Geomorphological effects of catastrophic flooding on a small subtropical Estuary

摘要: The Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from mouth. subtropical climatic regime causes seasonal flooding, geomorphological effects which are increased by a steep river gradient. A 120-150 year flood event during September 1987, with an estimated peak discharge 10800 cumecs, resulted in erosion 1.86 × 106 m3 sediment estuary. normal high tide volume estuary (0.35 m3) to 1.85 after flood. post-flood intertidal (tidal prism) was 0.43 compared 0.19 before event. The nature and extent controlled composition banks bed material. Gravel sand substrates were preferentially eroded cohesive bank materials undercut sections Mud fine deposited overbank areas when waned lag coarse gravel produced bed. Approximately 46 per cent bedload supplied since 1917 retained until 1987 remainder transported through system into Indian Ocean. Results show that catastrophic floods play important role sedimentation small estuaries.