A critical component of studying how waves and currents move sediment in shallow, nearshore waters is the knowledge of the bathymetry or underwater depth. This is true for studies on open coast sandy beaches where surf zone dynamics drive the system, inlet environments where bathymetric evolution can rapidly change navigation channels, and in more benign, lower-energy coastal environments that evolve slowly over years to decades.
Difficulties in obtaining shallow bathymetry where waves break and submerged hazards are present has led to the development of survey systems on highly maneuverable personal watercraft such as the Yamaha Waverunner. Known as the Coastal Bathymetry Survey System or CBASS, the Waverunner is equipped with differential GPS, a single-beam 192 kilohertz acoustic echo-sounder, and an onboard navigation system. Accuracies in estimating water depths using the CBASS are in the 0.07-0.10 meter range. The high maneuverability of the CBASS makes very shallow water bathymetric surveys possible with acoustic altimeters, particularly in regions where larger vessels cannot operate or where repeated high-resolution surveys are required.
The CBASS is a well-tested survey tool in shallow marine and fresh water systems. The craft is rugged and reliable in the surf zone, and has been proven to work well in rocky, hazardous waters when appropriate caution and operator experience is taken into consideration. The utility of using CBASS in shallow water environments has heightened interest in incorporating other measurement capabilities, including those provided by multibeam echosounders for measuring fine-scale seabed topography, acoustic Doppler current meters, and undersea video cameras.
For more information on CBASS, contact Dr. Thomas Lippmann.