Bathymetry is that collection of water depth data that gives us an idea of how far down the water column extends to the sea floor, similar to elevation values for land topography. A bathymetric map is typically coloured to show classes of depth, so users can easily figure out deep or shallow areas, as well as shapes of the sea floor (bathymetric data uses).
A single point of bathymetric data consists of a coordinate with depth value relative to mean sea level. Bathymetric data can be obtained from nautical charts (special-theme maps) such as the UK’s British Admiralty Bathymetric Charts (UKHO), as well as from field collection using a sonar depth gauge with Global Positioning System (GPS). For our projects, the finer-scale bathymetry required of inshore areas was field-collected to improve on the resolution of the Admiralty data. Equipment included an echo-sounder and Trimble Garmin GPS. Depth (vertical datum) was then post-processed by calculating the water height at mean sea level according to the tidal elevation differences for each hour of depth measurement. The depth of the Portland Bight, Kingston Harbour and the Port Royal Cays shelf area is relatively shallow (20 m – 30 m depth at maximum). Bathymetric data was input for the area from Kingston Harbour to Portland Bight. Grids were generated as triangular elements (shown below). The minimum (coastal region) and maximum (open boundary) grid spacings were drawn ranging from 250 m to 2,000 m, respectively, and at least 2 vertical layers were built from the surface to the bottom.