Sustainable Water Usage and Surface Runoff Management in Lagos, Nigeria.

The exponential growth of the world population led by the geographic expansion of urban areas in developing countries has put massive pressure on natural resources especially land and water. Water supply and water scarcity remain one of the major challenges facing the industrializing world. The United Nations forecast further increase in population which, in the absence of management and policies, will inevitably put more resources at risk. Changing climatic conditions causing more frequent and intense rainfall will also affect water management systems in the vulnerable urban areas of developing countries. The goal of this study was twofold; first analyze the patterns of water consumption in the rapidly growing city of Lagos, Nigeria and use them in a System Dynamics (SD) model to make projections about future demand. The second part used remote sensing to quantify the contribution of extensive land use/cover change to urban flooding. Land use/cover dynamics over the past decade was analyzed using satellite imagery provided by Landsat Thematic Mapping (TM). Unsupervised classification was performed with false color composite using the Iterative Self-Organizing Data Analysis (ISODATA) technique in a Geographic Information Systems (GIS). The study area was divided into four different land use types during image classification: bare land, built-up area, water bodies, and vegetation. For water demand, two different scenarios of population growth including 5.5% and 2.75 % annual increase were considered. The results showed that water demand dropped by 67% of its current value when losses in distribution were reduced by 20% and population annual growth rate kept at 2.75% over the study period. Bare land and water bodies lost 1.31% and 1.61% of their current area respectively while built-up area grew by 1.11%. These changes in land use/cover changes led to a 64% increase in average surface runoff, mostly attributable to increasing surface imperviousness and the absence of an adequate urban drainage system. This paper intends to assist the authorities of the city of Lagos who adopted a master plan in 2010 as a road map to reduce to city’s vulnerability to flooding and close the gap between water demand and water supply by 2050