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178D. MUEHEoil pumping stations (Vital et al. 2006). Accordingto these authors the construction of structuresperpendicular to the beach in Macau, Caiçara doNorte and Touros accelerates the erosion. Segmentsunder erosion of the sedimentary cliffs of the BarreirasFormation are associated to a slow retreat of thecliffs and represent a risk for constructions whenlocated too close to the edge of the cliff. Occasionalswell from the Northern Hemisphere reach the coastof Ceará in the summer months triggering erosion(Melo Fo & Alves, 1993, Melo Fo et al. 1995). Thefrequency of these events may increase as a result ofclimate change, and will contribute to the generaltrend of coastline destabilization.The population in the states of Ceará andRio Grande do Norte is concentrated along the coastand represents almost 50% of the population of thesestates, with densities ranging from 50 to 200inhabitants/km 2 (Strohaecker 2008). However,almost 40% of this population is concentrated incoastal metropolitan areas, therefore only 10% isdistributed in the rest of the coastal municipalities.According to Tessler (2008), the areas withthe greatest risk of flooding are located in theParnaiba metropolitan area in the State of Piaui, inthe metropolitan region of Fortaleza in Ceará, andalong the margins of the Apodi and do CarmoRivers, between the localities of Areia Branca andMossoró in Rio Grande do Norte.On the coast of the sedimentary cliffs, theerosion is widespread and occurs almost along thewhole coastline from the south of Rio Grande doNorte along the coast of Paraíba, Pernambuco andAlagoas. The opposite is true on the coast ofSergipe, where the abundant amount of sedimentdelivered by the rivers causes about 57% of theshoreline to be in equilibrium, while 21% is undererosion (Bittencourt et al. 2006).In Paraíba State, the segments under erosionrepresents about 42% of the 140 km of beaches(Neves et al. 2006).In Pernambuco, about 30% of the beachesare under erosion. The majority are experiencingsevere erosion due to natural factors, such as coastalcirculation and sediment deficit, while man-madeinterventions often intensifies this trend (Neves &Muehe, 1995; Manso et al. 2006). The occurrence ofbeach rocks and algae in the shoreface andinnershelf increase the sediment deficit bypreventing their transport in direction to the shore.Because of the proximity of buildings, the mostcritical areas are the beaches of Boa Viagem,Piedade, Candeias and Barra das Jangadas in Recife.In Alagoas, the vulnerability to erosionis caused by the reduced delivery of fluvialsediments. Erosion is concentrated primarily on thenorthern coast of the state, where tourist activity isconcen-trated (Araújo et al. 2006). According toDominguez (1995), the susceptibility of the coast toerosion is demonstrated by active cliffs of theBarreiras group, the almost absence of coastal plainsand Pleistocene terraces as also the occurrence ofsubmerged beach rocks attesting the retreat of thecoastline.In Sergipe segments under erosion arelocated in Atalaia Nova, north of Aracaju, and to thesouth of the São Francisco River outlet, where theVila do Cabeço was completely eroded. Areas ofhigh shoreline variability are located near the outletsof the Real, Vaza Barris and Sergipe Rivers, whereerosive episodes have caused significant materialdamage (Bittencourt et al. 2006).In Bahia, the coast between Mangue Seco, atthe outlet of the São Francisco River and Salvador,is in equilibrium (Dominguez et al. 2006).According to Strohaecker (2008) based onIBGE data, the general trend of the State populationis to concentrate in coastal municipalities. Around40% to 50% in Rio Grande do Norte, Pernambucoand Alagoas, 30% to 40% in Sergipe and Bahia and20 to 30% in Paraíba. The majority lives inmetropolitan areas with only 10 % distributed alongthe remaining coastal municipalities.The areas under greatest risk to flooding(Tessler 2008) are located in low-laying areas ofJoão Pessoa and Recife, in the urban area ofAracaju, in the coastal plain north of the Vaza BarrisRiver and in the low-lying areas of Salvador.The Mixed Coast of Sedimentary Cliffs and WaveDominated DeltasThe presence of the sedimentary cliffs of theBarreiras Group is still dominant but less continuousin the south. Beach ridge plains developed in frontof the Jequitinhonha and Caravela Rivers, in Bahia,Doce River in Espirito Santo and Paraíba do SulRiver in Rio de Janeiro State (Fig. 6). The changesin the alignment of the beach ridges associated tomodifications in the longshore sediment transportindicate the occurrence of alternations in thedominium between waves generated by the tradewinds and swell waves generated by cold frontsfrom the south. Therefore the compartment islocated in a region highly susceptible tomodifications in the dominium between tropical andsubtropical climatic-oceanographic processes.In Bahia, about 60% of the coast is inequilibrium, and 26% is under erosion, with intenseerosion occurring in fluvial outlets. Sedimentretention occur in Ilhéus and in unconsolidated capesPan-American Journal of Aquatic Sciences (2010) 5(2): 173-183