CaracterizaÃÃo morfo-sedimentar e evoluÃÃo de curto e mÃdio prazo das praias do Pina, Boa Viagem e Piedade, Recife / JaboatÃo dos Guararapes

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

The high rate of human occupation in the coastal area of the metropolitan region of the city of Recife since 1960, gave rise to numerous conflicts in the use and soil management, mainly due to the lack of public policies to regulate this fragile environment. This work has the objective to reach a diagnostic view of the environmental conditions of the Pina, Boa Viagem and Piedade beaches (central portion of the coastal metropolitan region of Recife), using sedimentologic, morphodynamics and hydrodynamics studies, associated with the comparative study between old and recent aerial photography. The main result was a critical analysis of the risks of coastal erosion during the last three decades. Four coastal sectors were defined based in variations in width of the beach, using ortophotocharts elaborated in 1975. Topographic profiles were conducted in all sectors, during the period from June 1996 to April 1997. These profiles evidence significant energetic variations throughout the area. The morphodynamic classification was made according to Alfredini, (1997), which relates the Dean parameter (Ω) and the declivity of beach face (tan β), giving rise to the parameter ΩTEÃRICO. The result showed close agreement with the observations from the topographic profiles. The textural parameters analyzed (average diameter, standard deviation and skew ness) favored the environmental characterization of the beaches profiles. The profile 1 showed physiographic characteristics distinct from the other profiles, having its foreshore with coarse-grained sands with good to moderate degree of selection and negative skew ness. During the study of the local hydrodynamics comparison were made between the velocity of the longitudinal currents measured in the field and those obtained by mathematic formulations (Longuet-Higgins, 1970 e CERC, 1984). This analysis showed differences in the amplitude between field and calculated velocities. Field velocities oscillated within 0,4 e 0,85 m/s, while calculated values vary from 0 (zero) to 0,93 m/s (Longuett-Higgins, 1970) and from 0 (zero) to 1,81 m/s (CERC, 1984). Similar procedure was conducted to study the longitudinal transport of sediments. The methods used to calculate the longitudinal transport of sediments were Caldwell (1956), Komar (1983) and CERC (1984). Representative values for the study area were obtained using Caldwell (1956), which showed predominance of N-S sense of transport (66%), with volumes varying from 12,81 mÂ/day to 1625,14 mÂ/day, and S-N sense of transport (34%), with volumes varying from 63,63 mÂ/day to 1313,41 mÂ/day. The data obtained throughout this work allow the identification in the two first sectors of depositional processes (low erosional risk). The sector 3 showed an increase in the erosional processes beginning in the last decade. The last sector showed moderate erosional risks and dynamic balance .

ASSUNTO(S)

praias, evoluÃÃo costeira, morfodinÃmica, sedimentologia, hidrodinÃmica geociencias beaches, coastal evolution, morphodynamics, sedimentology, hydrodynamics

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