ارزیابی طرح های ساماندهی رودخانه با استفاده از مدل MIKE11 (مطالعه ی موردی: رودخانه ی زرینه در حومه ی شهر شاهین دژ) (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
تغییر در هندسه و مورفولوژیک رودخانه، که منجر به تغییر مشخصه های هیدرولیک جریان می شود باید همواره مورد توجه باشد. در این تحقیق شرایط هیدرودینامیکی بازه ی بالادست و پائین دست سازه ی پل وحدت در شهر شاهیندژ آذربایجان غربی به طول یک کیلومتر با نرم افزار MIKE11 در شرایط موجود و سناریوهای م ختلف متأثر از عملیات ساماندهی شبیه سازی ش د. در ش رایط موجود (پل با دهنه ی 120متری)، به ازای دوره ی بازگشت 25 سال رودخانه (دبی1200مترمکعب بر ثانیه)، سطح آب بالاتر آمده و سواحل اطراف در معرض خطر سیل قرار می گیرد. با عملیات ساماندهی و تعریض پل به دهنه ی 300 متری، علاوه بر آزادسازی حدود 90 هکتار از اراضی مجاور در دو سمت رودخانه، مقادیر سطح جریان و به تبع آن تراز سطح آب در حدود 65 سانتی متر کاهش داشته که باعث افزایش ظرفیت میزان آبگذری رودخانه (در حدود 115 هزار مترمکعب) در محدوده ی مورد نظر خواهد شد. ضمناً میزان خطای برآورد حجم جریان ( REV ) و میزان خطای نسبی در دبی اوج (REQP ) برای شرایط ساماندهی به ترتیب برابر 197/0 و 792/1 درصد بوده که در حدود 068/0 و 82/2 درصد نسبت به شرایط موجود کاهش داشته که بر اساس دامنه ی شاخص های آماری، تناسب کاملی بین داده های مشاهداتی و شبیه سازی شده وجود داشته است. این مقادیر نشانگر تأثیر بالقوه عملیات ساماندهی رودخانه در آبگذری و روندیابی جریان است.The Assessment of the River Training Plans Using MIKE11 Model (Case Study: The Zarineh River in Shahindezh City Conjunction)
IntroductionRiver training, flood control projects, and every change of river geometry will change the morphological conditions of a river and the hydraulic characteristics and flow. In fact, the goal of river training plans can be found on the basis of the initial energy equilibrium of the river. In this study, the impact of river training on the hydrodynamic conditions of the Zarrineh River in conjunction with Shahindezh city in different scenarios were investigated. The Zarrineh River training project modeling, as a general objective, is the use of hydraulic simulations to create a river water surface based on new physical, civil, and hydrological properties of a given reach. The motivations for conducting such simulations are flood plain extent mapping based on current and new scenarios and the determination of water level along the study river reach. The purpose of this project was to create maps before and after a new river training plan, all within the GIS and Autocad environment with a georefrenced origin. Study of the Zarrineh River project requires a thorough evaluation of the possible impacts that it may have on the Zarineh River, both upstream and downstream from the Vahdat Bridge. The prediction of the operation, maintenance, and repair or replacement of the bridge, requirements of existing and proposed projects are other roles that river hydraulics simulations play in the planning and design processes. The Zarineh River is a very wild river and every civil project is needed to be evaluated from different aspects, especially from new geomorphological conditions. New liberalized areas beside the river for each scenario should be determined and evaluated for new land use utilizing particularly for Eco-Tourism usagesand repair or replacement of the bridge, requirements of existing and proposed projects are other roles that river hydraulics simulations play in the planning and design processes. The Zarineh River is a very wild river and every civil project is needed to be evaluated from different aspects, especially from new geomorphological conditions. New liberalized areas beside the river for each scenario should be determined and evaluated for new land use utilizing particularly for Eco-Tourism usages. Material and methodMIKE11 was selected to simulate current and selected new river training scenarios that iteratively solve a one-dimensional energy balance to produce water elevations based on river geometry, channel roughness, flow rate, and boundary conditions. MIKE11, developed by DHI, is a software package for simulating flows in rivers. The river geometry is provided in the form of channel cross-sections at regular intervals along the direction of flow. The number of cross sections that are taken varies with study requirements and stream characteristics. About 1 km reach of the upstream and downstream includes Vahdat bridge with 14 cross sections under current situation (without bridges and without training), the bridge with 120 meters without training, the bridge with 120 m, 200 m and 300 m with bed and banks training. For the current scenarios, it is needed to predict stage, discharge, and velocity as functions of time anywhere on a river in different return periods such as 25 yr. To measure cross-sectional coordinates, previous topographic maps generated from field surveys performed with land surveying instruments were used. All information to set up the Mike model, including input data files, simulation period, time step and the name of result files and also initial and boundary conditions were determined and defined. Flow hydrographs for the project at the bridge location for all scenarios were extracted from hydraulical simulations Mike11. For Hydrograph prediction, the Saint-Venant approach with Finite Element method and Six-Point Algorithm of Abbott were used to discretize temporal and spatial elements.Results and DiscussionThe Zarrineh River project consists of Vahdat Bridge that should be modelled and it should be checked for the reliability of new area liberalization without any impact on users of Shahindezh such as municipality, regional water authority, environmental protection agency and ministry of roads and city affairs. In river training scenarios with widening bridge to 300 m, in addition to the liberalization of 90 ha areas on both sides of river banks, the water level increased about 65 cm and the maximum flow capacity increased to 115000 m3. The calibration results indicated that the estimated error rate of flow volume (REV) and the relative error in the peak (REQP) for training scenario were respectively 0.197 and 1.792%, corresponding to the current condition which were about 0.068 and 2.82 percent. The figures showed a good agreement between modeled and observed values. Vahdat Bridge with 120 lengths and 1200 m3/sec (25 yr return flow) will overflow to adjacent areas. The modelling results showed the high potential of the river training for the flood transmission and flood routing. Also, the accuracy of the simulation of unsteady flow is one dimensional for the desired range by the MIKE11 mathematical model.ConclusionThe rivertraining projects should be modelled, controlled, and evaluated for overflow problem from sidewalls. In addition, river bed and banks should be controlled so that they are not affected by water score problem. For secure hydrograph transmission in the reach of the Zarineh River and Shahindezh city conjunction, the 300 m bridge widening scenario was selected and the executive maps and detailed plans for the river training, bridge with a width of 300 meters, sidewalls and end sill structure (river bed stabilizing structure for preventing score) were provided.
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