Dynamic river morphology due to land use change and erosion mitigation measures in a degrading catchment in the Siwalik Hills, Nepal

ABSTRACT

This paper presents findings of an evaluation study that focused on the changes in land use and stream planform and various morphological changes in a small degraded catchment of the Siwalik Hills in Nepal. The study was based on a spatial analysis of historical aerial photographs (1964–2010) and several field measurements and observations (1998–2012). Analysis of historical aerial photographs indicated that noticeable deforestation occurred during the period between 1964 and 2003 as a result of expansion of agricultural land. Several types of morphological changes were observed from both aerial photographs and field observation. The stream channels were characterized by active bank erosion with an increase in width, particularly from 1964 to 2003. There was a noticeable sediment accumulation in the lower reach, while a combination of bank erosion, channel widening and lateral movement of the active channel was observed in the middle reach. A strong link between the historical changes in land use and changes in stream channel morphology was found. It is suggested that appropriate conservation measures should be implemented to control sediment supply from the upper reaches where key sediment sources such as landslides and gullies are located.

Keywords:

• Land use change
• channel change
• bank erosion
• mitigation
• Siwalik Hills

Acknowledgements

We thank the two anonymous reviewers for their comments and constructive suggestions.

Funding

We acknowledge the help and support from the Department of Water Induced Disaster Prevention (DWIDP), Kathmandu, throughout the project. We thank local people of Deuri, Udayapur, for their help and support during field monitoring and evaluation work. Also, the help of Prof Naoto Koiwa and Mio Kasai of Hirosaki University, Japan, and Shanmukhesh Amatya of DWIDP during the field survey of December 2012 is gratefully acknowledged. Financial assistance and resources were provided by the James Hutton Institute during the preparation of this paper.