Hydrography is the branch of applied science which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defence, scientific research, and environmental protection.
Hydrographic surveys include sounding data (depth, position, time, and seawater characteristics) at sufficient density to depict the full detail of the seafloor accurately. The location and description of artificial and natural features such as shoals, wrecks, rocks, or coral reefs are of primary importance, affecting surface navigation.
The result of a hydrographic consultancy survey is a nautical chart: a map that shows the seafloor and other features related to navigation. Thus every hydrographic survey has four major components.
- Positioning. This refers to the location of the survey data concerning latitude and longitude.
- Water depth, measured from a vertical reference surface or datum, such as mean lower low water, to the seafloor.
- Features are sometimes referred to as targets, maybe hazards to navigation. These include wrecks, shoals, reefs, and other features.
- Seafloor characteristics. This refers primarily to the bottom type (mud, sand, bedrock, coral reef). Mariners want to know seafloor characteristics to determine good anchorages or the danger in the running aground.
Hydrographers use physical oceanography to characterize the properties of the water column, which directly impact ocean acoustics, and analyze the survey area’s tidal characteristics. Most modern surveys use acoustic soundings to determine the water depth, so a successful survey requires a solid understanding of acoustics. In addition, marine geology is useful in characterizing the seafloor. Determination of the geoid and other vertical reference levels requires geophysical data, primarily gravity. Gathering the data together and producing a nautical chart depends on sound cartography.
Benefits of hydrographic consultancy
Accurate hydrographic consultancy surveys and nautical charts yield many societal benefits.
- Safety of navigation is the single most important result of hydrography. This allows ships to safely travel in and out of ports, saving lives and property and protecting the environment.
- National Security requires that navies successfully navigate coastal waterways.
- Maritime commerce drives the global economy and depends on the safety of navigation.
- In the aftermath of a natural disaster, humanitarian relief frequently arrives on a ship. However, until a clear and safe route to shore is established by hydrographers, supplies cannot reach those in need.
- Environmental management in coastal areas depends on knowledge of changes in the marine environment. Hydrographic consultancy surveys determine changes to bathymetry and seafloor characteristics.
- Commercial fishing uses nautical charts and other hydrographic products to locate fishing grounds and navigate safely.
- Lower insurance costs. Updated nautical charting information can potentially reduce insurance costs for commercial and private shipping companies, marinas, and port and harbour authorities.
Hydrography is the science that deals with the measurement and description of the physical features of the oceans, seas, lakes, rivers, and their adjoining coastal areas, with particular reference to their use for navigation. Therefore, hydrographic consultancy is important before navigation surveys related to water bodies.