Hydrographic surveys define shorelines and depths of lakes, streams, oceans, reservoirs, and other bodies of water. Sea surveying is associated with port and offshore industries and the marine environment, including measurements and marine investigations made by ship-borne personnel. In addition, accurate measurement and modelling of hydrographic information is important to control waterways boat services with existing roadway transportation services. This paper attempts an empirical analysis of hydrographic data to simulate waterway navigable route within Lagos Lagoon with a minimum under-keel clearance that must be maintained by vessel transiting a port as well as berthing. The field investigation was conducted between September 2015 and March 2016 to determine river bed topography with the deployment of DGPS receivers, Single beam SDE 28S echo sounder, speed boat, tidal observation and reduction. Hypack 2008 and Arc GIS software was used for data sorting, extraction and processing. It was observed that depth within the project area ranges between 0.0m to 14.82m when referred to the Lagos datum. Furthermore, waterway navigable chart was developed based on prevailing river bed topography along the study corridors as well as passenger ferry draught constraint. From this study, derived depths were analysed in form of graphs and charts that provides a suitable framework to support ferry transportation services within Lagos Lagoon as a complimentary mode to the dominantly depended road transportation services. Therefore, periodic hydrographic survey of the navigable routes is recommended specifically to identify possible channel accretion.

Dams are reservoirs established for different reasons. Oyan dam, Ogun State, Nigeria was established and commissioned on the 29th March 1983 to supply water to Lagos State and Abeokuta for municipal uses, with power generation potentials to support Lower Ogun Irrigation Project. However, flooding has become an annual experience of downstream communities along Ogun river especially when the Oyan dam is opened; it has really becomes remarkable since the flood events of 2012. This project investigates the level of siltation and floods menace adjoining Oyan dam and its environ. An integrated methodology of bathymetric survey, total station traversing and satellite imagery were used to acquire geospatial locations of the dam features and other details within the dam through the process of traversing, heightening and detailing. The field investigation was conducted between January 2018 and January 2020 to determine dam bed topography with the deployment of integrated approach. The collected data were processed using Hydrologic Engineering Center’s River Analysis System (HEC-RAS), HYPACK software and ArcGIS 10.6 software. The maximum and minimum depth within the dam are -4.072m and -21.588m respectively. The cross sections are represented for each 200m length of the dam. Furthermore, volumetric analysis of sediment budget was computed to be 251.7x106m3 and compared with designed reservoir capacity of 270x106m3. From the study, a loss of about 18.2x106m3 approximately 6.7% was recorded. Satellite imagery shows the rate of change within Oyan dam and its catchment area downstream based on Triangulated Irregular Network (TIN) generated from Shuttle Radar Topography Mission (SRTM) the maximum and minimum elevation in the catchment are 29m and 182m respectively. The study recommends that deepen and training of Ogun river and all adjoining drainages system within the study corridor to retain more water when peak rainfall is recorded.