Hydrographic Surveys in Tidal Rivers
A hydrographic survey usually consists of determination of the following types of data: topography of the bottom; heights and times of tides and water stages; location of fixed objects for survey and navigational purposes. In general a hydrographic survey means the procedure of measuring the depth of water in a river or sea utilising a boat or survey ship as a working platform while simultaneously determining the horizontal position of the boat relative to the near-by shoreline and prominent natural or man-made objects. Normally the national survey organisation, such as the Survey of India, will establish a system of bench-marks at each of its tide observation stations. Sounding is a measurement of the depth of water utilising an echo-sounder or a lead line. Surveys by echo-sounder result in a continuous line of sounding in the direction of travel of the vessel, and the variation in depth along the line is displayed in graphic form.