SPATIALLY DISTRIBUTED SIMULATION OF AN IRRIGATION SYSTEM

Abstract

Success of an irrigation system depends on efficient water management. The National Water Policy of India (revised in April 2002) states, "Certain problems and weaknesses in planning and implementation have affected a large number of water resources projects all over the country. Problems of water logging and soil salinity have emerged in some irrigation commands. Complex issues of equity and social justice in regard to water distribution are required to be addressed. The development and over-exploitation of groundwater resources in certain parts of the country have raised the concern and need for judicious and scientific resource management and conservation." Efforts to improve agricultural practice by making more efficient use of available water resources require mathematical models to simulate the dynamics of water distribution in an irrigation system. A number of computer-based models have been reported in the literature (such as SIMIS, CAMSIS, INCA, OMIS etc.) to help irrigation manager in real-time operation of a canal system. Such models analyze the system operation in terms of water demands and supply and optimize the water allocation to meet some performance-based criteria/objectives. Irrigation command areas may exhibit marked spatial heterogeneity in terms of cropping pattern, physiographic characteristics, irrigation practices, water availability and utilization etc. Groundwater availability in an irrigation command varies spatially as well as temporally depending on the depth of groundwater table below the land surface, and groundwater extraction facilities. Often, gross simplifying assumptions, such as areal average cropping pattern, uniform physiographic and agro-climatic characteristics and average groundwater availability etc. are made in planning and operation of canal irrigation projects. This may lead to glaring discrepancies with ground situation resulting in inefficient utilisation of water resources. Available literature does not indicate the existence of a spatially distributed simulation model that can integrate various processes of irrigation management from micro-scale (field level) to macro-scale (overall command) and provide a comprehensive analysis.