Journal of Irrigation and Drainage Engineering

Investigating the efficiency of irrigation networks is one of the most crucial factors in providing the information needed to improve the efficiency of these systems. Due to the recent water crisis in Iran, it should be considered by managers and planners in this area. Therefore, in this study, the linear robust data envelopment analysis (LRDEA) method, which has the potential to apply uncertain conditions for the model data, is used to evaluate the efficiency of four irrigation networks in the Karun catchment located in Khuzestan province, Iran. The use of this model depends on determining the appropriate input and output data that were examined. On the other hand, to study the effect of water and soil resources’ quality on the efficiency of these networks, two scenarios with and without considering the quality of these resources in the input data are considered. The results show that the addition of water and soil quality input data causes some networks to experience a significant increase in efficiency score, resulting in a significant difference between the rankings in the two scenarios; so that the average efficiency of networks in the first scenario was 0.8 and in the second scenario is 0.97. It is also found that there is a significant difference between actual and desirable use for both input data of maintenance costs and personnel, which has led to inefficiencies in networks. This difference is less in the second scenario and is calculated as 41% and 34% for maintenance costs and personnel, respectively. Examining the Monte Carlo simulation results shows that LRDEA is reliable in terms of applying uncertain conditions and using its results to improve the efficiency of networks.

Abstract

Effects of bed material and downstream flow depth on bed evolution in a right-angled channel confluence were studied through laboratory experiments. Velocity field, water surface elevation, and bed profile were measured intermittently until the flow attained equilibrium. Sediment discharges at various locations of the confluence were estimated from bed levels. Six prominent bedforms were identified, and their characteristics were quantified. The sediment discharges from different channels were initially high but decreased to approximately zero as the flow attained equilibrium. Downstream flow depth influenced overall sediment transport in the system, including the main features of bed morphology. Overall erosion in the confluence reduced as the particle size of the bed material increased. In addition, the maximum scour depth occurred at the confluence edge, and, due to the sharp corner of the confluence, its location did not change with time. Results from the present experimental study can help validate numerical models and assist in the design of a right-angled confluence.

Practical Applications

This study is related to the hydraulics of man-made confluences with mobile beds and can be useful in the following practical applications. More accurate numerical models to predict maximum scour, bed morphodynamics, and sediment transport in man-made confluences can be developed using the detailed bed profile measurements at different time instants presented in this study. Note that available numerical models use sediment discharge formulas (e.g., Meyer-Peter-Muller, Van Rijn), which are for sediment flows in straight channels. The interplay between the three-dimensional flow field, developed bed shear stress, and sediment discharge can be explored. In addition, A man-made confluence with the mobile bed can be designed with findings from the present study. The bedforms corresponding to equilibrium flow depend on discharge ratio, confluence angle, flow conditions at the exit channel, and bed material characteristics. The major bedforms can be incorporated into the confluence geometry.

Digital twin (DT) models can mirror irrigation canal systems and monitor the hydrodynamic processes in real-time to help create scheduling schemes. As for the DT model of the open channel, an important parameter that needs to be calibrated is Manning’s roughness coefficient ($n$). To establish a refined and high-fidelity DT model, the spatial variability of $n$ along the longitudinal direction needs to be considered. Parameter optimization or identification method can estimate the values of $n$ in different longitudinal segments along the canals. However, the existing relevant studies overlook the hydraulic conditions and estimation accuracy in canal segmentation. Therefore, this study proposes a comprehensive segmentation scheme for roughness estimation of irrigation canal systems. Particularly, a practical real-time segmented estimation (SE) framework using the ensemble Kalman filter (EnKF) is proposed and embedded into the DT model calibration. Verified by two canal reaches and two real-world cases, our results show that, compared with the empirical equation, the SE with the EnKF improves the model prediction accuracy by 45%–60%, especially for the canal reach longer than 10 km. This study provides a generic means for DT model calibration of irrigation canals, leading to more refined and precise monitoring and prediction of hydraulic variables.

The investigation of bedform configurations and their migration manifest under varying flow conditions in alluvial channels remains a persistent challenge for engineers and researchers due to the intricate nature and lack of certainty associated with these formations. The study of turbulence characteristics of flow over a dune-shaped bedform can become a foundation for evaluating potential bedform migration and sediment transport behavior in an alluvial stream. Through the present study, effort has been made to demonstrate the variation in turbulent anisotropy associated with the flow over a 2D fixed dune-shaped bedform under the influence of downward seepage. Using an acoustic doppler velocimeter, measurements of flow velocities were taken over several sections of the dune-shaped bedform, in the presence and absence of downward seepage. Flow characteristics at these sections are then compared for both conditions to observe the change in turbulence behavior under the influence of downward seepage. The results reveal that, at the initial sections and lee side sections of the dune, the average contribution of streamwise and spanwise turbulent intensity to turbulent kinetic energy (TKE) along the depth of flow increases by $\sim 24\%–45\%$ and $\sim 7\%–39\%$ for 10% seepage and by $\sim 26\%–63\%$ and $\sim 25\%–45\%$ for 15% seepage, respectively, as compared with the no-seepage condition. The contribution of vertical turbulent intensities to the TKE is negligible as compared with the streamwise and spanwise turbulent intensities. Similarly, the contribution of Reynolds shear stress to TKE increases by $\sim 2\%–30\%$ for 10% seepage and $\sim 5\%–35\%$ for 15% seepage at the initial sections and lee side sections of the dune as compared with the no-seepage condition. The findings from the three anisotropy tensor eigenvalues indicate a significant rise in the strength of turbulent intensities in the streamwise direction with downward seepage primarily in the region near to the bedform surface and at the initial and lee sections of the dune. Analysis of the invariant function and plot of the anisotropic invariant map show that 1D anisotropy prevails in the initial and lee sections of the dune under the action of downward seepage. Downward seepage increases mass and momentum exchange near the bed zone of these sections, causing a significant increase in the contribution and strength of turbulent intensities in the streamwise direction. Additionally, comparative studies employing octant analysis of bursting events under seepage and no-seepage conditions demonstrate that, at the initial and lee side sections of the dune, the probability of occurrences of ejection and sweep events increases with an increase in the seepage percentage. The present investigation can form a basis for understanding the effects of downward seepage on flows over bedforms, which has not been, to our best knowledge, taken into account in the previous literature and may therefore facilitate more accurate prediction of the rate of sediment motion during the migration of bedforms in an alluvial stream.

Hydraulic simulation models offer unlimited opportunities for improving the performance of irrigation canal systems by studying the flow behavior in a large and complex canal network under a variety of design and management scenarios. This paper presents an inner boundary in the junction-point water stage prediction and correction method, which deals with abrupt section change and the gates. To reduce the number of global iterations in the correction step, an acceleration method for local updates is also proposed. The results show that the proposed inner boundary satisfies the C Property and consistency, which can deal with hydrostatic conditions and dam-break junctions. The simulations in the test canal system show that the proposed inner boundary can simulate the control gate action and the resulting hydraulic response process in each pool. The proposed acceleration method can effectively reduce the number of global iterations, but the acceleration effect can only be improved by about two times.