Results of a horizontally mounted ADCP under stratified conditions

Busy channels in a sea harbour do not easily allow current measurements in real time. Acoustic flow meters based on the principle of acoustic travel time have the disadvantages of their sensitivity to horizontal and vertical current variations and large costs of installation. Nevertheless, real time data of these currents is of importance for the guidance of ships as knowledge of the currents improves safety and allows a wider time window for entering and leaving the harbour. The goal is to investigate the possibility of using data of a horizontally mounted ADCP for measuring flow velocity and direction in a stratified river or channel. Measurements were performed during one month with a horizontally mounted ADCP in a 600 m wide waterway in the Port of Rotterdam. Ten transducers produce two horizontal acoustic beams pointing from one quay to the other. In order validate the system simultaneous measurements were carried out one the one hand with a vessel-mounted vertical ADCP on two transects during a tidal cycle and on the other hand with a frame-mounted vertical ADCP during a month. The authors compare the horizontal ADCP data with the data of a vessel-mounted and a frame-mounted ADCP. It has been shown that the horizontal ADCP averages flow over the upper fresher and more dynamic water layer with an accuracy of 0.15 m/s. They propose a method for real-time ship guidance by computing flow velocities averaged over the upper fresh water layer from horizontal ADCP data