Twenty-six years of uneven changes in low flows due to different uses and operation of a large dam in a semiarid river

Abstract

Little is known about the hydrological impact of the dams in Brazil, despite the rising energy demand and untapped potential. The Paraguaçu River's discharge has been greatly impacted since 1986 by a large dam built in the lower course of the river. In the 26 years of the history of the dam, the minimum discharges have followed different operational guidelines: 1) there was no established discharge minimum between 1987 and 1996; 2) the discharge minimum was 11 m³s-1 between 1997 and 2004; and 3) hydropower generation began in 2005, when local wet season discharges were either 80 m³s-1 or 160 m³s-1 , and dry-season pulses of 10 m³s-1 , which were adopted as minimum stream flow. The mean annual dam discharge between 1987 and 2012 was 17.4% less than the incoming river flow. While rare events of daily null flow exist in the historic records, hundreds of occurrences of daily null flow have been observed in the outgoing discharge since 1987. Other important hydrologic alterations (IHAs) have included: the one-day minimum, the 3-day minimum and the number of low-discharge pulses. Ecochange analysis indicates an overall discharge loss (ecodeficit) in the system. The period of dam operation has coincided with a noticeable drop in the natural river discharge, when the mean discharge was 32% lower than in the pre-dam period (1947-1986

New records of the alien cup-corals (Tubastraea spp.) within estuarine and reef systems in Todos os Santos Bay, Southwestern Atlantic

“…Moreira et al (2014) experimentally showed high mortality rates of T. tagusensis and T. coccinea when exposed to low salinity (i.e., 0, 5, 10 practical salinity units). However, the Tubastraea invasion in the Paraguaçu estuary may have occurred due to the predominance of marine salinity levels (Genz et al, 2008;Reis-Filho et al, 2010;Genz & Lessa, 2015). This condition is likely to be associated with the building of the Pedra do Cavalo Dam in 1985 and Pedra do Cavalo Hydroeletric Power Plant in 2005 on the upper estuary (Fig.…”

Long-term Variability of the Salinity Field in a Large Tropical, Well-Mixed Estuary: the Influence of Climatic Trends

“…2D), the dry season on the coast. With the construction of Pedra do Cavalo dam (4.63 × 10 9 m 3 volume) in 1986, built for urban water supply, flood control, and hydroelectric power generation, the Paraguaçu River discharge became highly regulated (Genz and Lessa 2015). While the average river discharge for the period 1986 to 2015 was 69.0 m 3 /s, the average flow released by the dam was 55.3 m 3 /s.…”

“…The BTS is the third largest Brazilian estuary where the drainage of a catchment area over 60 × 10 3 km 2 (twice the size of Hudson River or 1.2 times larger than Weser watersheds) is vital to maintain an estuarine circulation during the dry season on the coast (Santana et al 2018). Its most important river, draining more than 90% of the catchment area, was dammed in the 1980s for flood control, urban water supply, and hydroelectricity generation, and since then, a significant part of the riverine flow, already impacted by increasingly smaller precipitation in its catchment, does not reach the bay (Genz and Lessa 2015).…”

Chronology of anthropogenic impacts reconstructed from sediment records of trace metals and Pb isotopes in Todos os Santos Bay (NE Brazil)

“…The results obtained in this study showed notable differences between sites in (Genz et al, 2006), it may also hinder the impacts of a possible reduction of the transport of suspended particulate material to the Bay. It is noteworthy that Paraguaçu is a relatively small river (annual mean discharge of 72 m 3 s -1 , Genz and Lessa, 2015) that, despite its large drainage area, drains Proterozoic, mostly crystalline rocks (Souza et al, 2004) in a large semi-arid region, and transports a relatively small amount of solids (Hatje and Barros, 2012).…”