عنوان مقاله [English]
Studying flood reasons and Its Risks in Zunuzchai Catchment Basin, Using HEC-HMS Hydrological Model and Fuzzy Logic
Flood is considered as one of the most common and costly risk, which results in harsh physical, social and economic damages and causalities in urban and rural areas. Hence, evaluation of flood risks is of great importance in line with risk management of flood and its potential effects on human, ecosystem and natural resources. Flood hazard mapping and risk area delineation is a risk that can be achieved through integrated GIS and remote sensing applications. In this regard, preparing flood risk plans is one of the most important measures for flood risk management, which can be taken in the form of GIS. The main function of GIS is storing and connecting several digital data bases and different subjective layers, graphical representation of such data in the form of maps and examining connection way of the layers. These layers are the main key elements needed for flood risk management. The aim of the present research study is to examine flood risk in catchment basin of Zunuzchai. The study area has been located at East Azerbaijan Province (political-administrative zone of Maranad county). The study area is about 323 square KM, being located at geographical coordinates of 380 and 32’- 380 and 46’ northern width and 450 and 40’-450 and 59’Eastern length.
Materials and Methods
The ultimate goal of the present study is spatial evaluation of flood risk at Zunuzchai catchment basin. The data employed in this study are: topographical maps at scale of 1:500000, geographical maps at scale of 1:100000 (ref. Geology Organization of the country), area soil maps (ref. Regional Water Organizational of East Azerbaijan Province), Height Digital Elevation Model image obtained from ALOS-PALSAR satellite with spatial isolation power of 12.5 m, Sentinel-2 satellite images with spatial isolation power of 10m, Google earth satellite images, meteorological data along with data of registered spate (hyetograph) and hydrometric data along with floods hydrographs. In the present study, HEC-HMS along with HEC-GEoHMS hydrological modeling methods were used for evaluation and identification of flood-prone areas or areas with higher potential of changing rainfall to runoff. After entering the spatial data into the HEC-HMS model, other parameters of the model were determined. In this study, SCS curve number for losses, SCS unit hydrograph method for conversion, monthly constant for base flow and Muskingum method for flood routing were used.
This model is a mathematical model, which can restore amount, peak flow, and time of reaching peak flow through simulation of the catchment basin behavior. Moreover, for spatial evaluation of the study area flood potential, fuzzy overlay technique of subjective layers was used in GIS .
Results and discussion
Results of rainfall-runoff and fuzzy zoning of flood risk at Zunuzchai catchment basin might be summarized as follows:
-Although sub-basins with higher area have higher peak flow, there is not significant correlation between sub-basin area and peak flow amount. This shows that the role of other basin factors in runoff generation amount and its transfer manner is of great importance. In this regard, slope, land use, plant coverage and sub-basin form is of great importance due to higher influence on parameters such as permeability, rainfall loss, delay time and concentration time.
-Most of the downstream sub-basins have lower runoff generation power. Lower slope, higher permeability and plotted agricultural lands and gardens are among the main reasons of increased loss and decreased runoffs resulted from rainfall.
-Flood peak of Zunuzchai catchment basin for rainfalls with return period of 2 years (about 15 mm) is about 42 cubic meter per second, which increases to 129 cubic meter per second for rainfalls with return period of 10 year (30.4 mm). Such amount of flow does not cause such flood risk for residential areas in the floodplain. However, peak flow of flood for rainfalls with return period of 50 year and above reaches 200 cubic meter per second and even more. In case of not observing river privacy, especially in the downstream area, this might result in serious risk. The origins of such floods are upstream and middle-stream of the study basin.
-About 3.5% of the Zunuzchai catchment basin is in too high risk class, 7.3% is in high risk class, 10.4 is in normal risk class , 17.9% is in low risk class and 60.9% is in very low risk class. In fact, the major part of the study catchment basin in the upstream is at low and very low risk classes. This mainly can be related to high altitude, steep slope, higher plant coverage density, higher bulge, lower drainage density and less depth of valleys. The zones prone to flood have been distributed mostly at the downstream areas and also around main waterways in the middle parts of the study basin.
Findings of the study indicated higher efficiency of the employed approach in identification of flood-prone zones. The flood prone zones are in sub-basins of middle stream of Zunuzchai catchment basin. Presence of geological formations, soils with lower permeability, higher slope, lack of plant coverage or weak plant coverage, concentration time and less delay time are among the most important reasons of much runoff and rapid lead of runoffs caused by rainfall in this basin. Flood prone zones of the study area are mostly accordant to floodplains adjacent to the main waterways and Alluvial fan of Zunuzchai. From this point of view, about 11% of the study basin is in too high risk and high risk classes. Adjacency to river, gentle slope, higher drainage density, lower values of the land bulge index, and higher values of valley depth index and joining the two main waterways in the study basin facilitate flood spread in these zones. Presence of residential areas adjacent to the main waterways of the area and whole or partial location of them on the floodplains has increased risk of flood, considerably.