When a man has mastered the ability to travel by sea, he began to wonder what is the depth clearance under the keel and how to measure the depth. Initially, only coastal shipping was practiced. Cargo ship sailing, fishery, underwater scientific research, recreational diving as well as resource exploration and operation of submarine cables and pipelines laying were developing dynamically in this part of the continental shelf. That is why accurate bathymetric information was of great importance to masters, scientists, fishermen, ship-owners and all seafarers.
Cartographic compilation of even a primitive nautical chart was a huge challenge. It was a painstaking process and required, first and foremost, a large amount of data, which was primarily obtained through not efficient measurements. As technology progresses, new techniques and methods of ocean exploration have developed. The technology, systems, devices and instruments of underwater exploration have gone through a long way of change, modernization and improvements, ultimately creating the potential for a bottom surface visualization as three-dimensional spatial models. A significant role has been played by multibeam echosounder which revolutionized the hydrographic surveys and proved to be efficient means of hydrographic and oceanographic surveys.
Rivers constitute an important focus of attention in surface water studies because of their dynamic nature. Therefore, natural rivers develop a wide range of channel forms whose characteristics vary as a function of the position within the fluvial systems. This study examined the river channel morphologic parameters along the alluvial section of River Ogun in South western Nigeria. Data on the channel morphologic variables were collected through field measurement of the bankfull cross sectional characteristics of the river from where the longitudinal characteristics were defined. 48 cross sections were randomly established at bankfull stage along the river channel stretch of 90 km. Bankfull depth and width at each of the cross sections were determined using sonar (electronic sounding machine) that was mounted to a boat. Velocity was measured with the aid of a current meter, while other morphological parameters were estimated from the field data. Analysis of variance revealed that downstream morphological characteristics of the river varies distinctively at each cross section with bedslope as the most significantly varied among all other morphologic parameters (F=91.18; P=0.00). Pearson product moment correlation technique revealed that bankfull width had a correlation of 0.8 and 0.9 with wetted perimeter and cross sectional area respectively while bankfull depth (maximum) had correlations of 0.9, 0.8 and 0.78 with hydraulic radius, wetted perimeter and cross sectional area respectively. The research also revealed that gradient affects the discharge with a positive correlation of 0.9. The study ascertains the extent of variability in the morphologic characteristic of River Ogun which provides scientific basis for river maintenance and management.