Large dams | Quantifying impacts
Research into large dams has recently focused on the extent of local energy benefits for communities surrounding hydropower projects, as well as their impact on the aquatic food web
References
María Alejandra García, Adam Mayer, Igor Cavallini Johansen, Maria Claudia Lope, and Emilio F. Moran. Spatial injustice to energy access in the shadow of hydropower in Brazil. World Development 178 (2024) 10657
https://doi.org/10.1016/j. worlddev.2024.106570
Roussel J-M, Fraisse S, De´ zerald O, Fovet O, Pannard A, Rodriguez- Perez H, Crave A, Gorzerino C, Poupelin M, Forget G, Huteau D, Thomas A, Cheve´ M, Soissons L and Piscart C (2024) Effects of large dams on the aquatic food web along a coastal stream with high sediment loads. Front. Ecol. Evol. 11:1250892.
https://www.frontiersin. org/journals/ecology-and- evolution/articles/10.3389/ fevo.2023.1250892/full
RESEARCH ON THE IMPACT of hydroelectric projects on local energy services is described as being sparse, and a new study by Garcia et al published in World Development has tried to rectify this. In their investigations, the authors focused upon two dams in the Brazilian Amazon and whether they’ve had a positive impact on energy sources, access, and electricity prices for households in communities near the construction sites.
Below: The proportion of households reporting changes in energy prices after the Santo Antônio and Jirau hydropower dam construction (Source Garcia et al World Development 178 (2024) 10657)
While it could be assumed that dams would enhance energy services for host communities, the authors claim that the reality can be quite different. They go on to discuss spatial injustice in energy access, and how communities situated in rural areas far from urban centres, and lacking significant political and economic influence, often don’t benefit from any advantages of hydroelectric dam projects. Energy benefits tend to accrue to urban centres and industries, leaving communities near dams with costly and polluting diesel generators, they claim. The authors used survey data from households in communities surrounding the Jirau and Santo Antônio dams on the Madeira River in the Brazilian Amazon, along with geospatial analysis. It was found that households adversely affected by construction, particularly those in distant upstream and downstream communities, those who were not resettled, and those who did not engage directly in negotiations with dam builders, were less likely to experience improvements in energy access and sources. Most of these households perceived that their energy prices increased after the construction. “Our study implies that hydroelectric dams do not consistently improve energy access in nearby communities and, in fact, contribute to the persistence of spatial injustices,” the authors stated.
However, households within the reservoir communities, which include resettled communities, reported more benefits in energy access, believing their electricity access had improved, and they relied on the transmission line. The authors add that such results “confirm the idea that most distant communities to dams are less likely to receive the benefits, even though they are impacted, whether downstream or upstream”. Garcier et al concluded that more research should be carried out to assess how far from dams communities perceive these impacts. They say that dam builders must find ways to improve energy access and lower energy costs for households that are impacted by dams, regardless of their distance to the construction site and whether they are upstream or downstream. While authorities need to include these communities in their compensation schemes or distribution of benefits despite not being resettled.
Aquatic food web Other research has focused on the effects of large
dams on aquatic food webs. As Roussel et al explained in their paper, published in Frontiers in Ecology and Evolution, barriers to river flow can increase water residence time, and sediment and nutrient retention in reservoirs worldwide, potentially altering the balance in downstream food webs. The authors explored this issue on the Sélune River in Normandy, France, which is an 85km stream discharging into the Mont Saint-Michel Bay. Agriculture is a dominant activity in the catchment, and annual rainfall and erosion result in high quantities of suspended sediment and dissolved nutrients reaching the river. The river had been impounded by two 16m and 36m high hydropower dams in its lower part for a century, resulting in two consecutive reservoirs that covered 19 km of the initial river course. As anticipated, data and samples collected between 2015 and 2017 showed that the two reservoirs significantly retained sediments, phosphates and silicates, with much lower concentrations downstream of the reservoirs. There were no large tributaries flowing into the reservoirs, nor was there a specific land use pattern in the vicinity of the reservoirs, that could have influenced water discharge and dissolved nutrients. The two dams have since been removed with dismantling operations completed by early 2023, and the downstream transfer of sediment and solutes being restored after a century of disruption. The authors say that profound impacts on the river ecosystem are expected from now, and their results will help understand how nutrients and carbon flow in food webs, and how this will change during the river restoration process.
42 | September 2024 |
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