The effect of semi-aridity and damming on sedimentary dynamics in estuaries -Northeastern region of Brazil

Abstract

The estuary Basins in Ceará State are directly impacted by dams located in high and medium river courses inserted in semi-arid terrains. About 95% of the territory of the State of Ceará is dominated by the semiarid climate. Under that condition, the dams are essential, in the short term, to provide water to the population living in the hinterland and coastal zones. Over the past 10 years, dam construction near the coast has significantly increased due to more favorable rainfall (700-1500 mm) and consequently reservoirs are formed. That is te reason why the aim of this study is to evaluate the transport of bottom and suspended sediment in the estuary of the Jaguaribe, Timonha, Acaraú and Malcozinhado Rivers which carry different dimensions, hydrology and hydrodynamics, but all of them under the effect of semi-arid and damming. Due to this fact, the regional and comparative studies on geology, hydrology and freshwater flow in the estuaries have been associated to results that could be useful for the state Integrated Basin Plan. The dams reduced the inflow of freshwater tributaries during the rainy season into the Timonha, Malcozinhado, Jaguaribe and Acaraú estuaries by 83%, 75.45%, 85% and 78% respectively. In the Timonha river there was a reduction in the transport of materials to the coastal zone from 450 t to 100 t. In the Jaguaribe river around 30.000 tons of sediment are annually retained in the small lower course dams. In the estuaries of the Malcozinhado and Acaraú Rivers there was a lateral migration of the waterway causing erosions on the beaches of Águas Belas and Aranaú and damaging services and local communities.