Flood reconstruction using botanical evidence in Rapentosa catchment, in Marathon, Greece.

Résumé

Botanical evidence has been used in the past  for flash flood analysis, especially when instrumental data were scarce. This work focuses on the use of such evidence as a tool to study flash flood phenomena in Rapentosa torrent, in Marathon, Greece. To this aim, impact scars induced during past flood events    on trees along the torrent  , were  considered water stage indicators and were used   to determine discharge magnitude of these flow episodes. Samples extracted from the scarred specimens with the aid  of an increment borer, were used to date these impacts wounds. 1-D h y-draulic  modeling  was  used  to  provide  a  reconstruction  of  the  highest-discharge event, while results were cross-examined with    historical damages to verify the out-come of the analysis. Analysis showed a total of 22 impact wounds along the torrent indicating discharge values between 17.1 m3/s and 84.9 m3/s during past flow episodes. Three flash flood events were identified in 1996, 1998 and 2001. Hydraulic modeling of the 2001 event, which presented the highest flow values, illustrated its extent    and water depth across    the  flood  plain, presenting good correlation with the available documentary evidence.