Potential effects of a major navigation project (Paraguay-Paraná Hidrovía) on inundation in the Pantanal floodplains

Abstract

The Pantanal wetland of Brazil, a vast complex of seasonally inundated floodplains along the Paraguay River, is renowned for its outstanding biological resources. A proposed navigation project known as the Paraguay–Parana Waterway (or Hidrovia) would deepen the Paraguay River channel to facilitate year-round navigation through the Pantanal. The possibility of decreases in river levels (stage) has aroused concerns in relation to the potential environmental impacts, however the poor understanding of the hydrological relationships between rivers and floodplains has hampered evaluation of these impacts. The present study evaluates the potential impact of river modifications on adjacent floodplains by examining the relationship between the Paraguay River stage and the extent of floodplain inundation. Satellite observations of flooded area (from passive microwave emission; monthly data for 1979–1987) are plotted against river stage from several stations throughout the region to show the stage–inundation relationships for eight subregions along the Paraguay River. Scenarios in which the Paraguay River stage is decreased from the 20th and 80th percentile values reveal large potential impacts on inundation. For stage decreases of 0.10 and 0.25 m, the total flooded area is reduced by 1430 and 3830 km2 at low-water, and by 2410 and 5790 km2 at high-water, respectively. The floodplains of the two northernmost subregions appear to be most susceptible to reductions in flooding, losing more than half of their flooded area with a 0.25-m decrease in the low-water stage. The ecological impacts of these reductions in flooded area may be particularly severe at low water, when the few areas that typically remain flooded throughout the dry season serve as important refuges for aquatic animals. These results underscore the need for better understanding of the hydrology of the integrated river floodplain systems in the Pantanal before river channel modifications are carried out. Copyright © 1999 John Wiley & Sons, Ltd.