Water Flow, Velocity, and Discharge Measurement and Data Collection

Your primer for collecting discharge data
with acoustic Doppler technology

Flow, velocity, and discharge data are vital for understanding how water moves through natural and manmade environments. By using specialized instruments like acoustic Doppler current profilers (ADCPs), hydrologists, engineers, and water managers collect critical data that reveal water volume, speed, and flow patterns within rivers, streams, irrigation canals, and even coastal and deep ocean waters. These data help to ensure water resources are managed efficiently, sustainably, and safely.

SonTek M9 ADCP Collecting Data

Why flow, velocity, and discharge data are essential

Collecting accurate flow, velocity, and discharge data is essential for managing water resources, predicting environmental changes, and maintaining public safety. Many organizations, from government agencies to environmental and agricultural bodies, depend on this data for critical decision-making. Applications range from river and stream monitoring to large-scale irrigation canal management, as well as coastal and offshore water studies. By tracking water movement and patterns, these entities can understand ecosystem health, allocate resources responsibly, and prepare for weather impacts.

Flood prediction and management: Monitoring flow, velocity, and discharge data in rivers and streams helps to predict potential flood conditions, allowing for proactive public safety measures.

Water allocation in agriculture: Flow, velocity, and discharge data are used to monitor water distribution in irrigation canals, optimizing water delivery for crops while avoiding waste.

Hydropower efficiency: Accurate flow, velocity, and discharge data support energy production by ensuring that hydropower plants operate optimally.

Oceanic and coastal research: ADCP velocity data are also used to monitor currents, tides, and active waterways such as ports and harbors and contribute to scientific research in physics, biology, and ecology. This research contributes to the study of coastal erosion and climate change, advancing both environmental and commercial initiatives.

Environmental health monitoring: Tracking velocity and flow in rivers and streams aids in assessing aquatic habitats, helping to protect biodiversity and water quality.

Wading measurements – Proven method for
collecting discharge measurements

For decades, water managers have relied on technicians collecting wading measurements to get estimates of discharge in rivers, streams, and other open channels. While there are many types of instruments that can be used to collect wading discharge measurements, they all use the same basic principles. In order to calculate discharge from a wading measurement, a technician will collect velocity measurements at specific points within a channel. These velocity measurements are then used to calculate the discharge within stream reaches by using established relationships between the location of velocity measurements and the measured width and depth of the channel cross-section.

The SonTek FlowTracker2 has become the industry standard for collecting wading discharge measurements due to its ability to provide accurate and precise discharge measurements with little maintenance and no calibration required.

Training resources:

FlowTracker2 Acoustic Doppler Velocimeter Video Training Series

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Basic technique for collecting
discharge data with an ADCP

In channels where the water is too deep or moving too fast to collect wading discharge measurements, users turn to ADCPs to measure discharge. ADCPs, such as the SonTek-M9 or SonTek-RS5, provide an alternative for collecting discharge measurements when wading is safe or practical.

A common approach is to take measurements by moving the ADCP across the river or stream, capturing both water velocity and depth information. The ADCP emits sound pulses into the water, which bounce back as Doppler-shifted echoes from particles in the water. These echoes allow the ADCP to measure water velocity and depth at different points. The data are processed to calculate total discharge by integrating the water flow across the channel’s width and depth.

When data precision is crucial for extreme weather monitoring and flood events, ADCPs are often the technology of choice due to their ability to provide highly accurate, high-resolution measurements of water velocity, depth, and discharge. Unlike traditional methods, which may rely on single-point measurements or estimates, ADCPs deliver a comprehensive and detailed profile of the entire water column.

This capability is particularly valuable in extreme conditions, where flow patterns can be highly variable. The robust design and advanced signal processing of instruments like the SonTek-M9 or SonTek-RS5 allow them to perform reliably in turbulent or fast-moving waters, ensuring that critical hydrological data are captured accurately even under challenging circumstances. This level of precision and adaptability makes ADCPs indispensable for real-time monitoring and decision-making during flood events or other extreme weather scenarios.

Quick guide: The Importance of Flood Monitoring >

Training resources:

Preparing for Your Measurement: Guide to Collecting Discharge Data with a SonTek ADCP

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Examining trends and providing insights
with continuous monitoring instruments

Water managers and other stakeholders often need data on flow more frequently than can be collected with instantaneous measurements. In these situations, users may look to install an instrument that can continuously monitor flow, such as the SonTek-IQ or SonTek-SL series instruments. Once installed, continuous monitoring instruments collect velocity data and calculate flow at user-defined intervals.

These data allow water managers to investigate trends and changes in flow across long periods of time that could be missed by looking at instantaneous measurements alone. If continuous monitoring instruments are connected to a datalogger with telemetry, the data can be fed into an online data portal that allows managers and stakeholders to view flow data in real time. Using this data, decision-makers can make more informed choices about water management and communicate them to stakeholders more quickly.

These instruments are designed to be installed in natural environments and manmade structures, such as irrigation canals and turnouts. Their robust build and high-quality sensors allow them to deliver ongoing flow, velocity, and discharge data, supporting long-term water management initiatives and ensuring that water resources are monitored effectively and sustainably.

Understanding your site and the need for instantaneous or continuous water data collection

These instruments are specifically designed to be installed in both natural environments and manmade structures, such as irrigation canals and turnouts. Their robust build and high-quality sensors allow them to deliver ongoing data on flow and discharge, supporting long-term water management initiatives and ensuring that water resources are monitored effectively and sustainably.

Site selection checklist

Have uniform flow across your cross-section.
Identify a straight reach of the channel.
Secure access to the site.
Avoid or remove vegetation.
Confirm specifications.

Quick guide: ADCP Site Selection Guide >

Instantaneous instruments are meant to give a snapshot of the velocity structure and discharge and are most often used to verify a rating curve and give a detailed image of the cross-section at that given moment. Continuous measurements provide less coverage in space, as they are in a fixed location, but provide continuous time-series of velocity and flow over the user-setup profiling structure. Continuous and instantaneous systems are used in tandem for more complicated flow patterns and sites where traditional stage-discharge rating curves fail (“velocity indexing”).

Training resources:

The Importance and Key Considerations of Site Selection

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SonTek is a trusted manufacturer of hydrologic instruments, providing versatile solutions for both immediate and long-term monitoring needs. For instantaneous discharge and velocity data collection, the SonTek-M9, SonTek-RS5, and FlowTracker2 are widely used by hydrologist, water managers, engineers and researchers for precise, on-the-go measurements in rivers, streams, and coastal environments.

Not sure where to start, have questions about your site, or need some advice? Our acoustics technology experts are here to help! Share your data collection needs or challenges with us, and we’ll guide you toward the best solutions. Contact us today—we're ready to assist!