چکیده:
In order to understand the course of a river in human life as water supplier which causes destruction and damage, it is necessary to determine the flood zone with great accuracy. The aim of the present study is determining the flood zone of Khesht river in Khesht and Komarej division in Kazeroon city, situated in south western of Fars with the length of 10 Km. In this research on of the newest type of aerial photos was used to determine the studied terrains and scope.ً the regional Orthophotos (aerial photos which reduce the diversions related to camera and change in altitude after photography and then they are made after combination with digital elevation model by means of special software) with an accuracy of 1:2000 have been modelled incorporation with HEC-GeoRas extension and HEC-RAS software with return period of 25, 50 ,100 years. In order to achieve this we used Orthophotos in HEC-GeoRas extension to extract (access) the geometric features for 202 cross sections and calibration of hydraulic HEC-RAS model. We estimated water profile in return period of 25, 50, 100 years. Also we used HEC-GeoRas extension to show the flood zone of river. The results showed that there were no significant differences in flood zones In addition river condition in the mentioned return periods was subcritical.
خلاصه ماشینی:
(Refer to the page image) (Refer to the page image) Figure 1: A view of the cross-section obtained from ground surveying Figure 2: A view of the cross-section extracted from an Orthophoto In the present research, in order to determine the riverbed of the Shaporkhasht River between the villages of Chorum and Chiti with a length of 23 km, using regional photos with a precision of 1:2000 and a digital elevation model with a precision of 1:1, by utilizing the HEC-GeoRAS extension, for the purpose of extracting the geometric characteristics of the river by introducing 344 cross-sections and Manning's roughness values for each of the sections in the bed, floodplains of the left and right banks, flow characteristics, and hydraulic specifications in the HEC-RAS model, flow characteristics for return periods of 25, 50, and 100 years are calculated, and then the output information from the HEC-RAS model is transferred to the HEC-GeoRAS extension to estimate and display the flood zone for the return periods calculated in the model.
Table 1- Physiographic characteristics of the Shaporkhasht River catchment basin Row Parameter Unit Value 1 Area km2 2141/76 2 Perimeter km 402/4 3 Main stream length km 110/9 4 Gravelius coefficient - 2/43 5 Circularity ratio - 0/17 6 Equivalent rectangle length km 189/9 7 Equivalent rectangle width km 11/3 8 Elongation ratio 0/59 - 9 Shape coefficient - 0/17 10 Lca - 42/2 11 Maximum elevation m 3018 12 Minimum elevation 527 m 13 Average basin slope percentage 28/7 14 Shape factor Li 16/8 15 Lm 89/1 km 16 SCS method concentration time 11/8 h [ (Refer to the page image) Figure 3: Images of the existing condition of the studied river reach Findings and Discussion - Determination of flood zone - Hydraulic simulation of flow using HEC-RAS software In summary, the information required by the HEC-RAS model for the hydraulic simulation of flow in the river includes: Geometric or physical characteristics of the river, flow discharge, flow resistance coefficient, and boundary conditions.
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