GIS Based Efficient Distribution System for a Command

Abstract

Conjunctive management of water resources in irrigation systems requires multidisciplinary data pertaining to hydrological, hydro-geological, hydro-meteorological, soil, agronomic, and cropping pattern parameters in command areas. Further, a model is required that can integrate all the available information to evaluate the system operation and provide an integrated picture of the total system. Computers now make possible the use of larger data sets, more sophisticated analytical techniques and a variety of graphical means for presenting analysis results. While the demands for water by all the sectors (municipal, industrial, irrigation, hydropower etc.) are rising, investments for development of additional water resources are limited. This requires more efficient and rationale utilization of the available resources based on scientific principles. The realization of this objective in the irrigation sector requires a formal framework for water resources decision-making that enables spatial assessment of water supplies and demands in real-time and a balancing of the two to meet specified objectives. A GIS based procedure has been developed in the present study for conjunctive operation of the canal system. The model utilizes real-time data and multi-disciplinary spatial and attribute data in a canal irrigation system and can help the operator in decision-making process. The model uses the real-time irrigation demands in the command area (calculated by another model) and calculates the total flow requirements at each minor, distributory, and branch in a canal system after accounting for the water application efficiency, field channel efficiency, seepage losses, and canal capacity and water availability constraints. In addition, the model uses the information of groundwater depth in the irrigation system for finding the optimum canal-run configuration during each week. The model aims at utilizing the available canal water to the maximum extent provided that groundwater conditions in the area permit. In case of shortage of surface water, the demands of a minor/distributory with least water table depth are met from groundwater. Through iterative simulation of canal operation, the model finds a canal-run configuration that provides higher effective utilization of canal water, relatively higher canal seepage in the areas of deeper groundwater and requires least energy for pumping groundwater. In the development of this procedure, it is inherently assumed that it is always economical to utilize the surface water as compared to the groundwater provided that surface water is available. A computer program has been written for the allocation model and applied to the Lakhaoti command area under the Madhya Ganga Canal system. Data requirement of the model is quite high. Detailed database has been developed for the Lakhaoti command. Layout of canal system up to the minor level has been delineated using the PAN sensor data of IRS- 1C satellite. Minor-wise command area has been digitized. The location of groundwater wells and the groundwater depths in various wells in the year 1998-99 have been collected from field offices and groundwater surfaces have been generated in the GIS system (ILWIS). Characteristics of different canal segments have also been collected from the field offices of the Madhya Ganga Canal system. The operation of canal system is based on the irrigation demands (as worked out by another model), canal water availability and the groundwater depth in any week. Major advantages of the model are that it operates the system for the actual cropping pattern and uses real-time information about spatially distributed irrigation demands and groundwater depths. It considers different characteristics of the canal segments and utilizes the information of different irrigation practices in different parts of the command area rather than assuming lumped values. Further, the model uses least number of assumptions in terms of canal seepage, recharge because of rainfall and irrigation, income and expenditure on various crops, and cost of providing surface and groundwater etc. The approach suggests the operation plan for each week. The aim is to satisfy the irrigation demands in the command area with least cost of pumping. To approach also tries to ensure groundwater stabilization by curtailing canal water supply in the water logged area, pumping groundwater in the shallow water table area and using canal water in deeper groundwater area. One major limitation of the model is extensive database requirement. The model requires digitization of Sajra maps for the whole canal system. Further, the approach requires the determination of actual cropping pattern for the command area before the start of the season. The approach also requires a network of well-distributed groundwater observation wells and collection of groundwater level data from the observation wells at weekly/monthly time step. However, once the database is developed, the model can show simulation analysis for different scenarios of canal water availability in the form of maps and tables. The model can be used to design or alter the system configuration and different scenarios of canal capacities and canal system layout, and area actually irrigated by them can be evaluated.