Impacts of a large hydroelectric dam on the Madeira River (Brazil) on floodplain avifauna

ABSTRACT Hydroelectric dams represent an important threat to seasonally flooded environments in the Amazon basin. We aimed to evaluate how a dam in the Madeira River, one of the largest tributaries of the Amazonas River, affected floodplain avifauna. Bird occurrence was recorded through simultaneous passive acoustic monitoring in early successional vegetation and floodplain forest downstream from the dam and upstream in sites impacted by permanent flooding after dam reservoir filling. Species were identified through manual inspection and semi-automated classification of the recordings. To assess the similarity in vegetation between downstream and upstream sites, we used Landsat TM/ETM+ composite images from before (2009-2011) and after (2016-2018) reservoir filling. Downstream and upstream floodplain forest sites were similar before, but not after dam construction. Early successional vegetation sites were already different before dam construction. We recorded 195 bird species. While species richness did not differ between upstream and downstream sites, species composition differed significantly. Ten species were indicators of early successional vegetation upstream, and four downstream. Ten species were indicators of floodplain forest upstream, and 31 downstream. Seven of 24 floodplain specialist species were detected by the semi-automated classification only upstream. While we found some bird species characteristic of early successional vegetation in the upstream sites, we did not find most species characteristic of tall floodplain forest. Predominantly carnivorous, insectivorous, and nectarivorous species appear to have been replaced by generalist and widely distributed species.

Effects of the Belo Monte hydro-electric-dam complex on crocodilians in the Xingu River, Brazilian Amazonia

The Belo Monte hydroelectric dam on the Xingu River has the third largest generating capacity of any hydroelectric dam in the world. We conducted surveys of crocodilians (Caiman crocodilus, Paleosuchus trigonatus) by boat in the Xingu River at the site of the dam prior to (2013-2015), and after filling (2016-2017). While the number of C. crocodilus sighted decreased with increasing water level, there was no difference in numbers prior to, and after reservoir filling. The number of P. trigonatus was unaffected by both water level prior to and after reservoir filling. Reservoir filling had little effect on the number of crocodilians using the forest around the Xingu River reservoir. Most crocodilians seen in forest surveys were P. trigonatus, both before and after reservoir filling, but C. crocodilus was recorded occasionally in the forest. It seems that most Amazonian crocodilians are sufficiently generalist to adapt to the new conditions created by the construction of dams, at least in the short-term. However, there may be long-term collateral effects on crocodilian populations from dams, due to as deforestation and improved access for hunters.

Amazonian run-of-river dam reservoir impacts underestimated: Evidence from a Before-After Control-Impact study of freshwater turtle nesting areas

1. Although the construction of hydropower dams is widely assumed to generate myriad negative impacts on biodiversity there remains a lack of robust scientific evidence documenting the magnitude of these impacts particularly across highly biodiverse tropical waterways. Hydropower expansion is an increasing threat to the Endangered yellow-spotted river turtle (Podocnemis unifilis) across its tropical South American range. 2. Turtle nesting-areas were monitored as an indicator of dry-season river level changes following run-of-river dam reservoir filling. A Before-After-Control-Impact (BACI) study design was established with multi-year field campaigns monitoring turtle nesting-areas along 66 km of river upstream of the dam, separated into 33 km control and impact zones. 3. The cause and extent of changes in nesting-areas was established using Generalized Additive Models. Nesting-area density was examined in relation to four variables: Before-After, Control-Impact, distance to the dam and precipitation. The extent of changes was examined by comparing the proportion of nesting-areas remaining in subzones during the four years after reservoir filling. 4. Comparison of the proportion of nesting-areas remaining after dam construction showed that a permanent dry season river level rise extended more than 20 km beyond impact assessment limits. On average the density of nesting-areas declined 69% (from 0.48 to 0.15 per km) across 33 km of river directly impacted by the dam. This loss was reflected in a significant BACI interaction. The variation in nesting-areas was not explained by seasonal precipitation, whilst nesting-area density increased significantly further away from the dam. 5. Standardized monitoring of freshwater turtle nesting-areas provided an effective means to quantify impacts of hydropower developments across biodiverse yet rapidly changing waterways. The negative impacts should be preventable by mitigation actions including habitat restoration and dry season flow regulation. Such measures are also likely to benefit multiple species in highly diverse Amazonian rivers increasingly impacted by run-of-river dams.

Deformations on a Talings Dam Embankment Due to Its Heightening and Reservoir Filling

The purpose of this article is to evaluate the deformations of a compacted embankment dam, partially supported on tailings, through the use of two-dimensional and three-dimensional finite element models using PLAXIS® and TOCHNOG® software, respectively. The modeling was developed to simulate the construction of a complete dam stage, with a compacted embankment, a launched embankment platform, and the filling of the dam reservoir with the tailings. The material deformation parameters were calibrated so that the numerical modeling results are consistent with the data obtained from the instrumentation installed on the dam. The results made it possible to represent and understand the deformation mechanisms that occur during the construction of a raised stage and the filling of the reservoir.

A procedure to forecast and manage water resources and to redistribute runoff water flow when passing floods

Economic losses from floods have become catastrophic due to the increase in the number and scale of their propagation. Existing procedures for passing floods and pre-preparing reservoirs for flood water acceptance are ineffective and need to be improved. Therefore, the task to devise a methodology that would eliminate these shortcomings was urgent. This paper has proposed a procedure for calculating the passage of floods based on the forecasts of water inflow, taking into consideration the characteristics of the flood wave and the mode of reservoir filling, which makes it possible to bring down (reduce) the maximum flow rate through a waterworks by accumulating floodwaters in the reservoir. The software package Mike 11 (Danish Institute, Denmark) was employed to build a hydrodynamic model of floodwater movement along the examined river section from a hydrological station to a waterworks, which makes it possible to determine the levels of water and the flow rate in a reservoir at any time in the form of free surface curves when passing floods of various range. Based on the devised methodology, recommendations have been compiled for the forced discharges of water through hydroelectric turbines (in m3/s) when passing floods of various probabilities (which is especially important for floods whose probability is 0.01 %). The constructed hydrodynamic model of floodwater movement through a reservoir has allowed the verification of the devised procedure. The procedure was devised in order to effectively pass floodwaters and bring down the maximum flow rate through a waterworks. The introduction of the methodology for calculating the passage of floods could make it possible to avoid idle water discharge through the water drains of waterworks to the lower pool and provide for the most efficient utilization of floodwater resources

Effect of Grand Ethiopian Renaissance Dam on the Water Footprint of Aswan High Dam Hydropower

Construction of the Ethiopian Grand Renaissance dam (GRD) has many impacts and implication on the water share and future use in Egypt. Especially the period of the reservoir filling will have a great effect on the Nile River and its water in Egypt. Many of these effects of the GRD on Egypt has been studied before, but no study was done on the effect of its existence on the hydropower water footprint of the High Aswan dam. This research is concerned by simulating the effect of the different GRD reservoir filling scenarios on the water footprint of the hydropower generated from the High Aswan dam. Also, the effect on the hydropower of the Aswan dam itself is also simulated and assessed. Mathematical modeling is used to reach those goals. Three filling scenarios of the GRD were investigated: namely 3 years, 5 years, and 6 years. It was found that as the filling duration of the GRD decreases the negative effect on the hydropower water footprint increases.