In a pressurized water conveyance system, such as a hydropower system, during hydraulic transients, maximum and minimum pressures at various controlling sections are of prime concern for designing a safe and efficient surge tank. Similarly, quick damping of surge waves is also very helpful for the sound functioning of the hydro-mechanical system. Several parameters like diameter of the surge tank, diameter of the orifice, operating discharge, working head, etc., influence the maximum/minimum surge, damping of surge waves in the surge tank, and the difference of maximum pressure head at the bottom tunnel and maximum water level in the surge tank. These transient behaviors are highly conflicting in nature, especially for different diameters of orifices (D_O) and diameters of surge tanks (D_S). Hence, a proper optimization method is necessary to investigate the best values of D_O and D_S to enhance the safety and efficiency of the surge tank. In this paper, these variables are accurately determined through numerical analysis of the system by the Method of Characteristics (MOC). Furthermore, the influence on the transient behavior with changing D_O and D_S is investigated and finally, optimum values of D_O and D_S are determined using Particle Swarm Optimization (PSO) to minimize the effects of hydraulic transients on the system without compromising the stability and efficiency of the surge tank. The obtained results show significant improvements over the contemporary methods of finding D_O and D_S for surge tank design.

Anthropogenic activities have led to the transformation of river basins and natural flow alteration around the world. Alteration in flow regimes have adverse effects on river ecosystems. Flow value changes signify the alteration extent and a number of flow related indices can be used to assess the extent of alteration in a river ecosystem. Selection of a few and ecologically relevant indices from a large set of available indices is a daunting task. Principal Component Analysis helps to reduce these large indices to a few ecologically significant indices and removes statistical redundancy of data to give uncorrelated data sets. These representative indices are useful in the primary investigation of a less studied area like the Kaligandaki River basin, Nepal. This paper uses reduced indices from the Kaligandaki River to calculate the alteration on the river section downstream of a hydropower facility using the Histogram Comparison Approach (HCA) combined with Hydrologic Year Types (HYT). The combined approach eliminates the potential underestimation of alteration values which may occur due to the exemption of hydrologic year types from the analysis, a feature equally relevant in river ecology. A new metric is used for the calculation of combined alteration using HCA-HYT in this paper. The analysis showed 60.71 percent alteration in the natural flow regime in the area past a hydropower construction, which is classified in the high alteration category. The study can be a guide for further analysis of the ecological flow management of a river section and a parsimonious approach to other areas where hydrological data is limited to historical flow records only.

Huang, X.; Suwal, N.; Fan, J.; Pandey, K., and Jia, Y., 2019. Hydrological alteration assessment by histogram comparison approach: A case study of Erdu River Basin, China. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 139–145. Coconut Creek (Florida), ISSN 0749-0208.The Erdu River is a small river in Hunan Province. This paper studies the quantitative assessment of the hydrological alterations in the hydrological regimes of the Erdu River caused by the Liujiaping hydropower station. Diurnal streamflow data between the time intervals from 1967-2013 were obtained from the Hengbanqiao station. The histogram comparison approach (HCA) and improved overall degree of hydrological alteration with new classification were used for the assessment. The hydrologic regime alteration was computed by the IHA (indicator of hydrological alteration) indices. As per the improved classification, three indices were altered at low degrees, seven -indices were altered at moderate degrees, eleven indices were altered at high degree and ten indices were altered at severe degree. The overall and improved overall degree of hydrological alteration for the Hengbanqiao station is 72% and 80.49% respectively, suggesting a high and severe degree of alteration respectively. The alteration degree of every IHA indices ranged from 32.29% to 100%. This shows that the current operation mode of Liujiaping hydropower station has severely deteriorated eco-hydrological regimes of the downstream area. Hence, there is an immediate need to operate the reservoir taking into consideration the ecological needs of the downstream areas, in order to preserve the river-ecology of the Erdu River.