The Response of Fluvial Systems to Large Flood Events

In the summer of 2001, an intense thunderstorm in southeastern Caspian Sea triggered a catastrophic flood in the Madarsoo basin . Use of methods including high-resolution aerial photographs and satellite images interpretation, multi-date mapping, hydraulic calculations and field observations made possible the documentation of the geomorphic impacts on the Madarsoo River and its tributaries. Geomorphologic effects of this catastrophic flooding included: trees up to 2m in diameter were scoured from the main river channels and locally as much as 80% of trees crown cover was removed from riparian zones. The scour of trees exposed the underlying flood plain to macro turbulent scour, leading to extensive removed of flood plain sediments that had accumulated over centuries. Other hydro-geomorphic impacts of this flood have been drainage network modifications create new alluvial fans, new meandering pattern and gully development that all of them have been documented by authors. Subsequent to the mentioned flood two other extreme floods also affected the basin in the August of 2002 and 2005. In addition to causing further landform modifications, It wiped out the infrastructure which was reconstructed posterior to 2001. All three floods were in the same conditions on the basis of their time, climatic and triggering characteristics. The peak flood was estimated 700m3s-1 in August 2002, and also 1060 m3s-1 August 2005. the occurrences of the two above mentioned catastrophic floods and related processes were result of triggering variables, forming a new dynamic environments by the main event (August 2001 flood), Which prolongs the required time for recovery of stream channels. Geomorphic instabilities lead to consecutive Crises in this new environment. This Condition accelerates geomorphic hazards in combination with the effects of recent climatic