Investigation of the Effect of Operational Errors on the Performance Uncertainty of Irrigation Networks in Arranged Delivery

Introduction:

To improve the water productivity in irrigation canals application of more flexible water delivery is suggested by many researchers. To this end substitution of arranged delivery methods for rotational delivery is recommended. In the arranged delivery system the spatial and temporal variations of numerous requests increase the operation complexity. Such complexity increases the probability of structural adjustment errors and operational uncertainty. This might adversely affect the performance improvement of irrigation canals. Therefore in arranged delivery, the impact of operational errors on the performance uncertainty of irrigation canals should be investigated.



Objective:

The objective of this research is to consider the operational errors of control structures including check structures and turnouts and analyze their impact on the performance uncertainty of the canal.



Materials and methods:

In this research, the Monte Carlo simulation method is used to assess the uncertainty. The steps followed in this research are, determining the variables, creating random numbers for structures’ adjustment, defining and simulating the scenarios, and evaluating the results. For this purpose, in one canal of the Aghili irrigation network in the province of Khoozestan in Iran, two increasing and decreasing request scenarios are defined. In each scenario, operational errors of different selected structures are defined. The options include the application of errors on one check structure, a combination of one check structure and one outlet, and multiple structures. Using the Monte Carlo simulation method for different scenarios, random numbers for adjustment of the selected structures were generated for each option and simulated using the ICSS hydrodynamic model. The analyzed outputs are delivery flow rate, delivery adequacy, efficiency, stability, and parameters of water depth control errors. The probability density functions of the outputs are determined and their uncertainty level associated with different levels of structure adjustment errors are calculated. The uncertainty of outputs is calculated for the operational errors of 38 to 95 %.



Results and discussion:

A summary of the most important results could be stated as follows. Output indicators mostly fit with Beta and Normal probability distribution functions. The obtained uncertainty band of flow delivery for the increasing scenario is 38 to 95%, and for the decreasing scenario is 33 to 85%. The uncertainty range of the outputs for increasing scenarios is more than that for decreasing scenarios. By increasing the number of structures that encounter operational error, the uncertainty of almost all outputs has increased. The highest increment of 12% was seen in the stability index for the increasing scenario and an 8% uncertainty band increase in the depth index for the decreasing scenario. For increasing scenarios, delivery discharge with an uncertainty band of 38 to 95% is the most sensitive parameter. For decreasing scenarios, the depth control parameter with an uncertainty band of 36 to 82% is more sensitive compared to delivery flow.



Conclusion:

The results indicated that by increasing the number of structures that operate with error, the uncertainty of all output indicators will be increased. Therefore, for irrigation canals with a higher number of control structures, a more accurate operation should be applied. The uncertainty of the output indicators for increasing scenarios is higher than that of decreasing scenarios, which reflects different hydraulic behaviors and responses to operational errors. So accurate operation for increasing scenarios is more important than the decreasing ones. For increasing scenarios, delivered discharge and delivery adequacy and efficiency are the most sensitive parameters to operational errors. For decreasing scenarios, depth control parameters, are more sensitive compared to delivery discharge. Therefore, for increasing scenarios the delivery discharge, and for decreasing scenarios, the water depth are more important parameters to be controlled.