the amount of suspended solids that are likely to be removed by filters of different micrometer sizes. Fiber media and screen filters reduced TSS by an average $57.9\pm 7.4\%$ of the prefiltration TSS. Microscopy analysis of several fiber media filters showed that the pore sizes reported by vendors were smaller than the observed particle pore sizes. Multiple filtration stages would be ideal for ebb-and-flood water because of the high and variable TSS levels observed in recirculated ebb-and-flood water samples, the wide range of particle sizes and shapes, and the average removal of approximately half the TSS by a single stage of screen or fiber media filtration.

Agricultural irrigation accounts for the largest proportion of freshwater use worldwide, and canal automation potentially improves conveyance efficiency in irrigation canal systems. In this paper, model predictive control (MPC) for a cascaded irrigation canal system was formulated using the integrator-delay model. Magnitude and variation amplitude constraints on input and output imposed on the canal operation were identified along with proposed handling methods, and optimal control actions were achieved by quadratic objective function optimization. The MPC, as well as classical proportional-integral (PI) and centralized linear quadratic (LQ) for comparison, were developed for the Changma South Irrigation District cascaded irrigation canals in Gansu Province (China) and numerically tested via SOBEK software. In contrast to the poor performance of PI and LQ in controlling the studied canal, the results show that MPC can efficiently control the canal system under known demand changes and maintain water levels at control points within the operating range. The control performance improves if normal input and output constraints are incorporated in optimization. However, deadband constraints, which is the minimum variation amplitude of input, cause controlled water levels to oscillate around the reference value and degrade the control performance. In summary, MPC can cope with time delays, coupling effects, and constraints inherent in a cascaded irrigation canals system. Furthermore, it is suggested to evaluate more advanced methods for handling the output and deadband constraints in future studies.

Irrigation of crops using water from the Savili and Mogtédo reservoirs in Burkina Faso provides an opportunity to increase rural incomes. In order to ensure the sustainability and improvement of the irrigation infrastructure, it is necessary to monitor and evaluate its technical performance. To this end, the authors evaluated crop water use efficiency, water application, and conveyance efficiencies; modeled theoretical irrigation schedules for comparison with actual irrigation schedules; and assessed overall water management. The results show that water application efficiencies were less than 20% at Savili, and between 41% and 55% at Mogtédo. Water use efficiencies ranged from 1.12 to $3.4\mathrm{kg}{\mathrm{m}}^{-3}$ for Allium cepa (onion) in three networks, $0.31\mathrm{kg}{\mathrm{m}}^{-3}$ for Zea mays (corn) at Mogtédo, and $0.34\mathrm{kg}{\mathrm{m}}^{-3}$ for Phaseolus vulgaris (green beans) at Savili. Poor irrigation management resulted in significant water loss, estimated to be $\mathrm{2,999,923}{\mathrm{m}}^3/\mathrm{year}$ for the Mogtédo and Savili sites. The main reason for this underperformance seems to be related to technical and organizational failures by producers. Strengthening local farmers’ technical and organizational capacities could help improve network performance and achieve significant water savings.

The water management of golf courses is an issue of concern in drought-prone areas that demand irrigation strategies aimed at reducing turfgrass water consumption. Deficit irrigation and summer drought are water-saving strategies that are being assessed at a research level to cope with water shortages. In this work, the response of Cynodon dactylon (L.) var. Riviera to an induced period of severe summer drought of around 75 days and the subsequent recovery was assessed at a golf course in southern Spain. The green cover (GC) fraction and the main turf quality attributes were compared during two drought/recovery cycles to well-watered turfgrass. The results show that the deficit irrigation applied before the drought period decreased the quality of the turfgrass and led to fast turfgrass quality impairment during the drought interval, reaching the lowest quality level around 40 days after the beginning of the drought period. Once irrigation recovery started, GC and turf quality levels similar to those observed before the deficit irrigation period were reached after 30 days. Also, this water management strategy was effective for the control of weeds, especially Digitaria spp.