Analysis of Synoptic Showery Rain falls Contributing to the Formation of Flood Within Rivers of Gilan Province

Ghodrati Alireza

Faculty Member of Gilan Agricultural and Natural Resources Research and Education Center, Gilan, Iran.

DOI : http://dx.doi.org/10.13005/bbra/2588

ABSTRACT: One of the most important factors leading to occurrence of We usually use flood is weather phenomena, such as Severe cloudbursts and accomplishment of the  It should be removed  .Climate study and identification of weather phenomena, especially the cloudbursts have an important role in forecasting the floods and making flood warning plans.  Therefore, this research has been conducted in order for Climate analysis of the cloudbursts leading to flood in west of Gilan Province. For this purpose, statistics of floods and local cloud bursts related to each flood in west region of Guilin were identified and drawn out since 2001-2011. Accordingly, during this period of time 13 floods and local clod bursts were identified, then in the next stage, serological isobar plans for sea level and 500 1000 hectopascal  geopotential for pre –rainfall days and rainfall day received from NOAA diagram and was observed using isometropia analysis method And each one was analyzed using the GrADS software for mapping required at ground level .Curbing and reducing of flood damages has a special status in exhaustive management of   watershed areas. Thus, precise identification of flood-prone regions on field level is extremely important and significant, since we can reduce flood-proneness level of the field using proper watershed procedures, either constructional or non-constructional, or a combination of both. In order to determine the hydrograph of the runoff resulting from precipitation under the fields, HEC- HMS mathematical model, in which precipitation’s change into runoff is done, based on hydrological methods, has been utilized. In the present research, the calibration and validation results of model HEC- HMS indicated that in case of presence of dry condition, initial damages coefficient in this field would be equal to 15.0 , A coefficient for calculating the concentration time under the fields based on  relation in Tamar field would be 4.0, and  B coefficient for all subfields would be equal to 3.0 and the ratio of saving coefficient to concentration coefficient in Tamar field would be 4.0 , based on which we can see that the observed and simulated hydrograph has high correlation.  After calibrating and validating the model, prioritization of the subfields in terms of their participation in output flood (flood-proneness analysis) was examined. Based on flood-proneness studies in Tamar field we can conclude that upper subfields have had the greatest effect on flood-proneness level with regard to the selected floods in the field.

KEYWORDS: Rainfall and Runoff; Flood; Pressure System

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