Washington, August 13 : Environmental activists in Brazil have warned that the combined impacts of numerous small hydroelectric dams in one river basin can be at least as harmful as one large dam.
According to a report in ENN (Environmental News Network), the warning is a result of a flood of new projects along the rivers of the western Brazilian state of Mato Grosso.
"Hydraulic energy from small dams is interesting because of its low environmental costs, but everything has its limits," said Andre Villas-Boas in reference to their proliferation along the tributaries of the XingA River, in the Amazon.
At least six small dams are concentrated on the rivers in northeast Mato Grosso, points out Villas-Boas, coordinator of the XingA Programme of the non-governmental Socio-Environmental Institute (ISA).
Two have already been built and a third has been given the green light by the energy and environmental authorities for the Culuene River alone, the main tributary of the XingA.
According to Villas-Boas, such projects should not be authorized without an integral assessment of the river basin in its environmental and social aspects, for a planned exploitation of the water resource as a whole, and limits on the number of hydroelectric dams.
Often included among "clean" sources of energy, small hydroelectric dams have become an attractive business for the "soft legislation" under fiscal and financial control and incentives, without duly considering that "they seriously alter biological dynamics" if there are many in one watershed, he said.
There have been several cases where indigenous people have taken government officials or construction company employees hostage, in a bid to bring the work on dams on the Juruena and the Culuene rivers to a halt.
In other efforts, lawyers have tried to do so through legal channels, obtaining temporary suspensions of construction permits. "We predict that there will be fewer fish as a result of the energy projects on local rivers, begun around 10 years ago, because the dams block the fish from swimming upriver to breed," said Paulo, a member of a tribe that lives in the XingA Park.
"The affected rivers, which are already polluted by agro-chemical runoff, flow towards the Park where they form the XingA River, and as a result the problems will be aggravated," he said, adding that it is essential to mobilise indigenous communities to raise awareness about the threats.
According to Juarez Pezzuti, a biologist who conducted a study of the effects of Paranatinga II, a small hydroelectric dam operating on the Culuene, the dams reduce the quantity of fish in the rivers because they alter currents and nutrition, in addition to eliminating migratory species.
Attempts to reestablish reproduction have not been successful.