Envco – Environmental Equipment

River Flow Measurements.

Envco is now a leading service supplier of open channel flow measurements.
Envco can carry out flow gaugings on rivers and open channels of any size (up to 40m deep) using high precision Sontek equipment including the M9 and Flowtracker systems.

Envco staff are fully trained Hydrographers and their years of experience will be invaluable for your project or application.

Why measure river and open channel flow?

There are many different reasons why streams and channels need to be measured. They can include:
Water resource assessment.
Checking for losses in a system.
Hydrometric site rating.
Resource consent compliance purposes.

How is Stream Flow measured?

Stream Flow discharge is the volume of water moving down a stream or river per unit of time, commonly expressed in litres or cubic meters per second. In general, river discharge is computed by multiplying the area of water in a channel cross section by the average velocity of the water in that cross section:

Discharge = Area × Velocity

The equipment Envco uses to obtain the discharge uses Acoustic Doppler technology.
The M9 system is an Acoustic Doppler Current Profiler (ADCP). An ADCP uses the principles of the Doppler Effect to measure the velocity of water. The Doppler Effect is the phenomenon we experience when passed by a car or train that is sounding its horn. As the car or train passes, the sound of the horn seems to drop in frequency.

The ADCP uses the Doppler Effect to determine water velocity by sending a sound pulse into the water and measuring the change in frequency of that sound pulse reflected back to the ADCP by sediment or other particulates being transported in the water. The change in frequency, or Doppler Shift, that is measured by the ADCP is translated into water velocity. The sound is transmitted into the water from a transducer to the bottom of the river and receives return signals throughout the entire depth. The ADCP also uses acoustics to measure water depth by measuring the travel time of a pulse of sound to reach the river bottom at back to the ADCP.

To make a discharge measurement, the ADCP is mounted onto a board or into a small watercraft with its acoustic beams directed into the water from the water surface. The ADCP is then guided across the surface of the river to obtain measurements of velocity and depth across the channel. The river-bottom tracking capability of the ADCP acoustic beams or a Global Positioning System (GPS) is used to track the progress of the ADCP across the channel and provide channel-width measurements. Using the depth and width measurements for calculating the area and the velocity measurements, the discharge is computed by the ADCP using discharge = area × velocity, similar to the conventional current-meter method.

The ADCP has proven to be beneficial to stream gauging in several ways. The use of ADCPs has reduced the time it takes to make a discharge measurement. The ADCP allows discharge measurements to be made in some flooding conditions that were not previously possible. Lastly, the ADCP provides a detailed profile of water velocity and direction for the majority of a cross section instead of just at point locations with a mechanical current meter; this improves the discharge measurement accuracy.
Acoustic velocity meters have also been developed for making wading measurements. Envco uses the Flowtracker for this which allows for accurate wading gauging measurements in a wide variety of situations.

Clients can get Sontek equipment, training or services directly from ENVCO. An authorized Sontek YSI agent!