These tidal driven movements of water can sometimes reach velocities approaching 10 knots. Local bathymetry as well as tidal volume can effect this flow tremendously. Understanding and predicting tidal currents is important to many people that use the marine environment including fishermen, yachtsmen, aqua culturists, mariners and coastal pilots. There are two types of current measurement methods. Eulerian methods employ current meters that are attached to the bottom by anchors and measure the movement of water past a fixed point.
Lagrangian methods measure flow by tracking a float position as the current carries it.
In this lab we will use the Lagrangian method with a series of floats called current drogues to track the tidal current as it enters and leaves Castine harbor. We will also utilize an Acoustic Doppler Current Profiler that is attached to the boat and measures currents by bouncing sound waves off suspended particulate matter in the water. The frequency of the reflected sound energy is affected by the movements of the particulate matter and plotted on a computer screen. Current Direction and Velocity at various depths at a single station located in the main channel. The current drogues will be set at various depths and released at the same location and time in mid channel.