Tools that measure the speeds of floods are important to public safety.
Measuring the speed of floods can be difficult. The duration of flood discharge is typically only a few hours to a few days, the work is time consuming and strenuous, and gathering measurements puts human life on the line.
Still, for public safety, it is necessary to gauge the speed of floods. To do so, geologists and engineers use several tools to document the velocity of the stream on horizontals and verticals, the average surface velocity and the velocity of the width through a single cross section.
Ott-type Curent Meter
The Ott-type current meter is a torpedo-shaped instrument with a propeller. Suspended by a cable, it’s placed into the water where it will accurately measure stream flow velocity. It can measure flow speeds from 0.1 to 33 feet per second by equating the proportional rotations of the instrument’s propeller to the velocity of the water.
Surface Velocity Meters
Using a similar propeller technology as the Ott-type meter, surface velocity meters measure flood speeds with dangerous velocities. These meters are attached to rods and extended by hand from bridges, banks, or boats, in order to provide a safe immediate measurement.
If the flood current is steady and slow, engineers use a fluorometric dye to determine speed. Once the dye is put in the water at point A, an instrument at point B downstream will measure for concentrations of the dye. From this, flood speed of travel is calculated.
Acoustic Doppler Current Profiling
Acoustic Doppler current profiling needs a boat to be put in action. The Doppler instrument is dropped in the water. As the boat moves, the instrument takes measurements of depth, speed and water direction, immediately converting this data to binary data to provide real-time measurements.