بررسی انتقال رسوب و تغییرات بستر رودخانه یلفان سداکباتان همدان

مدل های ریاضی یکی از ابزارهای مهم برای پیش بینی مقدار رسوبگذاری در بستر رودخانه ها و مخازن سد هستند که بر معادلات حاکم بر پدیده های موثر در انتقال، توزیع و  انباشت رسوب مبتنی می باشند. هدف از این تحقیق بررسی اتتقال رسوب و تغییرات پروفیل بستر در راستای طولی و عرضی در رودخانه یلفان سد اکباتان با استفاده از مدل2/1   gstars می باشد . بررسی تغییرات مقاطع 1، 2و 3 با نتایج حاصل از شبیه سازی مدل نشان می دهد که دارای مطابقت قابل قبولی می باشد و نشان می دهد که در مقطع 4 مقدار فرسایش نسبت به مقاطع قبل افزایش و در مقاطع پایین دست رسوبگذاری افزایش یافته است. به طوری که میزان تغییرات مقاطع عرضی رودخانه از بالا به طرف پایین دست تقریبا هم سو و هم راستا با نتایج مدل بوده و میزان خطای محاسبه شده نیز این نتیجه را تایید می نماید . نتایج حاصل از بررسی خط القعر درمدل بیان کننده افزایش میزان رسوبگذاری به طرف پایین دست و بالا بودن میزان فرسایش و کف کنی در بستر رودخانه در بالا دست می باشد . مقادیر ضریب همبستگی وضعیت فرسایش و رسوبگذاری محاسبه شده توسط مدل2.1  gstars در مقاطع شبیه سازی شده طی مراحل کالیبراسیون و صحت سنجی 72/0و این مقدار برای پروفیل طولی رودخانه 53/0 به دست آمد که در حد قابل قبولی می باشند. بررسی ها نشان می دهد که مدل حجم رسوب انتقالی را برابر 36/1 میلیون متر مکعب برآورد کرده و نزدیکی آن با مقدار اندازه گیری شده به میزان 42/1 میلیون متر مکعب نشان داد که معادله یانگ در مدل gstars 2/1 نتایج قابل قبولی ارائه کرده است، بنابراین پیشنهاد می شود به منظور اطمینان و کارایی بیشتر نتایج حاصل از اجرای مدل های شبه دو بعدی، نتایج حاصل با استفاده از مدل های دیگر مانند river intake نیز ارزیابی و اجرا شود.

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

AbstractMathematical 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.IntroductionRivers 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 quasitwo 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 quasitwodimensional 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 areaThe Ekbatan Dam watershed is located in the southeast of Hamedan city and is one of the subcatchments of the Ghareh Chai River located southwest of Mount Alvand. The river regime is permanently snowyrainy and cold under semihumid climate. Materials and MethodsIn 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 crosssections 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 ResultsSurveys show that river water level slightly increased from the beginning of the interval (812 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.ConclusionThe 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 quasi2D models.