In view of the increasing flood and sediment disasters from the streams in Siwalik region of Nepal, it is important to examine both the historical changes and present geomorphological characteristics of the stream systems. With the objective of analyzing stream course change characteristics and identifying governing factors, we carried out the study in three streams of eastern Siwalik region using sequential aerial photographs covering period from 1964 to 2003. Overlay of rectified photographs indicates that forest cover in the headwaters of the streams remained more or less unaffected over the recent times. The stream reaches are divided into four geomorphologic units: hill, terrace, floodplain and alluvial fan. Overlay of stream planform indicates that there is distinct variation in their development patterns in different stream reaches. It is revealed that the stream channels in the terrace reach are characterized by gradual widening. Similarly in the floodplain reach, gradual widening and course shifting are predominant. The streams are characterized by quick generation of runoff flow and high sediment content, which could be responsible for the frequent course changes. Application of structural countermeasures against bank erosion in terrace and floodplain area and conservation works such as gully control in the Hills are suggested.

Key wordsFLanduse change, stream course, bank erosion, countermeasures, aerial photographs