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Top1. Introduction
Irrigation is the process of providing water to the crops through dams and canals. Diversion dams divert water from river/ water source into an artificial water canal which is used for irrigation. Dam is provided with a number of water regulating gates that are used to control the water discharge from it. Gates are also used to divert water into irrigation canals during flood emergencies to minimize the adverse impact of flood. Simple water level control can be achieved through manually operated structures, like flap gates without the need of any electronic control. However, electronic control provides added benefits of remote control, alarm, warning on PAS (Person Address System) and data storage, which can be integrated into maintenance and business system (billing, maintenance, upgradation, future planning, etc.). The main objective of irrigation automation is to provide at all times optimum quantities of water to the farmers balancing the water delivery and water availability.
The level of control depends on the accuracy of the water flow rate, usually defined as the outlet water level required on these irrigation channels. If multiple gates are used to control flow through a single canal/channel, each gate is operated on its bi-state level (either ON or OFF, that is either fully open or fully closed) and the number of gates opened defines the outlet water flow. Whereas if a single gate is used to operate on each channel, the gate should be controlled along its operating range of 0% to 100%, representing fully closed to fully opened state. Either way, control/automation of dam gates is the function of the in-stream water level and required water discharge level. Selection of the control system for a given application will depend on cost-benefit analysis. The cost of automation is related to the scale of irrigation project and technology used. Embedded solution is more cost-effective than PLC based system, latter providing industry-standard control features. This includes after-sales support, diagnostic, ease of upgradation and integration with other systems, ready compatibility with field devices, ease of field wiring, and the cost of commissioning. Major irrigation projects cost huge finance to be established and maintained, where cost of PLC-based automation, though high, would be just a fraction of the total project budget.
Typical benefits of automation of irrigation dams are stated below (Wahlin and Zimbelman, 2014):
Requirement oriented means providing water as per farmers’ requirements. This enables the farmers to have a capacity to enhance on-farm irrigation system like drip and sprinkler irrigation which requires constant water delivery. Automation allows farmers to adapt to market demands by choosing the required crops. Demand-based supply eliminates the farmers to maintain water storage, pits, reducing land wastage where again crops can be grown.
Traditional irrigation diverts water from a source at a high flow rate through the channels which reenter the river downstream. So, an improved control system helps to maintain water inlet from river at demand rate, maintaining river flow and river ecosystem.
Real-time information provides actual water discharge required and flow is controlled to reduce end losses. Overflow can be recaptured and recycled back to the source.
Real-time data helps operators to manage operation easily. The visual/ audio feedback aids operators to understand the conditions of water operation. The data recorded can provide a reference for future planning, risk assessment, and management like flood and drought.
Water level and discharge can be controlled within a range using an automated control system.
Data recorded provides accountability for operators to maintain water inflow from the river to the dam and also discharge to different channels.