Evaluation of economic loss due to irrigation system inefficiency: a case study of nepal gandak west canal irrigation system

The main objective of this study is to estimate the total economic loss due to inefficient supply of irrigation water in the command area of Nepal Gandak West Canal Irrigation System. Several approaches have been used for this purpose. The optimal level of water needed for different crops is calculated using the methods suggested by the PDSP manual using Penman-Montheith Equation based on the available hydro-metrological data and field assessment of crop calendar. Crop yields in the developing world are consistently higher in irrigated areas than in the rainfed areas. Nepal Gandak West Canal Irrigation System (NGWCIS), under AMIS also have the similar problem; it has some uplands and also poor access to irrigation during dry season. Within the command area, there are several shallow tube wells are in operation, which increased the cost of irrigation even already have canal irrigation system.
The water available is calculated based on the sediment assessment and evaluation of reduced canal capacity based on the method proposed by Khazratov (2020). The timeliness of supply and quantity of water is crucial, which motivated the farmers to explore the alternate water sources. The data on water use, cropping pattern, agricultural system, and issues with water availability, inventory on alternate water use and associated cost, and types of energy uses for alternate water sources were collected through focus group discussion, observation checklist, and key informant interview. The command area of the system is characterized by high agriculture area with very low sign of urbanization, few industrial expansions and most farmers owing a shallow tube well as a supplementary irrigation source due to unreliability of operation of the system. The irrigation system is also characterized by high silt entry and deposition consequently reducing the bulk water delivery of the system.
Farmers are using their own diesel pump to irrigate their farm land from shallow tube well within the command area. Mostly Farmers are depending on canal (surface) water, rainwater, and groundwater for their irrigation as per requirement. The economic assessment of the tubewells was carried out based on the deficit of water, operation hour of pump and total cost associated with the operation and this is considered to be the total economic loss due to poor irrigation system. The total estimated economic loss for this was calculated to be 406 thousands USD which should be addressed through proper rehabilitation and operation and maintenance techniques. The requirement of each crop with seasonal variation is entirely attributed to the variation in their growth from seedling to maturity, potential evapotranspiration attributed by the climatic variation and effective rainfall. The highest value is observed in August where the command area is mostly covered by Paddy while the lowest area is observed in June where most of the area is fallow with very small area covered by Maize.
The effect of the operation schedule which also includes the maintenance period doesn’t ensure the year-round irrigation system in the large irrigation systems and similarly poor sediment control mechanism continuously reduce the capacity of the canal which restrict the limited supply of water to the farmers. The realization of high productivity from the timely and sufficient irrigation facility encourages the farmers to search and install alternative irrigation facility and giving additional production cost to the farmers.