Analysis of return flows in a tank cascade system in Sri Lanka

In Sri Lanka, irrigation reservoirs (tanks) are usually connected sequentially and form cascades along the landscape. A study was carried out in the Anuradhapura District in the dry zone of Sri Lanka to understand the role of return flows in such tank cascade systems. The water balance of a tank cascade system was estimated using hydrological data collected over a one-year period. The system was extended about 25 km along a river composed of three small reservoirs having the command area of 31, 55, and 55 ha, respectively. In this system, about 46% of seepage water from tanks entered the paddy fields of the command area. The crop consumed part of the water and the rest returned to the downstream tank through the drainage canals. Percolation loss in the command areas was low (3.6 mm/day) since a considerable portion of the percolation returned to the downstream tank. These results showed that return flows, which are generally disregarded in the water budget, contributed considerably to the water supply of the tank cascade system.     

Maintenance Management Process

A case study from Maharashtra comparing maintenance performance between two transferred minor canals on the one hand and two non-transferred minor canals on the other is presented. It is shown that the clear differences in maintenance performance are due not to differences in resources expended, but to differences in maintenance management processes. This study demonstrates that small differences in management process can lead to major differences in maintenance performance under severe resource constraints.     

Productivity of Rice—Wheat Cropping System in a Part of Indo-Gengetic Plain: A Spatial Analysis

Investigations were made to study the effect of unequal distribution of canal water in land and water productivity of the rice—wheat cropping system in terms of head—tail relationship in Bhakra Canal command, Haryana. Information on water supply, agronomic practices, crop yield, etc.,were collected from 216 farmers comprising 36 farmers each from the head, middle, and tail watercourses of two minors during year 2000–01. The unequal supply of canal water and presence of marginal quality groundwater creates large variations in the cropping pattern, irrigation application, and land and water productivity of the irrigation system. The groundwater of tail reaches, being saline in nature, was about 25% less productive as compared to head reaches. The unavailability of canal water in the tail reaches creates more dependency on groundwater. Due to its poor quality the crop production in the tail reaches was less by 10 to 20% in case of wheat, and 20 to 40% in case of rice, as compared to head reaches. Groundwater transfer from head to tail reaches and cultivation of low water requiring salt tolerant crops/varieties would be helpful in reducing the productivity gap and increasing the profitability of the farms in the region.     

Cumulative relative water supply: A methodology for assessing irrigation system performance

This paper discusses the usefulness and limitations of using the concept of Relative Water Supply (RWS) for evaluating the performance of irrigation systems, with special reference to systems irrigating rice. It then describes and demonstrates the use of a modification of RWS called Cumulative Relative Water Supply (CRWS), which can be used in conjunction with RWS. The advantage of CRWS is that it provides a measure of the cumulated RWS throughout a season, both in absolute terms at any given time, and in terms of the overall seasonal trend. It allows comparison of performance of an irrigation system or subsystem both to the target, and to other systems or subsystems. It can therefore be used both as an analytical tool by researchers, and as an operational tool by managers. The use of CRWS in conjunction with RWS is illustrated with examples from Sri Lanka.