نشریه سد و نیروگاه برق آبی ایران
پیاپی 2 (تابستان 1393)

In the literature, optimization of reservoir operation has been mostly carried out to achieve certain objectives including water and/or energy supply, flood control, and environmental preservation. These objectives can be less important for the reservoirs with high sedimentation. Sefid-Rud Reservoir in Iran has been facing extreme sedimentation rates in the past. A major challenge in operation of this reservoir has been to create a tradeoff between sediment removal and water supply to downstream users. The lack of modeling tools for balancing sediment removal with water supply objectives has been the main driving force behind this study. In this paper, a new approach is proposed for monthly reservoir operation optimization of Sefid-Rud Reservoir considering water supply and sediment removal objectives concurrently. The model minimizes the total deficit in supplying demands and maximizes the total volume of sediments removed from the reservoir. The sediment outflow is determined debased on Tsinghua university flushing equation. A new evolutionary algorithm “Imperialist Competitive Algorithm (ICA)” is used to solve the resulted nonlinear optimization model. Five scenarios were assessed for depending on the relative weights assigned to each of objectives of sediment removal and water supply. Based on the results obtained, the feasibility of increasing efficiency of flushing operation while supplying downstream water demands was illustrated. Moreover, the significance of the improved system’s operation with higher long-term reliability of supplying downstream water demands and sediment removal, compared to historical operation, was investigated.

Small hydroelectric power stations became attractive for generating electrical energy after the oil price crisis of the seventies. The main component of a small hydroelectric power is the turbine part. Cross flow turbine is one of the impulse turbines types that can be applied for a wide-range of water heads and flow rates. In the present study, an installed cross flow turbine with rated capacity 340kW that are currently utilized only 180 kW in its rated point (50 m, 0.840 m3/s, N= 600 rpm), has been analyzed with using CFD for considering the reason of its rated low output power. Turbine geometry included runner, casing, shaft, nuzzle and guide vane has been simulated using Ansys/CFX flow solver to determine the turbine characteristic curves in various rotational speeds. Some simulated points have been verified using available real data of actual turbine.

Given the important role of hydropower in peak electricity management, Middle Eastern countries are actively pursuing development of more hydropower resources by construction of large dams. Nonetheless, climate change is expected to affect the future productivity of hydropower by influencing the hydrologic cycle and different climate variables in the region. While reactive plans to minimize climate change impacts on hydropower production have been implemented in the developed world, the developing world can still benefit from proactive actions. Studies of climate change impacts before and during implementation of hydropower projects can result in timely responses and adaptation to climate change, with a potential with considerable cost savings. This study investigates the potential impacts of climate change on the hydropower systems in the Karkheh River Basin —the third largest river basin in Iran— in terms of potential for hydroelectricity generation. A simulation model is developed to examine how hydropower generation levels vary for different future climate change scenarios in this representative Middle Eastern basin. The obtained results suggest that the existing operation rules and design specifications, developed based on the historical climatic conditions, can lead to inefficient operations of the hydropower in the basin. Due to insignificant streamflow reductions in short-term, hydropower production may not change considerably in the near future. However, serious hydropower generation deficit is expected in the mid-term and long-term horizons in the Karkheh River Basin. Therefore, adaptation to the future climate change conditions and revision of the operation rule curves and design specifications is essential to optimal hydropower operations in this basin.

An earth/rockfill dam is always located in a valley of a river which can have different shapes as a natural structure. Valleys normally appear regularly or irregularly and they can be idealized in the shapes of V, U, rectangular and etc. the shape and type of the valley affect all steps of a dam project, from initial studies up to construction and dam behavior. Consequently, the shape and size of the valley as an effective factor should be considered in all steps of the project because narrow valleys are the circumstances which are always a barrier of constructing the earth dams. So the behavior of earth dams in narrow valleys is affected by 3D effects of valley. The geometry of dam and especially the ratio of crest length to dam height are affecting the 3D behavior. Consequently 3D analysis seems to be necessary for large dams in narrow canyons. Current paper is an attempt on estimation of the 3D effects of narrow valley on the behavior of Marun rockfill dam with crest length of 345m and height of 165m (L/H=2.1), which is located in the south west of Iran. In accordance with this goal, 2D and 3D analyses of dam have been carried out by FEM method and the results are compared with each other. According to the analyses results it’s seemed that in the narrow valley of Marun dam, there are some 3D effects which couldn’t be applied to the model through 2D analysis. Both of analyses showed a same trend for results and the reductions and increases were the same. But the eye taking difference between these two analyses was the overestimation of results of 2D analysis. Both displacements, vertical and horizontal ones, in 2D analysis results were more than 3D values and even more than natural values. Comparison of results may confirm the necessity of 3D analyses for these types of dams. It could be stated that an earth dam in a narrow canyon is a structure which should be considered as a 3D volume. In this situation, the 3D effects applied with the valley aren’t negligible and a 2D analysis cannot include this 3D behavior and would result in overestimated results which aren’t reasonable at all. Anyhow, the results of this article belong to a case study which has its special conditions and wouldn’t be applied for all the dams in narrow valleys because each case has its certain conditions and consequently its different manner.