Northern brazilian river deltas: River impacts versus pristine discharge

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At present we observe a basic change in the hydro-sedimentological regime of the São Francisco river mouth. The shut-off of riverine sediment transport to the coastal zone and continental shelf by constructing dams for reservoirs along the river initiates a switch of the former wave-dominated delta to an estuary. Ongoing suppression of sediment supply has produced already significant deficits in the sediment budget at the river mouth including destruction of small villages by coastal erosion. Hydro- and sediment dynamics of this basic change will be investigated in the framework of Holocene coastal evolution. To gain more insight into the principal coastal and shelf processes governing the turnover of the São Francisco delta to an estuary, actual dynamics and Holocene evolution of the pristine wave- and tide-dominated delta of the Parnaíba River, the largest delta between the Rio São Francisco and the Amazon, will be investigated. Pure estuarine conditions at the mouth of a river of the same magnitude will be studied in the tide and wave dominated estuary of the Rio Pará/Tocantins. Detailed comparative studies of hydrodynamics, sediment dynamics and late-Holocene evolution of the three river-mouth systems provide the unique opportunity to evaluate the effects of the shut-off of riverine sediment supply on coastal and shelf sedimentation in wave- and tide-dominated settings.