Delimitation of Channel Migration Zones in the Rapti River Basin, Middle Ganga Plains

Abstract

Channel migration is an important geomorphological process in the floodplain area.
The rapid shifting of rivers has not only complicated the flood problems but also undermined
engineering structures and pose constant threat to public infrastructure. In these areas risk
minimization through channel migration zoning forms the core of river management
programme. The present study on river Rapti analysed historical information and field data
to interpret past and present channel conditions in order to predict future channel behaviour
and areas at risk of channel movements. River Rapti is a foothill-fed river originating from
the Siwalik hill areas of Nepal and draining the interfan areas between the Gandak and the
Ghaghra. The river is known for its frequent channel movement. Several studies based on
conventional and historical data confirmed its unpredictable channel behavior. This study
delineated boundary of the channel migration zone (CMZ) with the help of geospatial data
ranging a period of over 70 years and limited field survey. The CMZ is the cumulating
product of the Historical Migration Zone, the Avulsion Hazard Zone, the Erosion Hazard Area
and the Disconnected Migration Area. The river Rapti being a foothill-fed river exhibit spatial
variations in channel migration throughout its course. Several broad patches of CMZ are
observed along its lower course where there is concentration of human settlements, economic
activities and infrastructure. The study found that constant channel migration is undermining
various engineering structures, eroding valuable and productive agricultural land and enhancing
vulnerability of the floodplain dwellers. The study further recommended that site suitability
analysis should be undertaken prior to construction of any engineering structures including
public infrastructure