Groins or Not: Some environmental challenges to urban development on a Lagos coastal barrier island of Lekki Peninsula

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Worldwide, barrier islands which protect mainland areas are usually sedimentary, dynamic and in great demand for urban development. Intense development on them negates their dynamics leading to risks which necessitate protective measures such as groins which tend to aggravate the problem. Suburban Lekki Peninsula on the south of Lagos metropolis is a large, long barrier island disposed largely to unplanned, accelerated growth since the inception of Lekki Scheme 1 in 1980, all without any consideration of its physical dynamics. This study therefore assessed and evaluated some risks confronting development from the dynamics of the Peninsula with the goal of demonstrating the use of low - budget online data for analysis of coastal hazards and risks. The methodology entails the integration of remote sensing, GIS techniques to assess its characteristics and evaluate risks to development from some hazards inherent in island's physical processes as a typical barrier island on the Lagos coastline. Findings reveal that the area which was 0.5% built up in 1984 had grown to about 18% in 2014 with Eti-Osa LGA as the most developed at 68.4%. Results further confirm the Peninsula as narrow in a few sections and generally low-lying with 37% between 0.5 - 3m while 63% is between 3 - 5m above m.s.l. Eti-Osa LGA is the most low -lying of the three councils in the area with 0.5 - 3m height dominant. Medium to maximum rates of beach erosion occurs mainly in Eti-Osa LGA at about 22.75m/yr around Kuramo Waters, decreasing to 5.5m/yr around Goshen Estate. Projections on coastal erosion on the most erosive area in Eti-Osa LGA from 2013 reveal potential socio-economic impacts on road infrastructure and buildings as ranging from a minimum of N1.16billion to N139.42billion over the next 30 years at present level of development and values. The study concludes that the greatest threat and risk from barrier island processes assessed presently are mainly in Eti-Osa LGA with the old Maroko and Kuramo Waters as the epicenter. Among the recommendations toward continued occupation of the Peninsula are the base flood elevation (BFE) and design flood elevation (DFE) to enhance the resilience of future developments. Comparative observations from literature on effect of groins on down drift areas from the US were further dwelt on.