Careful measurement and monitoring of streams and rivers is vital to manage water resources throughout the world. Rivers also flood so the careful measurement of river levels can help mitigate damage caused by floods. River flow measurements are calculated by hydrographers and are analysed by hydrologists and other scientists. To calculate flow, the river level is measured accurately at a certain point in the river, typically at a flume or weir which has known dimensions / has been constructed to a known standard. There are different types for different conditions, for example, a flume type generally passes sediment more easily, while a V notch type is not suitable for use in waters with lots of sediment.
The water level above the low point of the flume/weir is measured and the flow is calculated based on measurement results and the shape and size of the flume/weir. For measuring the flow of large/wide rivers, manual river gauging process is undertaken. Hydrographers record level and velocity at different depths along the slope of the river bank. From these measurements, a set of relationships is determined such that the flow at the certain point in the river can be determined based on the water level at a certain point in the river, so-called stage to flow relationship.
There are several different methods used to measure streams and rivers, and these methods will be summarized below. The
measurement of rainfalls is often associated with river measurement stations as local rainfall is a key factor especially in hills or mountainous areas.
Regular reporting of river levels to a central server allows authorities to monitor stream and river flows across a country or region and
to use that data immediately if required. For example flood alerts/flood warnings as well as longer-term analysis by hydrographers and hydrologists to manage the rivers/catchments in the long term.
The measurement methods include:
• Method 1 – a still well or still pipe with a shaft encoder with a float and beaded float line system
• Method 2 – a pressure sensor which is immersed in the stream or river
• Method 3 – the more complex pressure bubbler system which allows for a small open tube to be immersed into the stream or river with a gas pump or gas cylinder to inject small bubbles into the open tube and measure water depth by measuring the back pressure required to force bubbles out of the tube in the water.
• Method 4 – Measuring depth using Ultrasonics Doppler Instrument
• Method 5 – Measuring depth using Radar
There are many measuring methods available, but still, the most common method is shaft encoder float and wheel system. This method requires a large well or a smaller pipe to be installed on the stream, riverbank or on a bridge structure, to provide a stable, not disturbed by flow or wind, measurement environment.
A small float, a float line and a counterweight system will respond to depth/level changes in stream or river. That response causes rotation of the shaft of a wheel. Shaft rotation is measured very accurately by the optical encoder and the data is simultaneously displayed and recorded in the data logger within the instrument.
The Unidata 6541 Precision Water Level Instrument is a very accurate shaft encoder instrument. The 6541 integrates both an LED display for displaying water level instantaneously and a data logger for recording / storing water level readings as required.
When a Neon Remote Logger is added, the water level information can be transmitted over the internet to a central Neon server to allow authorities to view the data on the web in near real-time.
