Evaluation of techniques used to protect tailrace fishes during turbine maneuvers at Três Marias Dam, Brazil

Abstract

Turbine dewatering and stop/startup may lead to the death of tons of fish at Brazilian power dams. The Três Marias Dam (TMD) on the São Francisco River has adopted two techniques to reduce the quantity of fish, mostly mandi (Pimelodus maculatus, Pimelodidae), affected by these maneuvers. They are: (i) spill before turbine dewatering to attract fish out of the tailrace, and (ii) fish screens in the stop log slots during turbine stop/startup to prevent fish from entering the draft tube. Here, we investigated whether spill and fish screens reduced the quantity of fish affected by turbine dewatering and stop/startup at TMD. We also determined whether the biomass of mandi trapped during turbine dewatering may be predicted by turbine discharge (Q) and/or catch per unit effort (CPUE) of mandis in the tailrace. Due to insufficient statistical power, our data were inconclusive as to whether spill attracted mandi out of the tailrace. We verified that the presence of fish screens significantly reduced the biomass of dead/moribund fish during turbine stop/startup. The biomass of mandis trapped in the draft tube during turbine dewatering was mainly influenced by Q (r 2 = 0.67), followed by CPUE (r 2 = 0.49). Since the trapped fish biomass correlated negatively with Q, we recommend that Q be maximized before turbine dewatering to reduce quantity of mandi trapped in the draft tube. The information presented here may be useful for reducing the quantity of fish affected by turbine maneuvers at TMD, as well as other dams.Drenagem e parada/partida de turbina podem provocar a morte de toneladas de peixes em usinas hidrelétricas brasileiras. A usina de Três Marias (UTM), rio São Francisco, adotou duas técnicas para reduzir a quantidade de peixes, principalmente do mandi (Pimelodus maculatus, Pimelodidae), afetada durante essas manobras. Essas são: (i) vertimento antes da drenagem de turbina para atrair peixes para fora do canal de fuga, e (ii) grades nas guias das comportas ensecadeiras durante paradas/ partidas para prevenir a entrada de peixes no tubo de sucção. Neste estudo, investigamos se o vertimento e as grades reduziram a quantidade de peixes afetados durante drenagem e parada/partida de turbina na UTM. Nós também determinamos se a biomassa de mandis aprisionados em drenagem de turbina pode ser predita pela vazão da turbina (Q) e/ou pela captura por unidade de esforço (CPUE) de mandis no canal de fuga. Devido ao poder estatístico insuficiente, nossos dados foram inconclusivos se o vertimento atraiu mandis para fora do canal de fuga. Verificamos que a presença das grades reduziu significativamente a biomassa de peixes mortos/moribundos em paradas/partidas de turbinas. A biomassa de mandis aprisionada no tubo de sucção nas drenagens foi influenciada principalmente pelo Q (r 2 = 0.67), seguida da CPUE (r 2 = 0.49). Como essa biomassa foi negativamente correlacionada com Q, recomendamos que Q seja máxima antes da drenagem para reduzir a biomassa de mandis aprisionada no tubo de sucção. Acreditamos que as informações apresentadas...

Factors Influencing Movements of Two Migratory Fishes within the Tailrace of a Large Neotropical Dam and their Implications for Hydropower Impacts

“…Collectively, our findings for Mandi, including its longer residency within the tailrace, higher median of the number of visits to the tailrace and responses to turbine and spillway discharges indicate that it is more sensitive, and potentially more vulnerable to dam operations, relative to Curimba. This may be compounded by the high swimming performance and benthic orientation of Mandi, which can facilitate entry into the draft tubes of turbines, explaining why it is the species that appears to be most affected by turbine operation (Santos et al , ; Andrade et al , ). With an increased understanding of the behaviour and vulnerability of both species studied here, dam operations may be modified to reduce the entrainment of fishes in the draft tubes.…”

“…At the Três Marias Dam (TMD), located on the upper São Francisco River Basin in central Brazil, large aggregations of fish are frequently observed in the tailrace of the dam, where they may be at risk of entry into the draft tubes during operation of turbines. Two of the most common species affected include Prochilodus argenteus Spix & Agassiz, 1829 and, Pimelodus maculatus Lacepède, 1803 (Andrade et al , ). Both are abundant migratory fish and considered important species for commercial fisheries (Sato et al , ).…”

Temporal variation in fish community in the tailrace at Três Marias Hydroelectric Dam, São Francisco River, Brazil

“…The latter species is the one most impacted by turbine maneuvers and draft tube dewatering at TMD (Andrade et al, 2012). In both cases there is a high risk of fish mortality or injuries.…”

“…Downstream from the dam, there are changes affecting fluctuations in natural discharge and control of the flood regime (Baxter, 1977;Freeman et al, 2001;Gehrke & Harris, 2001;Zdankus et al, 2008). Damming interrupts fish migration (Dugan et al, 2010), causes gas supersaturation due to the incorporation of atmospheric gases by spillways and turbines (Schisler & Bergersen, 1999;Urban et al, 2008), affecting certain fish species due to maneuvers of turbines and spillways (Andrade et al, 2012;Schilt, 2007) and can increase levels of predation as a result of the high density of fish that accumulate immediately downstream (Agostinho et al, 2007). Dams also affect downstream populations by altering water quality and habitat conditions (Balciunas & Zdankus, 2007;García et al, 2011), with consequences for both resident and migratory fishes (Lessard & Hayes, 2003).…”

Seasonal and diel changes in fish distribution in a tropical hydropower plant tailrace: evidence from hydroacoustic and gillnet sampling

“…Some operational procedures, such as draft tube dewatering and stop/start up, impose mortality risk for those fish in the tailrace and can cause death of large numbers of individuals (Andrade et al . ). Thus, characterising the ichthyofauna downstream from hydropower plants could guide measures to minimise the direct effects of plant operation on fish (Loures ).…”