Statistical evaluations of sea’s state along the Nigerian coast

Abstract

Statistical evaluation of sea’s state is essential for the design and managements of marine structures, operations, shipping and navigation security. For the purpose of coastal navigation, little to no research has been done on the state of the sea along the Nigerian coast. Understanding the local sea’s state can help to lessen the frequency of incidents brought on by ships capsizing. In order to notify users of probable areas where vessel overturning may occur, this study therefore employs the warning and prediction services system created and developed by the Indian National Centre for Ocean Information Services (INCOIS). The system bases its warning advisory on the Boat Safety Index (BSI), a newly developed index with a sufficient threshold. Furthermore, this study investigates the statistical properties of the sea’s state along the Nigerian coast, using daily significant wave height (SWH) and 10 m wind speed (u) data spanning 37 years (1980–2016). The Douglas smooth (wavelet) sea’s state classification prevailed in both cases in the sea. It occurred more in the dry season than in the rainy season. The Douglas smooth (wavelets) sea also prevailed in all months of the year except in August, when the Douglas slight sea had higher occurrences. A spatial analysis using SWH showed that Douglas calm seas are predominant in the eastern waters of the study region. The majority of the study area's waters are dominated by the Douglas smooth (wavelets) sea, which is especially prevalent in the area around Lagos Lagoon. In the western coast of the study area, the Douglas slight sea had the highest frequencies. Very low occurrences of the Douglas moderate and rough seas were observed over the research area. Additionally, a spatial analysis using u revealed that the Douglas smooth (wavelets) sea prevailed in the eastern coast of the study area. The Douglas light and moderate seas increased offshore. In the far western coast of the study location, the Douglas rough to high seas showed very rare occurrences. In all, very little or no occurrence of the Douglas rough to phenomenal seas was observed. Insignificant trends exist for the Douglas smooth (wavelets) sea over the study area. The Boat Safety Index used to evaluate the research location showed that it is considered safe for coastal sailing.