Hydrography
MEA has a long history of supplying systems for hydrographic and hydrological studies.
Stream Flow
MEA's logging systems can be interfaced to a wide variety of sensors, from the most basic pulse output sensor through to the high tech serial interface units. This gives us flexibility in choosing the best sensor for your application.
Unidata's Starflow for example provides an excellent tool for measurement of flow in streams and channels. The Starflow measures the temperature, height and rate of flow of the water. Once programmed with the cross section of the water course, the unit can then calculate flow. Starflow's are available with integrated loggers and with an optional display for totalised flow.
Water Level / Depth
A number of options are available for measuring water level. The choice of which to use is governed by the type of water body being studied and the accuracy required.
Shaft encoders provide an economical means of recording water levels to accuracy's of better than 1mm. In open channels, streams etc., a stilling well must be installed to ensure that the instrument is not affected by wind or turbulence. A float installed in the stilling well rises and falls with changes in water level. A chain attached to the float wraps around a toothed wheel, which is then turned as the float rises and falls. An optical sensor on the shaft detects the rotation and generates a signal which can be fed to either an integral or external data logger. Shaft encoders can also be installed behind a V-Notch weir used to derive flow through the channel.
Hydrostatic water level sensors provide an alternative means of water level measurement. A pressure transducer installed at the bottom of a water body will respond to the weight or head and hence depth of water above it. Hydrostatic sensors are available in two forms: vented (where a vent tube connects one side of the transducer to the outside atmosphere) and unvented, the latter being more expensive. The sensors can be supplied in a variety of depth ranges and with varying cable lengths, allowing them to be used in most applications. The small size of the sensor makes them ideal for use in bore holes (piezometers).
Gas bubblers are another useful measurement device. Gas bubblers also use a pressure transducer, but rather than measuring pressure above the transducer, the sensors measure the back pressure on a column of air pumped into a thin tube. The tube is installed in the water body and the pressure which the air bubbles must achieve to escape the tube is proportional to the height of water above it. The gas bubblers employed by MEA include integrated air compressors and provide a reliable means of monitoring water level in hostile environments.
Water Quality
Sensors are available to measure most water quality parameters. Customers can choose single purpose or multipurpose sensors. Through its linkage to Canadian company RBR, MEA can supply sensors for both freshwater and saltwater use.
As an example, MEA has built systems to monitor: dissolved oxygen, pH, conductivity (EC), biological oxygen demand (BOD), turbidity, temperature.