Maranhão beach systems, including the human impact on São Luís Beaches

Abstract

The 1200 km of coastline of Maranhão is the second longest amongst Brazilian states, and is located just south of the equator between the Gurupi River and the Parnaíba Delta. Maranhão represents a transition zone from the tide-dominated Amazon-Pará coast to the more wave-dominated Ceará coast. Morphologically, this coast can be divided in three provinces: (i) Western coast – heavily indented macro-tidal coast composed of funnel-shaped, tide-dominated estuaries, separated by low mangrove-dominated peninsulas capped by dynamic barrier islands and tide-modified to tide-dominated beaches; (ii) Central coast – occupied by the four arms of the funnel-shaped, tide-dominated Maranhão Gulf, with tide-modified and tide-dominated beaches, occupying most of the more exposed outer estuarine shoreline; and (iii) Eastern coast – a relatively straight coast with tides decreasing towards the east from 7 to 3 m, resulting in wave-dominated beaches backed by extensive Holocene and Pleistocene trasgressive dune fields. In the Central Maranhão Gulf is São Luís, the most urbanized zone on the Maranhão coast. Its tide-modified beaches present many beach hazards to the beachgoers. In addition, the beach quality, considering natural (climatic, morphodynamic, and hydrological processes) and social (occupation of the land and types of services and infrastructure) conditions has been adversely affected in different ways. Local beaches are being increasingly occupied by urban development, which is affecting the equilibrium of depositional systems, primarily through the occupation of dunes and cliffs. In addition, the local water quality has been affected by the lack of an adequate public sanitation system and the presence of numerous illegal sewers, which contribute to the elevated bacteriological contamination. The lack of local urban planning has caused serious social and environmental problems and effective management plans for this sector of the Amazon coast are urgently needed.