| Environment
and abundance of surface water, Amazon is also home to indigenous populations (Blackman and Veit, 2018). Current estimates indicate that there are 2.7 million indigenous people, representing 350 ethnic groups who are living in more than 3000 indigenous territories (Thiede and Gray, 2020). The local population of the Xingu river of the Amazon basin are one such indigenous group of Brazil living near a part of the Xingu River (Figure 2) called the Big Bend. With the construction of the Belo Monte Dam in 2010, the Xingu River – specifically, the Big Bend portion of the river, which is revered as the ‘House of God’ by the Xingu population, has now dried up by as much as 80%. The reservoir covered about 320km2
of lowlands
and forested areas, and estimates about uprooted populations are from 20,000-25,000 (Fearnside, 2020). After construction of the dam and embankments, the filling was complete around 2016. Unfortunately, for a project of this scale, where the end-product was going to be among the largest hydropower structures ever built by humans, the indigenous people whose land and water sources were affected the most were never consulted (Langlois, 2022). Hereafter, using satellite remote sensing, we show how the Belo Monte Project has altered the water availability and quality of the Xingu River for the local Xingu population. We will also use the terms dam and reservoir interchangeably to refer to the same dam- reservoir system.
Vegetation and water cover Using the visible and near-Infrared (NIR) bands of the
Landsat satellite (missions 7 and 8), we tracked the before and after vegetation cover of the Xingu region by computing the Normalised Difference Vegetation Index (NDVI). Figure 3 shows the gradual decline of vegetation cover by about 7% from the time the Belo Monte Dam project began to the start of filling of the reservoirs. Conversely, there has been a near 2% increase in surface water cover due to the reservoir filling as detected by Landsat using the Normalized Difference Water Index (NDWI) (Figure 4). An interesting observation in using the visible and NIR band is that of the seasonal variations where we found the surface water cover to fluctuate from a high 8% during the wet season to a low 1.5%. However, we also observed the issue of local smoke and fog that often rendered Landsat data unusable by producing suspect values. This is an important issue that any water manager or end-user should be mindful of before
300 250 200 150 100 50 0
0 50 100 150 Elevation (in m) 200 250
applying satellite data at the very granular level in space and time to understand impact. There are two reservoirs comprising the Belo Monte
Project. One is essentially a run of the river reservoir created by the Pimental Dam on the Xingu River right around the Big Bend (Figure 2). The second one is the Belo Monte reservoir artificially created with a canal diversion (Figure 2). Hereafter, we will call them reservoir 1 (Pimental) and reservoir 2 (Belo Monte) in our figures and analysis where appropriate. The global-scale satellite based digital elevation model (DEM) dataset that is available from the Shuttle Radar Topography Mission (SRTM) was created before the Belo Monte Dam project began. Thus, we can use the SRTM DEM data to capture the complete bathymetry of these two reservoirs and apply them in our understanding of river regulation and storage. Often times, such DEM-based reservoir bathymetry can be quantified in terms of Area-Elevation Curve (AEC) relationship which can then be used to calculate the total amount of storage (storage change) that occurs due to a given elevation (elevation change) in the water surface (Biswas et al., 2021). Figure 5 shows the AEC of the Belo Monte reservoir (reservoir 2) created via the artificial canal to divert the Xingu River flow from the bend (Figure 2). What is evident from this AEC relationship is that the natural topography of the region can accommodate a maximum inundation extent or surface area of about 300km2
(Figure 5).
Above left: Figure 3. The trends in vegetation cover of the Xingu region as detected by Landsat satellite during the time of the Belo Monte Dam project
Above right: Figure 4. The trend in surface water cover as seen by Landsat satellite during the time of the Belo Monte Project
Below: Figure 5. Area elevation curve (AEC) derived from satellite-based SRTM DEM data for the Belo Monte Dam f (reservoir 2)
Area Elevation Curve for Belo Monte Dam
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Area (in km2
)
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