On marine winds, waves and swells over West African coast for effective coastal management - a case study of Victoria Island beach in Nigeria

The continuous erosion, perennial ocean surges and associated flooding along most low lying West Africa coast, especially the Nigeria coast, as a result of the wave energy and its pounding effect, particularly when they are of plunging type are of great concern to the region. The Victoria Island beach in Lagos, Nigeria is of particular interest in this study. Analysis of observed winds at the marine meteorological stations over West Africa suggest that the southwesterly winds are the prevailing (more frequent) and predominant in strength during the rainy season (April-September). The coastal winds generally lie between 210-250° in direction and have a mean velocity of about 10 knots. Preliminary investigations into the nature and characteristics of the marine winds, generated waves and the corresponding coastal swells for the rainy months of 1999-2001 were carried out using a parametric wave model. It revealed that winds from the fetch area (lat. 10°S-20°S and long. 10°E-20°W) generally increase from East to West with their strengths, lying between 6-18 kts. The winds were observed to be weak in August while July and part of September presented much stronger winds. The corresponding wave heights generated at the front edge of the fetch area were not less than 0.3m and not more than 2.8m, with the period ranging between 2.8 and 6.5sec. Further investigations revealed that it takes the lowest generated wave about 5-8 days and the highest about 2-3 days to reach the coast as swells. Also, between 1999 and 2001, coastal swells were rarely more than 2 m in height. However, during the high spring tide, swell height could exceed 2.5 m and coincides with observed ocean surges. The study also showed that higher waves were more frequent in 2000 than 1999 and 2001. With the perennial wave effects over the coast, some remedial measures including assessment of the coastal resources and processes, capacity building and enlightenment, institutional arrangements and coastal conservation policies are being discussed.