Science - November 25, 2004

Brazilian river out of control

The people living along the Taquari River in the western part of Central Brazil are regularly confronted with floods. The amount of sediment that comes with the floodwater is also enormous. A Brazilian/Dutch research team led by Alterra went in search of the natural human causes of the problem, and has now taken the first steps towards setting up a river management organisation that works.

The researchers have come to the conclusion that the main cause of the problem is a natural process of river deposition in the downstream area of the Taquari. A second important cause is the changes in vegetation on the plateaus which form the hinterland of the Taquari River. A change from dry savanna (cerrado) to grassland (for livestock rearing) has changed the ground water flows and resulted in increased soil erosion. The Taquari River is faced with much more sand to deal with and has changed from a meandering river into an unstable, weaving river that quickly silts up. It has also become very unpredictable.

Project leader Dr Rob Jongman, of Alterra: ‘The most important strategy for dealing with the river will be erosion control in the upriver area, and the people are going to have to learn to adapt their ways to those of the river. This requires a management organisation. Don’t forget we are talking about an area of 80,000 square kilometers and a population of over 100,000.’

One problem is that the regional governments have no say over the Taquari River. ‘Each individual landowner along the Taquari does as he pleases. There is very little cohesion or cooperation.’ The research team has been trying to do something to improve the situation. They have organised various meetings to try and get the various parties – governments, local population and NGOs – together. Jongman is pleased with the results so far: ‘The NGOs, one of which is called Riosvivos, are now recognised by the government and we have spoken with the state departments of the Mato Grosso and the Mato Grosso do Sul regions about river management. People from the departments have visited the Netherlands and taken a course on wetlands management at RIZA, the Dutch institute for integrated freshwater management and waste water treatment. That has helped them to start working together.’

Alterra is working together with RIZA, WL/Delft Hydraulics, ITC Enschede, the engineering company Arcadis and the Brazilian agricultural institute Embrapa. The project falls under the Dutch programme Partners for Water that started in 2000. / HB