A GIS based study on bank erosion by the river Brahmaputra around Kaziranga National Park, Assam, India

Abstract. The Kaziranga National Park is a forest-edged riverine grassland inhabited by the world's largest population of one-horned rhinoceroses, as well as a wide diversity of animals. The park is situated on the southern bank of the Brahmaputra River at the foot of the Mikir Hills. National Highway 37 forms the southern boundary and the northern boundary is the river Brahmaputra and covers an area of about 430 km². The Brahmaputra River flows by Kaziranga National Park in a braided course for about 53 km. Sequential changes in the position of banklines of the river due to consistent bank erosion have been studied from Survey of India topographic maps of 1912–1916 and 1972, satellite IRS LISS III images from 1998 to 2008 using GIS. Study of bank line shift due to the bank erosion around Kaziranga has been carried out for the periods 1912–1916 to 1972, 1972 to 1998 and 1998 to 2008. The amounts of the bank area lost due to erosion and gained due to sediment deposition are estimated separately. The total area eroded during 1912–1916 to 1972 was more (84.87 km²) as compared to accretion due to sediment deposition (24.49 km²), the total area eroded was also more in 1972–1998 (44.769 km²) as compared to accretion (29.47 km²) and the total area eroded was again more in 1998–2008 (20.41 km²) as compared to accretion (7.89 km²). The rates of erosion during 1912–1916 to 1970, 1970 to 1998, and 1998 to 2008 were 1.46, 1.59 and 1.021 km² per year, respectively. During the entire period (1912–1916 to 2008) of study the erosion on the whole was 150.04 km² and overall accretion was 61.86 km² resulting in a loss of 88.188 km² area of the park. The maximum amounts of shift of the bankline during 1912–1916 to 1970, 1970 to 1998, and 1998 to 2008 were 4.58 km, 3.36 km, and 1.92 km, respectively, which amount to the rates of shift as 0.078, 0.12 and 0.096 km per year, respectively. A lineament and a few faults have controlled the trend of the course of the Brahmaputra around Kaziranga area. The main cause of erosion of the Brahmaputra is the loose non-cohesive sediments of the bank throughout the park. The braided channel of the river strikes the bank directly and undermines the silty bank causing overhanging blocks to be carried away easily by the river current. In future deposition is likely to be more in upstream or eastern part of Kaziranga and erosion in middle part of Kaziranga national park area due to the river Brahmaputra. Antierosion measures have been adopted only in a few places to check bank erosion at Kaziranga.