Determination of Orthometric Heights for Enhancing Built-Up Expansion in an Urban Flood Plain on Parts of Lokoja, Kogi State, Nigeria

Abstract

Elevation is crucial for determining the location of points on or beneath the Earth's surface, particularly in flood-prone areas. In Lokoja, many residents live in low-lying regions and river floodplains, attracted by natural resources and agricultural opportunities. However, this rapid urban growth often leads to flooding, which damages infrastructure, livelihoods, and public services. This study aimed to acquire coordinates, determine orthometric heights, and identify flood-prone areas to guide urban expansion. Researchers selected 234 points at 25-meter intervals and recorded Easting, Northing coordinates, and ellipsoidal heights using a South Galaxy Differential GPS, while with a benchmark of known orthometric height, orthometric heights were measured using a spirit levelling instrument. Various maps were generated using Surfer 13 and ArcGIS software, including contour, digital terrain, watershed, shaded relief, vector, and flood vulnerability maps. Findings indicated that areas with orthometric heights between 49m and 61m are especially vulnerable to flooding and unsuitable for development, posing significant risks to human safety. Development in these regions is deemed unsustainable and threatens the well-being of the local population.