Hydrographic surveys show depths and terrain configurations of the bottoms of water bodies. Hydrographic surveys can be used for monitoring sediment changes, showing pre-dredge conditions, or even showing as-built conditions of the bottom of a water body.
Engineers use hydrographic surveys for planning and monitoring harbor and river dredging operations, and to ascertain reservoir capacities for flood control and water supply systems. Furthermore, hydrographic surveys are used to build docks, determine water depth over a certain area, for cross sections through a water channel, or to monitor erosion along beaches and coast lines.
Hydrographic surveys are usually referenced to local tidal or a vertical datum.