Evaluating diversion channels for mitigating super-elevation on the middle Kosi River using Delft 3D

The natural transfer of sediment from channel to floodplain has been disrupted on many rivers by levees and dams. One unfortunate consequence of this disruption is the accumulation of sediment on riverbeds. In extreme cases, this accumulation can lead to rivers flowing above their floodplain. Super-elevated riverbeds increase the chance of levee breaches, cause waterlogging outside levees, and heighten the potential danger of a breach. This is a concern along China’s Yellow River, Pakistan’s Indus, India’s Kosi, and the Missouri River in the United States. In lieu of continual dredging or other costly sediment management, we investigated diversion channels to reduce sediment accumulation on the riverbed of the Kosi River in Bihar, India where flooding claims an average of 238 lives each year. Sediment diversion channels use the power of the river to redirect sediment to the floodplain or storage areas outside river levees. This technology is currently being implemented on the lower Mississippi river to replenish the Louisiana delta. To investigate the efficacy of sediment diversion channels for removal of riverbed sediment, we used Delft3D to create a schematic model of fluid and sediment flow in a reach of the Kosi. Results indicate that channel geometry, threshold elevation, and channel location all play a role in determining how long a diversion channel will remain open, how much sediment it will capture and convey, and what upstream and downstream effects it may cause.