نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری آبخیزداری، دانشکدة منابع طبیعی، دانشگاه تهران، ایران

2 استادیار دانشکدة منابع طبیعی، دانشگاه تهران، ایران

3 استاد دانشکدة منابع طبیعی، دانشگاه تهران، ایران

چکیده

اتخاذ روش‌های صحیح در مدیریت آبخیزهای شهری برای کاهش خطرها امری انکارناپذیر و ضروری است. لازمة این امرْ برآورد میزان رواناب با درجة اطمینان بالاست. یکی از عواملی که بدون شک، تأثیر زیادی در دبی اوج و حجم رواناب دارد زمان تمرکز است. هدف از این تحقیق انتخاب بهترین روش از میان فرمول‏های تجربی برآورد زمان تمرکز است. برای تعیین زمان تمرکز واقعی از روش صحرایی مبتنی بر اندازه‌گیری زمان پیمایش آب با استفاده از جسم شناور استفاده شد. به منظور انتخاب بهترین فرمول تجربی از معیارهای آماری‌ـ شامل درصد خطای نسبی (RE)، میانگین مربعات خطا (RMSE)، میانگین درصد خطای نسبی (RME)، ناش‏ساتکلیف (NS)، و ضریب تبیین (R2)‌ـ استفاده شد. سپس، درصد اختلاف مقادیر به‌دست‌آمده از فرمول‏های تجربی با مقادیر واقعی اندازه‏گیری‌شده مقایسه شد. در این مطالعه، بر اساس نتایجِ مقایسة درصد خطای نسبی در هر بازه، فرمول‏های تجربی کالیفرنیا، چاو، کارتر، و فدرال به‌تربیب با درصد خطای 7/2، 9/2، 4/4، و 7/4 برای بازة ۲، رابطة کربای- هات‏وی با درصد خطای 1 برای بازة ۳، رابطة ونتورا با درصد خطای 5/8 برای بازة ۹، و، در نهایت، رابطة هیدروگراف استدلالی با درصد خطای 8/4 برای بازة ۱۰ بهترین برآورد را داشته‏اند. در نتیجه، پیشنهاد می‏‌شود در مناطقی که خصوصیاتی نظیر این بازه‏ها دارند، با توجه به اطلاعات موجود، از رابطه‏ای استفاده شود که کمترین درصد خطا را دارد. در نهایت، مشخص شد فقط روش هیدروگراف استدلالی برای کل حوضه کمترین خطا را دارد و جواب مناسبی ارائه داده است.

کلیدواژه‌ها

عنوان مقاله [English]

Selection of the best empirical formula to estimate time of concentration in urban watersheds (Case study: Mahdasht town)

نویسندگان [English]

  • ali shahbazi 1
  • Shahram khaliqi sygarodi 2
  • Arash Malekian 2
  • Ali Salajegheh 3

1 PhD. Candidate, Faculty of Natural Resources, University of Tehran, Karaj, Iran

2 Assistant Professor, Faculty of Natural Resources, University of Tehran, Karaj, Iran

3 Professor, Faculty of Natural Resources, University of Tehran, Karaj, Iran In

چکیده [English]

In order to decrease the risks associated with the management of urban watersheds, the use of proper methods is an essential task to estimate the runoff with a high degree of confidence. Time of concentration is one of factors that impacts on peak discharge and runoff volume. The objective of this study is to select the best method among the empirical formulas for estimating the time of concentration. In this study, for determination of actual time of concentration, the field method based on measuring the travel time by using floating-object method was employed. To select the best empirical formula of the time of concentration, the statistical criteria including percentage Relative Error (RE), Root Mean square error (RMSE), Average percentage Relative Error (RME), Nash - Sutcliffe criteria (NS) and determination coefficient were used. Then, differences among the estimations obtained from empirical equations were compared with the actual values. The results of this study based on comparison of the relative error in each interval showed that in the reach No. 2, empirical formulas of California, Chow, Carter and Federal Aviation, with percentage error of 2.7, 2.9, 4.4 and 4.4 have showed the best estimation, respectively. The equation proposed by Kirby with percentage error of 1 in the reach No. 3, the equation of Ventura with percentage error 8.5 in the reach No. 9 and the equation of rational hydrograph with percentage error 4.8 in the reach No. 10 have showed the best estimates. Therefore, it is recommended to use the empirical formula that has the lowest percentage of error for areas with features similar to the studied reaches. In general, the results show that only rational hydrograph method in all of the reaches has the lowest error and then provides the most proper estimates compared than others.

کلیدواژه‌ها [English]

  • empirical formula
  • rational hydrograph
  • time of concentration
  • travel time
  • Urban Watershed
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