Abstract

Mapping of a small area were land and water interfaced along the coast is more economical and cost efficient with ground based approaches especially in the developing countries. Seamless Topo-Bathy demonstrated in this work is an attempt to capitalize on relatively cheap technologies available at the moment to address the challenge of providing primary data for the design of shore protection to mitigate costal erosion as well as providing chart of underwater topography for safe navigation. A total of 7,742 points were fixed with maximum depth of 9.40m achieved seaward. Three (3) potential wrecks were discovered within the study area and are mapped as they are always visible at low ebb. The Topo-Bathy map was produced with the contour interval at 0.5m. Topographic elevation was at 1.7m while bathymetric elevation was at -0.50m respectively. 1,295 tidal heights were recorded at both (H.W) and (L.W) waters.  The observed tides at the study area are basically semi-diurnal in nature, with two high waters (H.W) and two low waters (L.W) being normally repeated every 24 hours. Maximum and minimum tide heights of 0.66m and -0.97m with respect to the vertical datum. The profile of theunderwater topography for 36 cross lines starting from the  beach head with elevation ranging from +3m to 6m shows a uniform slope from the zero mark on the beachhead over a horizontal distance of 230m to an elevation of -7m. Subsequently the bed topography rises slightly to describe an underwater ridge with a bump that ranges between 1m to 2m in height. The profile then levels off to a very gentle gradient of -8m to -9m in elevation. This underwater ridge-like formation is just in front of the head of the groynes and it is thought that the groynes may have influenced its formation. The only areas without this ‘ridge like’ formation are not well pronounced, and these are found between lines 15 to 26 respectively. The TIN and the DEM was created in ArcGIS 10.3.  The TIN was created by superimposing a georeferenced imagery obtained from Google Earth with values spread between -7.34m and 9.00m. The values for the (high) and (low) were 8.99m and -9.37m respectively for DEM. It can be concluded that Topo-Bathy mapping is successful with the approach taken and is recommended especially where capital intensive methods cannot be assessed.