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Flood Hazard Zonation Using Hydraulic Model of HEC-RAS in GIS
M. Mohseni
Former Master of Sciences Student in Watershed Management,
University of Mazandaran, Sari, Iran.
K. Solaimani
Associated Professor,
Faculty of Natural Resources,
University of Mazandaran, POBox 737 Sari, Iran
solaimani2001@yahoo.co.uk
Abstract
Flood plain and area near to rivers, because of their special condition are suitable condition for social and economical activities and usually, they are affected by different flood hazards. However in these zones determination of flood zone and its height and also detecting properties of floods in different return periods is most important. So flood zonation is necessary for suitable development and main parameter for investigating of ecological and environmental effect. Interaction between some river hydrologic models and geographical information systems (GIS) cause some gains and methods, which are sensible to the planners. This study was carried out with the purpose of using hydraulic model of HEC-RAS with Arc View software to estimate the flood zone of 5-km distance on Neka River in northern part of Iran. In order to flood zonation for different periods of 2, 5, 10, 25, 50, 100 and 200 years at 1:1000 scale topography maps were used. The results can be concluded that combination of GIS and HEC-RAS model in this study is useful and efficient. Finally the flood zone of 25 years is predicted to be more dangerous than the other periods for the selected area.
INTRODUCTION
With increase in agricultural activities along rivers and concentration of population around submergible areas, the flood-induced damages are in increasing trend. The complete flood protection with installation of great flood control structures like flood dams are not justified due to its high cost. It is not environmentally, socially and economically an optimum idea either. For this reason, the flood zonztion can have a considerable role in flood management through logical utilization of weir gates and dam reservoirs. In this direction, different systems have been innovated in different countries of the world, but lack of equipment and tools and also high cost of installation are the limiting factors in Iran (3). Recently the flood return period has decreased in Neka Basin of northern Iran, so a suitable method of decreasing the flood-damages is required, by flood zonation. The overall aim of this study is to find out the efficiency of GIS to create the main inputs to simulate a comprehensive hydrological model. So that the main requirement of a hydrological model is the description of flow channel characteristics and land surface as input to watershed model. The flood zonation is in fact the development and perfection of the applied engineering hydrology and its aim is to obtain real time data of rainfall and river flow by short wave, radio and satellite network and using them in rainfall-runoff models to forecast and also zonation of floods in consecutive time and space intervals (4). The quality of flood forecasting systems depends mainly on the quality and the amount of basic collected data about hydrology and the hydrological yield of the corresponding watershed (5).
The study area with 5.5 km long of Neka watershed is located between Chaman and Bezminabad villages. According to UTM the coordinates of the study area is as flow;
XMin=699000
XMax =704000
YMin=4058000
YMax=4062000
Which is located in north latitude, in northern Iran?
The mean annual rainfall of the region is estimated to 800 mm by Isohyets method and 816.2 mm by Theissen method. The main part of the basin has very humid climate and the northern part of the basin with lower elevations has humid climate by De marten method. Based on Emberge method, the middle and northern part has cold humid and southern part of the basin with higher elevations has mountain climates.
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