تعيين مناطق مستعد سيل با استفاده از پتانسيل‎سنجي عوامل موثر (مطالعه موردي: رود شاهرود)

Flood Prone Areas Using Surveys to Determine the Potential Factors (Case Study: River Shahrood)

سيلاب و سيل‎زدگي يك پديده عام در ايران و يكي از زيان‎بارترين رخدادهاي امروزي به‎شمار مي‎رود كه بيش از هر مخاطره ديگر، جان و مال انسان را به خطر مي‌اندازد. هدف اين پژوهش شناسايي عوامل موثر بر رخداد سيلاب در حوضه رود شاهرود، براي برنامه‌ريزي مناسب محيطي است. براي دستيابي به اين هدف، داده‌هاي دبي و بارش ايستگاه‎هاي منطقه طي يك دوره مشترك پانزده‎ساله، از سازمان منابع آب ايران و هواشناسي كشور اخذ و تجزيه تحليل شدند. همچنين يازده خصوصيت فيزيوگرافي زيرحوضه‎ها، ازجمله مساحت، تراكم آبراهه اي، ضريب انشعاب و... به‎كمك نرم‎افزار GIS محاسبه و استخراج شد. براي تعيين عوامل موثر و پتانسيل سيل‌خيزي زيرحوضه‌هاي حوضه آبريز شاهرود، روش‌هاي تحليل مولفه‌هاي اصلي و تحليل خوشه‌اي به‎كار گرفته شد؛ به‎گونه‌اي كه 27 متغير زيرحوضه‌ها در قالب چهار مولفه اصلي خلاصه‎سازي شد. سپس پتانسيل سيل‎خيزي منطقه بر اساس نمرات عاملي هر يك از مولفه‌ها، به‎صورت جداگانه با روش خوشه‌بندي سلسه‎مراتبي وارد تعيين و نقشه‌هاي خروجي ترسيم شدند. نتايج نشان مي دهد كه مولفه‌هاي دبي با وزن 7/45 درصد، بارش با 7/31 درصد، حداكثر بارش تابستانه با 6/12درصد و حداكثر بارش فصل زمستان با وزن 9/6 درصد، داراي بيشترين تاثير در ايجاد سيلاب هستند، همچنين برخي از ويژگي هاي فيزيوگرافي حوضه با ادغام در مولفه اول و دوم، در تشديد آن موثرند.

Introduction Climatically hazards, such as drought, floods and storms, can extremely influence on natural ecosystems and human societies. Flood and inundation is a public problem and its occurrence has prevailed in major regions of Iran. The area of flooding regions was estimated about 91 million of hectares. It meaning that 55 percent of the area of country effect on producing runoff and the intensity of flood in about 42 million of hectares is moderate to very much. Past investigations indicate that annual growth rate of the flood hazards in during periods of 1331-1370 was about 4 percent and of financial damages was 6 percent. On the other hands, growth rate of the number of flood in decades 30 and 70 was 131, 175 and 229, respectively. the recognition of equal region is primary necessity in planning and its purpose is identify effective factors on occurrence of flood in Shahroud river basin and zonation of potential of flood in the study area. Sharoud basin is a western sub basin of Sefidroud river and include of Joustan and alamout sub basins. Methodology For achieving this research we use of advanced statistical method. First, was collected the daily and monthly data of discharge in all hydrometric stations of the basin. with regard to distribution of stations and data quality, 7 station with a same period in 15 years(1370-1385) was selected. Then in this selected station, 11 parameters of physiography of basin include: area, mean height, mean slope, drainage density of, branchin ratio, length of biggest canal, length and width of equivalent rectangle, ratio of elongation, time of concentration and linear slope calculated with using topographic maps, geologic maps, digital maps of DEM SRTM 30 meters and ArcGis software and extracted; These parameters together mean and extreme seasonal discharge and mean and extreme seasonal rainfall used as selected parameters. Results and Discussion In order to reducing number of parameters and excavating main factor used of principal components analysis method. In calculating the principal components and analyzing factors used two important values, namely eigenvalues and eigenvector. Eigenvalues obtained from total squares correlation coefficients for all variables by a certain factor. The calculated values is the Specific value of extant factor that indicate the power of factor in explaining the variance of the variables set. After selecting the parameters and set the appropriate mode depending on the research purpose (in accordance with zoning requirements of subbasins is used the array R), 27 parameters were statistically analyzed in this study, is summarized in the four components with 97.09 percent of the total variance. Conclusion The first component is the discharge of subbasins with weight 45.7% and its eigenvalue is 18.6 that are associated with the slope, drainage density and branching ratios. The second component, with power of explaining 31.8% of the total variance and eigenvalue of precipitation is 4.9. Maximum precipitation in summer, with 12.6% of variance and eigenvalue 2.8 is the third component. Maximum precipitation in winter, 6.9% of the total variance and eigenvalue 1.7, is the fourth component.