Marañón River canyon

New Maps Project Potential Flooded Areas of Dams in the Marañón River basin

Friday, April 25, 2014

The majestic Marañón River, the source of the Amazon, descends from the high Andean Mountains, picking up waters from dozens of tributaries carving spectacular canyons until it reaches the flatlands of the Amazon. The Peruvian government calls it the country's "energy artery" as it plans to harness the river's hydropower potential by building more than 20 dams on the mainstem Marañón in order to power mining projects and export electricity to Brazil.

However, the Marañón River Basin is also a unique ecosystem that supplies the vast majority of the water, sediment, nutrients, and organic matter to the main-stem Amazon, fueling one of the world’s most productive floodplain ecosystems. As with many other Tropical Andes river basins, the Marañón provides the habitat and spawning grounds for many economically and ecologically important Amazonian fish species, including many that migrate from the floodplains to the foothills.  Transforming a free-flowing Marañón River into a highly fragmented, regulated hydropower cascade will cause cumulative impacts on ecosystem services provided by the basin, such as climate regulation, biodiversity, food security, and transportation among others. However, these cumulative impacts have not been fully studied or considered by developers.


Where: Marañón River basin, Perú 

Number of Dams: 22 

Reservoir sizes: These projects would cumulatively inundate 7100 sq km and over 80% of the length of the mainstem river (from the most downstream to the most upstream projects) would be flooded.

Largest Reservoir Manseriche, which could flood 5500 sq km, including natural protected areas and the communities of indigenous people such as the Awajun 

Concerns : Cumulative impacts of the projects on local and downstream people who rely on the aquatic and terrestrial resources provided by the river for food and income. Dams blocking the vast amounts of sediment, and accompanying minerals and nutrients, carried by the Marañón that support millions of fish in the Amazon Basin. Lack of protection of the region's unique biodiversity and sensitive ecosystems. Displaced communities, creating great uncertainty possibly leading to poverty.

New Resources : This study provides the first complete set of maps of potential reservoir inundation areas. However, these maps are based on historic data and point to the need for the government to release more information on its plans for the basin. 

This study pieces together historic and current information to create the first maps of the potential flooded areas caused by the dams planned for the upper mainstem Marañón River. Since the Peruvian government has not released detailed information on most of the dams, project specifications were taken from those listed in the report “Evaluación del Potencial Hidroeléctrico Nacional” written in 1968 by the German & Peruvian governments. Depending on a dated study produced large amounts of uncertainty in these map projections, but these historical data are currently the best publicly available information for most of the dams. 

The maps produced by this study illustrate the enormous scale of the development plans for the region, and point to the huge cumulative impacts these projects will have on local and downstream people and unique ecosystems. If all the planned projects were built, approximately 7100 sq km of land and river would be flooded, including many villages and towns. Over 80% of the length of the mainstem river, from the first to the last dam, would be inundated. The currently vibrant and wild river would be almost completely drowned.

Below we provide new resources for those interested in the developments on the Marañón. First, the study produced a series of large maps of the potential reservoirs :

Additionally, .shp or .kmz files are available for users who use Google Earth and geographic information systems. 

Finally, a document that outlines the data sources and methods used for this study is available to download that includes smaller maps of the individual planned reservoirs as well as additional data. 

Poster protesting Chadín 2
Poster protesting Chadín 2
Rocky Contos

The findings of this report can be updated as soon as the Peruvian government releases all studies pertaining to the Marañón mainstem cascade. There has been considerable improvement in the government’s mechanism for releasing data and we hope this continues and that enough time is granted for civil society to analyze potential impacts from hydroelectric projects. More broadly, the government must allow for open, public participation in the creation of its national energy matrix, by way of an Integrated Resource Plan for the electricity sector.