The effect of river floods on the morphology of small rivermouths in the southeastern Mediterranean

摘要

River mouths on the Israeli Mediterranean coast exhibit a highly dynamic mor-phology. They deflect hundreds of meters along the shoreline and experience periodic open-ing and closure. They are characterized by low discharges, which occur mostly during winter floods, and high concentrations of wastewater flow. This study examines the effect of floods on the dynamic morphology of seven of these river mouths between 1918 and 2005. The methodology is based on GIS techniques and utilizes over 300 aerial photographs from which detailed geomorphologic mapping of river mouths and nearby geomorphologic elements was performed. River discharge records were incorporated into a database, permitting analysis of the effect of floods on the morphology of the river mouths. River floods were found to have a short-term morphological effect on the mouths, mostly through channel cut-off and diversion. Flood morphology, identifiable in aerial photographs, included wide channels and large inun-dated areas adjacent to the channels. On rare occasions, floods caused the breaching of second channels flowing to the sea simultaneously. Based on their adjacent topography, two types of mouths were recognized, each responding differently to river floods. In funnel topography mouths, flood morphology almost always displayed straight channels. In barrier-deflected mouths the response to floods is more complex. In some flood observations, the channel was diverted away from its barrier deflected "semi-permanent" normal position along dune toe, but was deflected either north or south. In other observations, even large magnitude floods were unable to divert these semi-permanent channels. Well-established semi-permanent chan-nels and low sinuosity values are intrinsic morphological conditions that can prevent straight flow to the sea even in the event of large floods.