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The Río Marañón Is Moving: Dam Construction in a Volatile Landscape

By expedition members, Alice Hill and Jaime Goode

On a tight curve on a dirt road, rock fall spat off the top of the 30-foot bank, pelting the road. By the looks of the piles of debris in the carriageway, it had been doing this for hours. Rockslides seemed to be a normal occurrence along the road to the Río Marañón in Peru’s Andean Cordillera Blanca.   This landscape is active!

Rafting down the Río Marañón.
The proposed 300 MW Rupac dam site lies at the site of an old bridge where the Río Marañón exits the inner gorge. The canyon walls can be used to buttress the impoundment while the relative openness of the valley downstream facilitates access to the site for construction. Photo: Christian Martin

We were a team of 15 – scientists, writers, a videographer, lawyer, doctor, river guides, entrepreneurs, environmental planner and energy expert – from five countries that set out to run 620 km of the Río Marañón, the headwater stem to the globally important Amazon River. Río Marañón is subject to 20 proposed dams, two of which are approved. Construction of these dams would dissect the free flowing Río Marañón into a series of pools and drops to produce energy to fuel the hungry and growing mining sector in Peru.

With the support of National Geographic’s Committee for Research and Exploration our team had two main objectives – first to document our expedition through film and photography, and second to leverage our scientific and river-running expertise to collect baseline data along the river corridor prior to dam construction. With little-to-no information currently available relating to the Río Marañón corridor, a baseline data set initiates a data record and allows for evaluating impacts after major land use or river change.

Sampling water quality.
Graduate student and hydrologist Alice Hill samples water quality on a pristine tributary in the pongos section of the Marañón. Photo: Christian Martin

In addition to challenging class II-V whitewater and towering canyon walls we found a highly erosive landscape whereby nearly every tributary catchment presented a recent sediment loading event, either through a catastrophic landslide or more simply through daily deposited sand and gravel carried in the river’s flow. The steep gradient of the Upper Marañón provides the energy to move the load. The result is massive sediment transport downstream into the jungle and the lower lying Amazon river system. What happens when a concrete blockade impedes this transport and forces the settling out of sediment in artificial reservoirs in the upper canyons instead of eventually at the Amazon Delta?

Invertebrate samples from the Río Marañón corridor.
Peruvian biologist Jorge Peralta displays invertebrate samples collected along the Río Marañón corridor between Chagual and Balsas. Despite the Marañón’s biologic importance as a feeder system to the Amazon basin, the Museo de Historia Natural (Natural History Museum) in Lima has never had the financial resources to send scientists to the Marañón. Federal funding for science and research in Peru is all but non-existent. Photo: Christian Martin

Unlike rigid dam infrastructure the people of the Marañón valley have become highly flexible to accommodate the active geologic character of the region through its oscillating dry-to-monsoon seasons for hundreds of years. Along the Marañón corridor we met an aware and educated series of subsistence farmers and communities that had very defined opinions about the future of the Marañón.   Some thought it would bring new opportunity, while most saw a future lacking sense of place, an anchored community, and a relocation plan that offered highly compromised quality of life. The river is the lifeblood that courses through the agricultural communities of the valley, and without its proximity, quality and flow the Marañón way of life would literally dry up.

Anti-dam sign.
Tupen Grande, a small riverside community, will be flooded out by the reservoir from Chadin II, an already approved hydropower dam. Most buildings and homes in Tupen Grande are used as signs like this one protesting the dam and associated nearby mega mining: “Say no to displacement (disappearance) of our towns, say no to contaminating the environment!” Photo: Christian Martin

Our expedition exited the river in the warm and humid low lying jungle, winding its way out of the valley in vehicle until the Marañón’s fickle nature presented once again. A mudslide oozed out of a small creek bed and covered the two lane road with feet of sludgy mud, blocking the road for several hours.

We walked up to the slide site passing hundreds of people waiting patiently for an opportunity to pass. An ice cream truck vendor attended a line of customers, opportunistically selling to a predictable captive market because the mudslide happens every day.   This is a way of life for the communities along the Marañón. The hillslopes fall away, roads get blocked, bulldozers arrive to scoop the mud into the river, and life adjusts. For us, it was a fitting full circle to our experience with this volatile river system. This geologic instability is cause for concern about hydropower development on the Marañón.