River Watch Logo
River Watch Logo

Flow Rate

Flow Rate sensors can be submersible (using pressure to calculate flow rate) or mounted above a waterbody (using water level to calculate flow rate). Flow rate sensors can detect the level of substances that can flow, like liquids, granular material and powders. The measurements produced by the sensors can help determine the number of materials within the flow of water in open channels.

How Does a Water Flow Rate Sensor Work?

Water Flow Rate sensors work by measuring the speed of flowing water. However, to measure the flow accurately, the base of the riverbed must be measured beforehand so that the volume of water can be calculated based on water level or water pressure.

What Parameters Can Indicate Water Flow Rate?

Submersible sensors use pressure to calculate the Flow Rate. Whereas sensors that can be mounted above the water use water level to calculate the Flow Rate.

Water Level Indicator

A water level indicator is a submersible sensor that relays information back to a control panel to indicate if a body of water has a high or low water level. The purpose of a water level indicator is to gauge and manage water levels.

Flow Rate Sensor Water Level Detector

Water level indicator circuits are often used in primary industries, such as forestry and farming, and industrial processes, including factories, chemical plants, and liquid systems. Uses include rainfall detection, leakage detection.

Water Pressure Indicator

Water pressure is the force or strength used to push water through pathways created by altitude or height. While water pressure often refers to water towers and city water supply, pressure changes in nature due to gravitational pull.

A submersible Flow Rate sensor uses pressure to calculate the flow. It measures the inferential flow rate based on the water’s velocity. Velocity is determined by the pressure that forces the water to move, either from the atmosphere or external factors.

Flow Rate Sensor Water Level Detector

Why is Water Flow Rate Measured?

Water Flow Rate is a commonly measured parameter, as accurate water flow data is essential for various applications. For example, climate change, pollution monitoring, and industrial water usage are just a few reasons for monitoring water flow. Changes in Flow Rate can also help understand nutrient concentration in waterways, and therefore water quality.

What Are the Different Methods of Measuring Water Flow Rate?

Before a Flow Rate sensor can produce accurate results, the river’s width must be found, along with occasionally the bankfull width. Once the width of the river and bankfull is established, the next job is to find the river’s depth at regular intervals across its width.

River Width

A tape measure can be stretched from one bank to the other at 90º. Where the dry bank meets the water, these are the start and endpoints. To avoid drag induced by the tape making contact with the flowing water and the possible increase in distance measured due to the tape stretching to a curve, it should be stretched taut roughly 20cm above water level. The ends of the measured section should be determined by observation from directly above the tape at 90º to the ground, ensuring the margin of error is kept at a minimum.

Bankfull Width

On some occasions, it is possible that a river only occupies one part of the whole channel. So, the river expands in flood conditions, and dry bank areas become part of the channel. To include a prediction of the river’s characteristics in flooding conditions, the bankfull width must be measured.

Regular Depth

The number of readings taken depends on the river’s width and the amount of detail required. Mostly, river intervals of 50cm are an ideal compromise between excessive work and loss of detail. The tape measure stretched from one bank to the other can be used as a guide to ensuring measurements are taken in a straight line, and it is also a convenient way of measuring the intervals between readings.

River Width

A tape measure can be stretched from one bank to the other at 90º. Where the dry bank meets the water, these are the start and endpoints. To avoid drag induced by the tape making contact with the flowing water and the possible increase in distance measured due to the tape stretching to a curve, it should be stretched taut roughly 20cm above water level. The ends of the measured section should be determined by observation from directly above the tape at 90º to the ground, ensuring the margin of error is kept at a minimum.

The Importance of Water Flow Rate Monitoring

Measuring water flow is vital for helping to conserve clean water for everyday uses. Consistent Flow Rate measurements can indicate changes in water quality, like an increase of nutrient levels like Nitrates. For example, a low flow rate means a high Turbidity, and a high flow rate means the water is naturally washing over the banks due to rainfall or similar.

While Flow Rate correlates with water level and pressure, it is typically an ideal indicator for excessive nutrient changes. Therefore, it provides insight into if water quality is at risk of further pollution and degradation.

New Zealand Environmental Water Quality Monitoring with Real Time Io T Artificial Intelligence Water Monitor RW

Flow Rates and Water Quality Monitoring News

The RiverWatch blog is the data centre for New Zealanders committed to monitoring and enhancing our waterways. Learn more about the water quality of New Zealand and our integral connection with the waters, and stay up to date with important news, research and developments.