Performance of subsurface drains for reclaiming waterlogged saline lands under rolling topography in Tungabhadra irrigation project in India

With the introduction of irrigation in areas with rolling topography, low-lying areas are prone to water logging and soil salinization. The problems also occurred in the valley bottoms of the Tungabhadra Irrigation Project (TBP). Subsurface drainage was applied to reclaim the waterlogged saline land in an area of 62 ha (1 ha = 10,000 m2). The drainage system consisted of three pipe drains laid parallel to the valley brook at a spacing of 150 m. The monitoring and evaluation of the system revealed that the water table was lowered; electrical conductivity (EC) of the soil decreased and crop yield and cropping intensity increased in the drained area. Hence, the intervention effectively reclaimed the land, even though the spacing was unusually wide. The cultivation of submerged lowland rice aided in the leaching of salts within a period of one year. Originally the drains were thought to function as interceptor drains and their main effect would stem from intercepting the underground seepage water from the canals in the upland. On the other hand, while assessing the performance of the system, it was observed that drainage discharge and EC of the drainage effluent in all three drains were of the same magnitude. It emerges, therefore, that the system was rather working as a normal subsurface drainage system than as an interceptor system.