It was hypothesized that the secondary salinization in the irrigated agricultural lands was largely caused due to externalities of irrigation system in the form of water logging, which in turn resulted from inefficiencies of the system in design, operation and maintenance.  It therefore stands to reason that prevention of the secondary salinization in irrigated agriculture be attempted through irrigation system improvements to maintain desirable environment across the entire system so that agricultural productivity is sustained.

 

Two major irrigation systems-the Bhakra Canal Command, which is a reservoir fed system and the Western Yamuna Canal  Command,  a run off the river fed system, together having a gross irrigation command area of about 2 million ha, were selected for diagnostic analysis.  It was established that extensive canal network with low irrigation intensity and poor conveyance, temporal and spatial mismatch between supply and demand, volumetric inequity in supply across the network   and large unit command areas were the major drawbacks that contributed to water losses and inefficiency. These problems were considered amenable to solution by introducing intra-seasonal modification in canal water delivery schedules, revisions in water allocations, provision of auxiliary storage at water course outlets and rationalization in unit command area size. To achieve this end, procedures for designing the required interventions were developed and tested and a decision support model for integrated water management at command area/sub-basin level was put in place.

Modification in canal water delivery schedule: A simulation model considering crop-water plant relationship, nature of soil, climatic conditions and water availability in the system at different locations, was developed for designing water delivery scheduling alternatives and applied. The results of application showed that it save 18 % of water without scarifying crop yields. The water that is saved through intervention was sufficient to irrigate10000ha of additional land which is cultivated under rainfed conditions.

Auxiliary storage at water course head:  Provision of auxiliary storage is an structural intervention that helps in temporary storage of water at water course head for use during the interval between two fixed frequency long duration delivery schedules. The utility of auxiliary storage as a means of increasing irrigation efficiency and productivity by minimizing the mismatch between supply and demand has been advocated and procedure to design the storage reservoir has been developed. Application of the intervention in Bhakra system is found to increase yield of wheat crop by 20 %. Auxiliary storage scheme has been found useful for introduction of micro-irrigation and is being executed in Indira Gandhi Canal Project in salinity prone area and has become big success. This concept holds promise for more than 2000 water courses covering an area of 1.2 million ha in saline zone. A 20 % increase in water productivity translates to 250,000 tons of additional food grains from the same water supply.

 

Rationalization of unit command area (UCA) size:  Farm land irrigated by a single water course is called unit command area and in rotational irrigation system down below the unit command area outlet, the subdivision of flow stops and subdivision (allocation) of time begins. The water flow rate assigned to the UCA depends upon its size and it has significant effect on equity and efficiency of water delivery. A model incorporating the concept of equity, efficiency and productivity has been developed for deciding optimum size of UCA and validated with data from Bhakra canal system. The suggested procedure would very useful in new irrigation project and also in the older ones where rehabilitation of the system was taking place.

 

Design of optimal mix of efficiency improving structural interventions:  Structural improvements in the irrigation system have benefits in the form higher efficiencies and the costs attached with them.  A decision support model to decide the optimal mix of technological interventions in irrigation system and their impact behavior has been developed and applied .The model outputs enabled specifying priorities for implementing best management practices to minimize annual rise in ground water table which causes secondary salinization. It was discovered that improvement in uniformity of water application through precision leveling was the most effective intervention, followed by intervention of micro irrigation and water course lining The results were field tested and it was found that irrigation intensity increased in the order of 20 to 35 % depending upon the initial status of the irrigation system.