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In recent years, increasing demand for electricity, along with pollution and the depletion of fossil fuels, has encouraged countries around the world to use renewable energy. Small hydropower plants are one of the newest renewable power plants that can be built on small rivers without the need for a dam. In this article, the construction of these power plants, feasibility studies and related economic analyzes, and finally, the work done and their potential capacities, in Iran, will be discussed. The results show that there is a lot of potential for these power plants in many countries of the world, especially developing countries. Easier construction and operation, less environmental problems and the ability to participate in the microgrid are the most important advantages of these power plants. Furthermore, the construction of these power plants in rural areas and away from the network can lead to job creation; Pursue economic benefits and reduce the dependence of these areas on the main power system. Advances in research in recent years have made small hydropower plants a mature and versatile technology that, if technical, social, and environmental barriers are removed, along with appropriate legislation and incentive policies, can play a significant role in meeting the demand for electricity from renewable resources.

Background Anterior cruciate ligament reconstruction (ACLR) surgery is frequently used to manage anterior cruciate ligament (ACL) tear. The non-anatomic positioning of the graft may cause graft failure. This study aimed at evaluating the association of the ACLR outcome with factors affecting the anatomic positioning of the graft, including the tibial tunnel, femoral tunnel, and graft inclination angles. Methods A total of 37 patients, who had undergone ACLR surgery, were included in this retrospective study. All surgeries were performed by the transportal arthroscopic reconstruction technique. The tibial and femoral tunnel angles were evaluated on both anteroposterior (AP) and lateral radiographs. Graft inclination angle was evaluated on AP radiograph. Outcome measures included: International Knee Documentation Committee (IKDC), the Lachman and the pivot shift test, and KT-1000 arthrometer score. Results The mean age of the patients was 30.1 ± 9.4 years. The ACLR surgery was successful in 36 (97.3%) patients and failed in one patient (2.7%). No significant association was found between the femoral/tibial tunnel angles and outcome measures on both AP and lateral view. A negative significant correlation was found between the IKDC score and the graft inclination angle (P = 0.049, r = -0.326), indicating that with graft angle between 20° and 36°, the more horizontal graft was associated with better IKDC score. Conclusions According to the results, graft inclination angle, yet not femoral/tibial tunnel angles, were associated with the outcome of the ACLR surgery However, further studies are required to address ‎the inconsistent results of different investigations.