Flow

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.

Key uses of discharge data


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


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


Hydropower efficiency: Accurate flow and discharge data support energy production by ensuring that hydropower plants operate at optimal efficiency levels.


Oceanic and coastal research: ADCP velocity data are also used to monitor currents, tides, active water ways 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 discharge within a section of the channel.

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. Collecting discharge data with an ADCP, such as the SonTek-M9 or SonTek-RS5, involves deploying the instrument in the water body where measurements are needed.

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 and 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 rapidly changing or 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 often 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 flow data at user-defined intervals.

This data allows water managers to investigate trends and changes in flow across long periods of time that could be missed from looking at instantaneous measurements alone. If continuous monitoring instruments are connected to a datalogger, the data can be fed into an on-line 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 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.

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

Quick guide: ADCP Site Selection Guide >

Instantaneous methods work well for quick assessments in straightforward, stable flow conditions, while continuous monitoring is better suited for sites with complex or variable flow patterns where long-term data is needed to observe trends and changes. Evaluating these site characteristics alongside your water monitoring objectives ensures the chosen method provides reliable and meaningful results.

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 hydrologists 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!