We’re still considering dams as renewable, green energy sources. While the renewable part is mostly true, that doesn’t mean that they don’t contribute to climate change, and it certainty doesn’t mean that they don’t have other negative impacts of the environment in general. In this article we’re going to focus on one of the little known consequences, coastal erosion.
When we think about beach erosion, we imagine giant machines harvesting sand from the coast, but dams also end up contributing to the degradation of coastal ecosystems. The reservoirs trap suspended matter, mainly sand and sediments that flow into them. This can significantly reduce the amount on suspended matter that reaches the lower parts of the river and ultimately the sea. When the rivers are no longer capable of replenishing the sand we witness the progressive erosion of the coast. Coastal erosion is already a massive problem in many parts of the world, and dams just make it worse.
The delta of the great river Nile is threatened by the multiple large scale dams that are harnessing its power.
“What land used to be formed in the delta in 10 years, we now lose in one year,” said Ahmed Abdel Wahab Khafaga, a government scientist trying to tackle the problem. (LAtimes)
The Nile delta is at risk both from the rising sea and from the accelerated erosion. The coastal lagoons which form a natural defense against the advancing sea are being breached. The rising sea levels are threatening 15 % of Egypt’s farmland and the livelihood of 8 million people. The salty sea water destroys the fertility of the soil in Egypt’s bread-basket. The effects of giant hydro-power installations such as the Aswan High Dam, the Merowe Dam, the Jebel Aulia Dam are felt by the millions of people who depend on the river for their survival.
“Each year, 100 million tonnes of soil erodes from the lands of Wollo and Tigre, and flows north as the Blue Nile floods. The silt raises the Nile delta by about one millimeter each each, fertilizing it and counteracting natural subsidence and erosion by the sea — that is until the Aswan Dam was completed. As well as replacing the annual flood with predictable and controllable irrigation flows, the dam also trapped 98% of the silt. Denied the fertile silt, Egypt already uses more fertilizer per hectare than any other nation. ” – encyclopedia.uia.org
The sediments that are captured by the dams don’t only affect the structure of the river and the fertility of the soil downstream, they undermine the purpose for which the dams were built in the first place :
“The proportion of a river’s total sediment load captured by a dam – known as its “trap efficiency” – approaches 100% for many projects, especially those with large reservoirs. As the sediments accumulate in the reservoir, the dam gradually loses its ability to store water for the purposes for which it was built. Every reservoir loses storage to sedimentation although the rate at which this happens varies widely. Despite more than six decades of research, sedimentation is still probably the most serious technical problem faced by the dam industry.” – internationalrivers.org
This problem is not isolated to Africa, dams are built on almost every major river in the world, and more often then not, their environmental impact has been poorly assessed.
Coastal erosion is just one of the many environmental problems caused by dams. There is an ongoing campaign lead by Patagonia against the destruction of the last European rivers, join the fight here. Moretreeslessassholes.org is doing a whole series on the subject, check out the other related articles :