Northern brazilian river deltas: River impacts versus pristine discharge

目前，我们观察到<s:1>奥弗朗西斯科河口的水文沉积制度发生了基本变化。沿河修建水库阻断了河流向海岸带和大陆架的泥沙输送，使以前以波浪为主的三角洲转变为河口。对泥沙供应的持续抑制已经造成了河口泥沙收支的严重赤字，包括海岸侵蚀对小村庄的破坏。本文将在全新世海岸演化的框架下研究这一基本变化的水文和泥沙动力学。为了更深入地了解控制<s:1>奥弗朗西斯科三角洲向河口转变的主要海岸和陆架过程，将研究<s:1>奥弗朗西斯科三角洲与亚马逊河之间最大的三角洲Parnaíba河的原始波浪和潮汐主导三角洲的实际动力学和全新世演化。将在里约热内卢par<s:1> /Tocantins的潮汐和波浪主导的河口研究相同大小的河口的纯河口条件。对三个河口水系的水动力学、沉积动力学和晚全新世演化的详细对比研究，为评估在波浪和潮汐主导的环境中河流沉积物供应的切断对海岸和陆架沉积的影响提供了独特的机会。

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.