Abstract: One feature shared by developing countries is urban sprawl, which frequently encroaches on exclusive physical planning provisions such as the right-of-way for overhead high voltage transmission lines (HVTLs). Geospatial techniques were used in the study to assess the encroachment status of the overhead high voltage transmission lines corridor’s Right-of-Way (RoW) in Alimosho LGA, Lagos State, Nigeria. The gazetted setbacks of 15 m and 25 m for 132 kV and 330 kV HVTLs respectively from the Transmission Company of Nigeria (TCN) were used to generate the RoW extent. Topographic maps and Ikonos high-resolution imageries were used to extract the landuse and landcover (LULC) of the RoW for 1983, 2002, 2008, 2014, and 2022 at a minimum mapping unit (MMU) of 1:1,500 to assess the level of encroachment. According to the study, the HVTLs RoW has been increasingly encroached upon, 5% (1983), 57.54% (2002), 66.09% (2008), 72.56% (2014), and 82.60% (2022). Within the RoW, commercial and residential LULC are the most prevalent. Mechanic workshops, block industries, small scale trading businesses (kiosks and containers), welding workshops, and car wash sheds were also identified as dominant human activities directly beneath the 330 kV and 132 kV towers. The study concluded that there was little or no encroachment enforcement and that built-up areas around the HVTL posed health and safety risks. The study therefore recommends that the enforcement of the control laws and regulations on setbacks for HVTLs be followed strictly to discourage any further encroachment, while all existing buildings and activities on the RoW be removed.
Key words: Encroachment; GIS, Mapping, Overhead High Voltage Transmission Lines, Right-of-Way