Journal of Watershed Management Research

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     The occurrence of a great number of floods in rivers on the one hand, and industrial, commercial and social activities’ accumulation, just near the rivers, on the other hand, reveal the obligation of applying appropriate flood management strategies (before, during and after the flood). The role and importance of employing Flood management strategies on flood damage reduction could be observed clearly, at the Nekaroud River over flow which had occurred in 1999. In this year two floods occurred in June and August in Nekarood’s basin, respectively. The first one destroyed the city center’s bridge and obstructed the river which finally caused back water at the second flood which was the reason of extremely major damage in the city of Neka. In this article, the effects of city main bridge destruction on exacerbation of flood damage, in August 1999, have been modeled using HEC-RAS software; therefore, the geometric characteristic of 25 river cross sections at the upstream of the bridge, Manning's roughness coefficient, flow type and the boundary conditions, were inputted. Besides, the model was calibrated using discharge-stage at the existing hygrometry station on the river. Then, the water surface profile were calculated in two different conditions first normal river condition and 70 percent blockage at the bridge section, then, compared with measured water stage of the flood occurred in August. The results show that the amount of the second flood discharge was not the original factor which led to such extremely flood damage, but it was the bridge blockage, as a consequence of the second flood. Eventually, a flood with 970 CMS caused severe damage equal to a flood with 2450 CMS and if the bridge spans were cleaned after the first flood, no back water and such damage would not be happened at the second flood.   
 

Keywords: Nekarood River, Flood, Flood Management, HEC-RAS

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