Assessment of the possibility of operating low-pressure hydroelectric facilities in order to improve the conditions of navigation in their lower reaches

The paper provides an assessment of the projected low-pressure hydroelectric facility operation on the Volga River from the point of view of navigation conditions in its lower reach. The operating mode of the low-pressure hydroelectric facility completely depends on the hourly discharges of the Nizhny Novgorod HPP, located upstream. Significant unevenness in time of the supplied discharges from the Nizhny Novgorod HPP, which, repeating itself when discharging flows into the lower reach of the Nizhniy Novgorod low-pressure hydroelectric facility, can lead to negative consequences for shipping in terms of failure to provide transport passes and necessary depths. It is proposed to reduce the unevenness of discharges by introducing diurnal flow regulation into the low-pressure hydroelectric facility operation, aimed at changing the hydrological regime of the river section to improve the conditions and organize uninterrupted and safe navigation in the lower reach. Achievement of the regulation goal associated with minimization of interval deviations of the supplied flow rates from Nizhny Novgorod HPP from the daily average values and the fulfillment of the restrictions on the hydrological regime of the low-pressure hydroelectric facility ponds, is achieved by two control options (three-stage and two-stage). The study used the methods of mathematical statistics and probability theory, optimization of management decisions. The methodology of the mathematical model limitations’ nonfulfillment elimination for solving the problem and optimization of the low-pressure hydroelectric facility daily hydrograph is presented. Using a specific example, the problem of diurnal regulation of discharges is solved and the obtained effect is described.

Risk assessment and source apportionment of trace elements in multiple compartments in the lower reach of the Jinsha River, China

Studies on trace element (TE) pollution in abiotic matrices have typically focused on water, sediment, and soil, either separately or in pairs. The importance of multi-media connectivity has been ignored. This study analyzed the concentrations of 6 TEs in three connected environmental compartments of a 28-km section of the lower reach of the Jinsha River. The ecological risk posed by TEs was higher in soil than in sediment. The contribution of exposure pathways to human health risk were ranked as ingestion > dermal contact > inhalation. An improved regional environmental risk index (RERI) method was then developed to evaluate the comprehensive risk on both ecology and human health caused by TEs. The average RERI value was generally higher in the wet season (0.42) than in the dry (0.41) and dry-to-wet transition seasons (0.08) because of the combined effects of the high TE concentrations in riparian soil and the long exposure time. Source apportionment indicated that industrial activities, weathering of parent rock, and agricultural activities were possible sources of TEs in this region. The methods and results of this study could inform local environmental management and provide references for similar cases wherein multiple compartments of river systems should be considered.

Roughness into the Channel Create the Flood Situation - A Case Study at Lower Reach of Shilabati River Basin, Paschim Medinipur, West Bengal

Roughness into the channel of streams and rivers determines several important hydraulic parameters must be properly represented in models for estimating water discharge and sediment transport. Hydraulic parameters mainly gradient, hydraulic radius, width, width-depth ratio, wetted perimeter and cross sectional area are considered for analysing the ability of channels to carry discharge but resisting forces are opposing component of this movement. This paper reviews to evaluate the different approaches used to identify the roughness and to understanding of how flow resistance is created by roughness in open channel flows. The Shilabati river basin embraces a portion of the eastern fringe of the Chotonagpur plateau. South west monsoon is the principal source of rainfall in this area. After the heavy storm, the low lying depression in the lower reach of this catchment attracts huge flood water and sediments from it upper catchment, sub-tributaries and larger catchments of neighbouring rivers mainly Damodar, Darakeswar, and Kangsabati. The upper courses are steeper (0.84) and rocky facilitating easy drainage, that gradually concentrates at lower reach as it lost its capacity due to sudden reduction of gradient (Gadghat, 0.08; Bandar, 0.02). In the Shilabati river the cross sectional area changes through time in response to fluctuations in discharge. Channel slopes near these gauging stations are surveyed, that shows continuously decreasing tendency towards lower catchment. Capacity of channel is measured by conveyance of flow. Roughness coefficient value at three gauging station (Banka 0.50, Gadghat near Ghatal 0.82 and at estuary, Banka,1) measuring by the Manning’s equation depicts that the resistance to flow increases steadily at downstream. Channel substrate mainly vegetation and netting also influences the boundary roughness and flow resistance. Friction from sediment load mainly grain roughness are responsible for generating resistance which steadily declines movement and create jamming of water which ultimately leads to flood and water storage situation.