Ekpa and Eyakndue, 2017 55 Nigerian Journal of Environmental Sciences and Technology (NIJEST) www.nijest.com Vol 1, No. 1 March 2017, pp 55 - 68 Determination of a Section of Woji Riverbed Depths for Safe Navigation Ekpa, A.U. 1, * and Eyakndue, N.I. 1 1 Department of Geoinformatics and Surveying, University of Uyo, Uyo, Nigeria Corresponding Author: *akwaowoekpa@uniuyo.edu.ng ABSTRACT The depths of the oceans, seas, rivers, etc. and charting the shape and topography of the ocean floor are only determined though bathymetric processes. And mariners primarily depend on water depths beneath their vessels for safe navigation. Bathymetry also goes a long way to enhance the identification of possible features on the seabed such as elevation changes, rock outcrop, wreckages, sunken vessels, pipeline, or any other obstructions that could cause hazard to navigation. This study employs the bathymetric principles to determine river-bed depths of a section of the Woji River for the purpose of creating a two-dimensional view of the underlying sub-surface and a three- dimensional model of the river-bed, to enhance safe navigation. Data acquisition was done using satellite imagery from Google Earth, total tide prediction data, sounding depths using Midas echo sounder and GPS data. Data processing performed on observed bathymetric data include spike removal, tidal correction on instantaneous depths. The processed depths were analysed and presented in form of profile view, graphs, and charts. A flow and sedimentation simulation was carried out using ArcGIS 10.3, to show the nature of the river. The tidal data aided in sounding reduction, and river average depth of 6.022m was obtained. The levelling mis-closure was 0.001m and the average variation in echo sounder calibration was 0.08m. Based on the acquired and output data, the produced chart revealed sedimentation effect on the convex coastline, uneven riverbed topography possibly due to sand excavation, which could pose serious danger to the safety of navigation. Based on these results, the use of Sub-Bottom Profiler and a Multi-Beam Echo Sounder (MBES) is therefore recommended in order to improve the quality of data obtained. Keywords: Bathymetry, chart, tidal data, navigation, mariners, accuracy, sedimentation 1.0. Introduction Seafloor mapping is one of the oldest profession known to humankind. Mariners have been measuring the depths under their vessels for thousands of years, primarily for safe navigation. Striking the rocky ocean floor would imperil the ship, threaten loss of life, and jeopardize the livelihood of those aboard. As time passed, charts derived from seafloor mapping took on a decidedly military purpose for naval warfare and were kept as closely guarded national secrets. Today, national governments, militaries, telecommunication companies, petroleum corporations, and academic institutions map the seafloor for many applications. Also, fishing activities need detailed chart in order to avoid loss of fishing gear and fishing vessels to undetected or poorly identified obstructions. They also need it to identify fishing areas where fishing is limited or prohibited (Spratt, 1989). Knowledge about our benthic habitat and seafloor is imperative as we go forward to better understand the oceans and the Earth, as this is achievable through bathymetry. Bathymetry is the science of measuring the depths of the oceans, seas, etc. and charting the shape and topography of the ocean floor (Panigrahi, 2014). Bathymetry goes a long way to enhance the identification of possible features on the seabed such as elevation changes, rock outcrop, wreckages, sunken vessels (where any exist), pipeline, or any other obstructions that could cause hazard to navigators. Recently, the instruments universally employed for this type of survey are the conventional echo sounders and swath sounding system.