Background information on wealth in Brazil

1. The ability to transport things by the river system. For example, for power plants, it is much cheaper to use a barge to transport a load of coal than using trucks to haul it. Also the river is like a huge highway system that people don't need to maintain (road reconstruction) and goods can be shipped directly from ports a hundred miles inland out to see to the ocean where they can go around the world.
2. Source of resources, ranging from any different species of fish to aquatic plants to fertile river sediments.
3. Large and widespread source for irrigation of farms and orchards.
4. Most power plants and factories are built near rivers since they use large amounts of water to produce electricity and many consumer goods. This usually effects the quality of the resources obtained from the river, but they are both still options.

This link explains it