شناسایی الگوهای جوی مولد سیلاب شهری و شبیه‌سازی رواناب ناشی از آن در شهر میناب

شناخت رفتار هیدرولیکی سیلاب های شهری در ارزیابی و بهسازی سیستم جمع آوری رواناب ها در شهر حائز اهمیت است. در این پژوهش برای دستیابی به این رهیافت مدیریتی در شهر میناب، ابتدا الگوهای جوی مولد سیلاب شناسایی شد. سپس رفتار هیدرولیکی سیلاب در مجاری زهکشی با مدل swmm شبیه سازی شده و برای صحت سنجی مدل از سه واقعه ی بارش متناظر استفاده گردید. نتایج پژوهش نشان داد کم فشار سودانی با عبور از دریای خلیج فارس و کسب رطوبت تقویت شد و در برخورد با کوهستان شمالی جلگه میناب بر ناپایداری آن افزوده شده و در نهایت موجب وقوع بارش سنگین و سیلاب شهری در میناب شد. نتایج حاصل از واسنجی مدل با مقادیر مشاهداتی در مولفه های دبی، عمق و سرعت رواناب با معیارهای ns و rmse بیان گر انطباق مناسب آن ها و توانایی مدل در شبیه سازی رفتار هیدرولیکی سیلاب است. خروجی مدل نشان داد که در واقعه بارش 100 میلی متری در 12 نوامبر 2015 در شهر میناب، 195 میلیون لیتر آب به راه افتاد و منهول ها و مجاری زهکشی در زیرحوزه های مسکونی و پرتراکم ظرفیت کافی برای انتقال رواناب ندارند که موجب سیل گرفتگی زیرحوزه های شهری شد. از آنجایی که شبکه زهکشی میناب ترکیبی بوده و یک خط لوله برای انتقال آب ها سطحی و فاضلاب خام شهری وجود دارد، سیلاب شهری و عدم ظرفیت کافی مجاری و پرشدگی کانال ها در زیرحوزه های مسکونی و پرتراکم موجب پس زدگی فاضلاب خام در نقاط مسکونی شد. بنابرین، نتایج این مدل نشان می دهد که سیستم دفع آب های سطحی شهر میناب نیاز به بهسازی و طراحی مناسب برای انتقال رواناب ناشی از سیلاب دارد.

Identification of atmospheric patterns of urban floods and simulation the runoff in Minab

Extended abstractIntroductionFloods are environmental phenomena that are in the category of hydrological hazards, but to identify the cause and manage strategies to control them, other environmental sciences such as meteorology, watershed management, etc. must be utilized. Because atmospheric systems play a role in the occurrence of rainfall which in combination with topographic factors, surface topology, land use and morphology of catchments based on the slope and hydraulics of rivers and urban waterways cause flooding. Therefore, in studying the problem of floods, especially in residential areas, a combination of environmental sciences can play an important role in understanding the mechanism and development of urban floods. Also, computer models have been upgraded to simulate the behavior of urban floods. Their approach is based on the conversion of precipitation to runoff, which can be evaluated and validated with results. These models are trusted in estimating the volume and flow of runoff from the flood. The hydraulic behavior of urban floods can be simulated using hydrological models, and the SWMM model has many applications in this field. In this study, we tried to determine the hydraulic behavior of floods by recognizing the patterns of flood generating patterns and estimating the volume and flow of floods in drainage channels of Minab city. The results will be provided to urban planners to improve drainage channels and duct capacity.MethodologyIn order to identify the weather patterns of floods in Minab, at first the meteorological parameters of the region during a period of 19 years (20002018) were prepared by the Meteorological Organization and atmospheric parameters including average annual temperature, minimum and maximum monthly average, 24hour rainfall, number of monthly rainfall days and number of flood days (rainfall more than 30 mm per day) were presented in the table. Next, from the floods that occurred, two urban flood events were selected and the atmospheric meteorologists of that day at the level of 500 hPa and sea level pressure were extracted from the NCEP / NCAR data center website and mapped in ArcGIS software processing environment. SWMM model was used to estimate runoff caused by urban floods and to model the hydraulic behavior of flood flow in the surface water drainage network of Minab city; in such a way the first the model was calibrated and evaluated with the events of observational floods and after its verification, the outflow from urban subbasins, water volume in drainage channels, flooding in canals and duct capacity were simulated in urban subbasins of Minab.   Results and discussionAverage annual temperature is 28.7 degrees Celsius and its maximum is in June and July with 38 degrees Celsius and its minimum in December with 19 degrees Celsius. Most of the rainfall in Minab plain occurs in November to March, which peaks in December with 22 mm. Heavy rains start in November and end in March, and in April, heavy rains have occurred once during these years, which has led to urban floods in Minab. In the first pattern, synoptic examination of flood days in Minab showed that the 500hpa trough in Iran and the low pressure of the Persian Gulf caused floods. In the second model of flood generator, the cold system from Central Iran at the level of 500 hPa and the low pressure system of Iran caused floods on the shores of the Persian Gulf and especially the Minab plain. In this study, two events of rainfall (19/1/2014) and (11/3/2015) were used to calibrate the SWMM model. The third event of 11/12/2015 was used to evaluate the model and to analyze the results. The coefficient of flow and the square of the mean squared error were used. The simulated model is compared with the SWMM model and their differences are not significant, indicating that the model is able to estimate and simulate the hydrological parameters of urban floods. From 100 mm of rainfall in Minab urban area, about 195 million liters of water has been runoff, of which about 189.6 million liters have been wasted as floods.ConclusionThe result of urban flood modeling in Minab showed that the densely populated areas of Minab city play an important role due to impermeability to urban floods and water retention. Since Hazara Castle subbasin, Velayat Park, City Center and Sheikhabad do not have enough capacity to transfer runoff during floods. With these conditions, the results of this research can be provided to city planners and designers of surface water conduction systems and urban drainage networks of Minab.