Natural flood risk management in urban rivers

A study of floodplain sedimentation on a recently restored floodplain is presented. This study uses a two-dimensional hydro-morphodynamic model for the prediction of flow and suspended sediment dynamics in the downstream section of Johnson Creek, the East Lents reach, where the bank of the river has been reconfigured to reconnect to a restored floodplain on a 0.28 km2 (28-ha) site. The event based simulation scenarios (10, 50, 100, and 500 year) are considered in this study. Simulation results showed that the restored floodplain attenuates the upstream flood peak by up to 25% at the downstream. Results also indicated that ~ 20-30% of sediment from the upstream flow is deposited on the East Lents floodplain, this sediment trapping process at the East Lents flood basin considerably reduces the overall sediment loading into the main Willamette River.