1. Sedimentation in Koshi: a central problem!
Contributions from:
Rajiv Sinha, Kanchan Mishra and Shobhit Singh
IIT Kanpur
Santosh Nepal, Kabir Uddin ICIMOD
Basanta Adhikari
Sichuan University
Liu Linshan
IGNSRR, China
Biraj Singh Thapa
Kathmandu University
Tectonics
Precipitation
Runoff
Deforestation
Hinterland characteristics +
Sediment Flux
Human
Interventions + +
River dynamics + + +
Bank instability
and Erosion
Aggradation/
degradation
Drainage congestion
and Waterlogging + + +
Flooding

2. Sedimentation: Unresolved issues
Birpur
81 Mt/yr
Chatara
101 Mt/yr
Dolaghat
30 Mt/yr
Mulghat
16 Mt/yr
Busti
10 Mt/yr
Indrawati / Bhote Koshi
Tama Koshi
Arun
Sun Koshi
Tamor
Baltara
43 Mt/yr
Hayaghat
7 Mt/yr
Jhanjharpur
8 Mt/yr
Sapta Koshi
Kamla-Balan
Baghmati
A First Order Sediment Budget for the Koshi
Why?
Lack of process-understanding on sediment production, sub basin-scale data on hydrology and sediment
Where?
No maps of the hotspots of siltation to prioritize the action
How much?
No estimates of the silt accumulated in the channel
What to do?
No assessment of commercial uses of silt and no mapping of stakeholders
=> Need a comprehensive Silt management Plan

3. What do we know so far?
Sapta Kosi
Kamla
Baghmati
Likhu Khola
Arun
Tama Kosi
Tamor
Indrawati
Bhote Kosi
Dudh Kosi
Balan
Geomorphic processes of sediment production and transport
Basin-scale LULC changes and impact on ecosystem services
Basin scale hydrology and sediment transport characteristics
First order sediment budget and sediment volumes
Impact of sedimentation on floods, river dynamics and hydropower facilities
Basic understanding of sediment dynamics – sediment connectivity, use of seismic methods
Higher Himalaya
Interfan
Mountain front
Megafan

4. Knowledge gaps
What is the basin-scale upstream-downstream linkages of LULC change, erosion, and sediment flux in terms of river morphodynamics and hazards?
What is the spatial variability at sub-basin scale in terms of sediment flux, LULC change, sediment connectivity?
What are the drivers, natural vs anthropogenic, of LULC changes at sub-basin scale and their impacts on erosion?
How is sediment connectivity related to landslides zones and how does this affect the sediment mobilization into the river?
How do we integrate sediment management in designing hydropower facilities through innovations and technology?
What are the quantifiable impacts of the existing interventions and possible impacts of future interventions?

5. LULC change and sediment transfer
Engineering challenges of hydraulic interventions and hydropower development
River morphodynamics and sediment dynamics u/s and d/s of interventions
Maintenance of hydraulic and associated structures e.g. embankment health monitoring
Erosion of turbines and other associated components
Reservoir siltation
Drivers – natural vs anthropogenic?
Impact on ecosystem services?
2 MW Chinese Runner, Nepal
Need innovations in design of interventions for sediment handling
Need to address ecological concerns - e-flows, ecological disconnectivity
Guide vane
8MW*3 Bhilaganga III HEP, India

6. Sediment dynamics and hazards
‘Hotspots’ of siltation and flood risk
Sediment connectivity – defines potential of sediment pathway and delivery
Catchment
Outlet
Pipra
Hillslope-channel
Connectivity
Joginia (1991)
Dalwa (1963)
Kunauli (1967)
Bhatania (1971)
Navhatta (1984)
Jamalpur (1968)
Ghonghepur (1987)
Kusaha (2008)
Kusaha
Koshi barrage
Superelevated
River!
Channel-outlet
connectivity
Catchment
Outlet
Integration with landslide distribution data
Identify critical areas for immediate attention
Design mitigation measures based on process-based understanding

7. Stakeholder engagement
Way Forward
Managing
Koshi Basin
Multiple expertise available in the DRR hub can be utilized to take up solution-oriented studies
Given the enormity of the problem and associated hazards, a transboundary cooperation is necessary for sustainable management of sediments and DRR
Data server at ICIMOD
Feedback and
Feedback and
Project partners
User groups
Interactions
Interactions
Solution-oriented research
Hydrology-Ecology Reln.
Sediment
flux
River dynamics
Linkage with other groups
D/s impacts
Flood risk, GLOFs
Landslide
Sediment management Framework
Stakeholder engagement
Role of Technology
Business plan for Silt utilization