Author(s): Murray Konzang; Elena Carcano; Mirzi Betasolo

Linked Author(s): Murray Konzang Konzang, ELENA CARCANO

Keywords: Fish by pass passage; Flow duration curve of long term period; Eta Beta method; Biological surveys; Aquatic species demand

Abstract: The work presented herein is related to a restoration of a small hydropower plant located in the Nervia Catchment, in the village of Pigna, in north western Italy. The plant has been established in 1901 and has worked till 1965. In 1966 it has been dismantled due to the nationalization process of the electrical production carried out by the Italian country company named E.N.E.L. The solution proposed suggests the restoration of the ancient building and introduces a by pass device to fulfill fish ascends of trouts especially. Other hydraulic structures such as : hydro’s weir and the restitution opera are already present and need to be structurally reinforced. The distance between hydro’s weir and restitution opera is equal to 700 m. Inside this path the village purifier is also displaced. In order to better fulfill water’s quality requests a biological inspection has been conducted and parameters of : ph, BOD5, COD, ammonia nitrogen , nitrates, cholorides and sulphates have been evaluated. This analysis has been carried out to evaluate how the water hydropower withdrawal may influence water dilution coming from the drain’s purifier. The plant presents a total power production of P=66 kW and roughly an annual corresponding energy value of E=286 000 kWh/year while mean annual power equals to P2=32 kW. Maximum water theoretical concession Q= 1m3/s while basic environmental flow , without additional increases and seasonal biological modulations, has been set equal to EF 100 l/s. Mean annual hydroplant’s withdrawal equals to 480 l/s and topographical head reaches h= 8.69 m without energy losses. Optimum withdrawal has been proposed from the designer (Elena Carcano and others) according to the flow duration curve of long term period available for the River Nervia (data are present from 1 1 1929 up to 31 12 1975) and from the so known Eta Beta method. Such a hydrological methoid has been adopted in order to confirm the adequate streamflow set at value of 1 m3/s. Results show that the intersection between the Eta Curve and the beta curve corresponds to a streamflow value of 1.255 m3/s available 76 days a year. Therefore this method confirms information gained from flow duration curve and the maximum water concession proposed By the Water Bureau in charge. From the biological point of view, an ante operam study has been conducted in order to evaluate scenarios of suffering situations for aquatic species. The biological monitorings have been conducted relying on ELT 60 11 G1 Scubla instrument and have been performed in transepts: •Upstream section •Subtended Section •Downstream section Results show that the plant can work efficiently 8 months / year and interruptions may occur during summer season , namely from June up to October.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202238

Year: 2022