Consequences of Koshi flood 2008 in terms of sedimentation characteristics and agricultural practices

Koshi flood of August 2008 in eastern lowlands of Nepal affected around 2.64 million people in India and Nepal, including 65,000 people and 700 ha fertile land in Nepal. It was calculated that 25% of the affected cultivated land of Shreepur, Haripur and western Kushaha villages in Sunsari district are still barren and remain filled with flood sediment of sizes from clay to sand even after 8 years. The issues of land change from fertile to barren because of flooding and characteristics of the sediments in terms of cultivation are the foci of this research. Field measurement and information from questionnaire survey showed that the depth of the flood sediment are highly variable in impacted zones. They are divided into central red, red, yellow and green zones as per the thickness of the sediments. The sediments from sieve analysis has also shown that the degree of fineness is greater towards the green zones and texture has shown function of distance : T = f (d). The average thickness varies from 0.10 m in green zone to 4.5 m in central red zone in new channel area of the flood. The crop yield is also 50–75% greater in green zones than in the other zones. Changing in cultivation practice from traditional crops to cash crops have increased income up to 200–300% in the aggraded land. Changing in cultivation practices and removing layer of flood sediment in shallow sedimentation area are the major overcomes against the flood sediments. The study concluded that the agricultural practices in aggraded land depends on sediment textures, composition, and thickness of the sediments.