بررسي انتقال رسوب و تغييرات بستر رودخانه يلفان سداكباتان همدان

Determination of the Best Model to Estimate Suspended Sediment Load in Yalfan River, Ekbatan Dam, Hamadan Province

مدل­هاي رياضي يكي از ابزارهاي مهم براي پيش بيني مقدار رسوبگذاري در بستر رودخانه­ها و مخازن سد هستند كه بر معادلات حاكم بر پديده­هاي مؤثر در انتقال، توزيع و انباشت رسوب مبتني مي­باشند. هدف از اين­ تحقيق بررسي اتتقال رسوب و تغييرات پروفيل بستر در راستاي طولي و عرضي در رودخانه يلفان­ سد اكباتان­ با استفاده از مدل2/1 GSTARS مي­باشد­. ­بررسي تغييرات مقاطع 1، 2و 3 با نتايج حاصل از شبيه­سازي مدل نشان مي­دهد كه ­داراي مطابقت قابل قبولي مي­باشد ­و نشان مي­دهد­ كه در مقطع 4 مقدار فرسايش نسبت به مقاطع قبل افزايش و در مقاطع پايين دست رسوبگذاري افزايش يافته است. به طوري­كه­ ميزان تغييرات مقاطع عرضي رودخانه از بالا به طرف پايين دست تقريبا هم­سو و هم راستا با نتايج مدل بوده و­ ميزان خطاي محاسبه شده نيز اين نتيجه را تأييد مي­نمايد­. نتايج حاصل از­ بررسي خط القعر درمدل بيان كننده افزايش ميزان رسوبگذاري به طرف پايين دست و بالا­بودن ميزان فرسايش و كف­كني در بستر رودخانه در بالا دست مي­باشد­. مقادير ضريب همبستگي وضعيت فرسايش و رسوبگذاري محاسبه شده توسط مدل2.1 GSTARS در مقاطع شبيه ­سازي شده طي مراحل كاليبراسيون و صحت سنجي 72/0و اين مقدار براي پروفيل طولي رودخانه 53/0 به دست آمد كه در حد قابل قبولي مي­باشند. بررسي­ها نشان مي­دهد­­كه مدل حجم رسوب انتقالي را ­برابر 36/1 ميليون متر مكعب برآورد كرده و نزديكي آن با مقدار اندازه­گيري شده­ به ميزان 42/1 ميليون متر مكعب نشان داد كه معادله يانگ در مدل Gstars 2/1 نتايج قابل قبولي ارائه كرده است، بنابراين­ پيشنهاد مي­شود به منظور اطمينان و كارايي بيشتر نتايج حاصل از اجراي مدل­هاي شبه دو بعدي، نتايج حاصل با استفاده از مدل­هاي ديگر مانند River intake نيز ارزيابي و اجرا شود.

Mathematical models are one of the important tools for predicting sediment yield in rivers and reservoirs. The purpose of this study was to investigate sediment transport and bed profile changes along the longitudinal and transverse directions in the Yelfan River Ekbatan dam using GSTARS 1.2 model. The studies show that the amount of erosion in the upstream sections is increased compared to the downstream sections and is almost in line with the results of the model in cross section analysis. The model estimated the volume of the sediment to be 1.36 million cubic meters and its proximity to the measured value of 1.42 million cubic meters showed that the Young's equation in the Gstars model presented 1.2 acceptable results. Introduction Rivers are affected by various factors such as geological, hydrological, geomorphological, morphological characteristics and how they are exploited. Which are plotted as erosion or sedimentation in the bed, and changes in river form.Therefore, it is necessary to ensure that they work before designing and implementing engineering projects on rivers. At present, the application of suitable mathematical models such as the GSTARS model for the hydraulic investigation of flood currents has been considered.Because it can have significant correlation between geometrical and hydraulic variables of the river, GSTARS model has a good ability to study the morphology of the river. Zahiri et al. (1977), in calculating the transverse distribution of sediment rivers using GSTARS 2.1 quasi-two dimensional mathematical model on Ghare Soo river, concluded that the performance of 2D model is appropriate in estimating transverse distribution of flow velocity and Young's relation in simulation The deposition is most accurate. Hu et al. (2010) simulated the distribution of suspended sediment concentration by quasi-two-dimensional models, using the diffusion equation across the river. The results show that using laboratory conditions and comparing them with computational data can help solve relevant equations to simulate sedimentation and estimate more accurately. The study area The Ekbatan Dam watershed is located in the southeast of Hamedan city and is one of the sub-catchments of the Ghareh Chai River located southwest of Mount Alvand. The river regime is permanently snowy-rainy and cold under semi-humid climate. Materials and Methods In this study, GSTARS 1.2 model and Young and Tuffalite sediment transport equation were used to investigate sediment transport and bed profile changes along the longitudinal and transverse directions in the 12 km interval of the Ekbatan Dam Yelfan River. First, the bed aggregation data for 9 cross-sections were randomly selected. Then the sediment data of the sections and other inputs of the model were prepared in three sections: geometric, hydraulic and sedimentary and entered into GSTARS 2.1 mathematical model. In the modeling section, the data required for model calibration and calibration were introduced to the model. Discussion and Results Surveys show that river water level slightly increased from the beginning of the interval (8-12 km downstream) to the middle of the study area and decreased downstream (4 km up to the end of the interval near the dam body) so It can be seen that the Yang model accurately simulates this process. Examination of the longitudinal profile of velocity and slope calculated by the model and examination of velocity and slope variations during the study period show that the volume model is estimated to be 1.36 million cubic meters and its proximity to the measured value is 1.42 million. The cubic meter showed that the Young's equation was well able to simulate the volume of sediment transported during these statistical years. It also increased with increasing intercept of sediment yield, but since the slope and velocity are both lower in the middle of the range than the beginning of the region and more than the bottom, Therefore, the sedimentation rate in the middle is higher than the beginning and lower in the study area. Conclusion The model simulation results show that in section 4, the amount of erosion in the bed increased compared to the previous section and sedimentation occurred on the banks of the river and erosion was the dominant sedimentation rate. However, in the downstream and near sections of the dam body, the flow velocity and slope interval decreased and the erosion rate decreased. an‎d increased sedimentation rate, indicating a good agreement of Young's (1984) model with the values obtained and the early stages of the study period. In addition, the results of the river crossing study in the model indicate an increased sedimentation rate downstream of the study area and a high erosion rate in the upstream river bed. Therefore, it is suggested to evaluate and execute the results using other models such as River intake in order to provide more reliable and efficient results from the implementation of quasi-2D models.