Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

Abstract

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24-h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below-dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south-east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso-eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m 3 s )1 . In contrast, Taquaruçu Reservoir is relatively shallow, oligo-mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m 3 s )1 . Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above-dam site) zones of the reservoirs, as well as in the downstream river stretches (below-dam site). In both cases, the sampling was carried out at 4-h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below-dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L )1 ) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high-amplitude ⁄ low-frequency variations could negatively affect the downstream river biota.

Indirect Assessment of Sedimentation in Hydropower Dams Using MODIS Remote Sensing Images

“…However, the chlorophyll values in the aquatic systems of the Paranapanema basin are consistently low, generally around or lower than 3 µg·L −1 . This pattern has been observed for the entire reservoir cascade [42], including both storage and run-of-river reservoirs [58,59]. Even in lateral lagoons where phytoplankton development is favored, the chlorophyll values remain between 2 and 3 µg·L −1 [60].…”

Potential impact of small hydroelectric power plants on river biota: a case study on macroinvertebrates associated to basaltic knickzones

“…The disruption of the longitudinal connectivity leads fragmentation (Anderson et al, 2015), interfering with the natural downstream movement of mineral sediments (Skalak et al, 2009;Csiki and Rhoads, 2010) and distribution of particulate organic matter (Pohlon et al, 2007), nutrients (Stanley and Doyle, 2002), plant propagules (Jansson et al, 2000) and aquatic species (Benstead et al, 1999;O'Connor et al, 2006). In this way, the transference of effects should be an important ecological aspect to be considered in evaluations of impacts and cascading effects from multiple SHPs installed along a river (Naliato et al, 2009;Nogueira et al, 2012;Anderson et al, 2015).…”

Dynamics of wet‐season turbidity in relation to precipitation, discharge, and land cover in three urbanizing watersheds, Oregon

“…In the Clackamas River, shallow soil with low run‐off potential and steep topography in some parts of the basin, along with urbanization and logging, are increasing the likelihood of moderate soil erosion during intense rainfall events. A few hydroelectric dams were constructed on the river to produce energy and water supply in Clackamas and Tualatin, respectively, and the dam reservoir operating regime can promote significant differences for river turbidity and sediment concentration below the dams (De Oliveira Naliato, Nogueira, & Perbiche‐Neves, ).…”