SonTek SL Series

Side-Looking Acoustic Doppler Velocity & Flow Monitoring

The SonTek-SL Series is a range of side-looking acoustic Doppler instruments designed for continuous measurement of water velocity, level and flow in open channels. Available in three models—the SL3000, SL1500 and SL500—the range covers applications from relatively small channels through to large rivers, canals and waterways.

Mounted horizontally from the side of a channel, the SonTek-SL measures velocity across a defined horizontal profile rather than relying on a measurement immediately adjacent to the instrument. This allows the SL to sample a representative portion of the flow while keeping the instrument accessible from the bank, channel wall, bridge structure or other suitable mounting location.

The combination of multi-cell velocity profiling, water-level measurement, internal data logging and flow computation makes the SonTek-SL particularly suited to permanent hydrological and flow-monitoring stations.

Why use a side-looking Doppler?

Side-looking installation offers several advantages for permanent monitoring applications. The instrument can be mounted from the side of the channel without requiring equipment to be installed across the channel bed, reducing installation complexity and improving access for inspection and maintenance.

By profiling velocity horizontally into the channel, the SonTek-SL can measure a larger and potentially more representative portion of the flow field than a conventional single-point velocity sensor.

Key advantages include:

• Continuous water velocity, level and discharge monitoring

• Side-looking installation with minimal obstruction to the channel

• Multi-cell horizontal velocity profiling

• Suitable for channels with changing water levels and hydraulic conditions

• Effective across a wide range of water velocities, including challenging low-velocity applications

• Integrated acoustic and pressure-based water-level measurement

• Internal data logging

• Flow computation and totalised volume

• Multiple communication and system-integration options

• Suitable for permanent monitoring and telemetry applications

• No moving parts and low routine maintenance requirements

Applications

The SonTek-SL Series is particularly suited to:

• River and stream flow monitoring

• Canals and artificial channels

• Large open-channel discharge monitoring

• Quarry and mine-water discharge

• Industrial and wastewater channels

• Irrigation and abstraction monitoring

• Hydrological monitoring stations

• Flood and drainage monitoring

• Low-velocity water measurement

• Long-term remote monitoring and telemetry systems

Index-Velocity Flow Measurement

Where continuous discharge is required, the SonTek-SL can be used as part of an index-velocity monitoring station.

The instrument measures velocity across a horizontal section of the channel while integrated level measurement records changes in water depth. Reference discharge measurements—typically collected using an ADCP or another appropriate flow-measurement method—can then be used to establish a relationship between the velocity measured by the SL and the mean velocity within the channel.

Combined with a surveyed channel cross-section and the corresponding relationship between water level and cross-sectional area, this allows continuous discharge to be calculated from the SL measurements.

The index-velocity approach is particularly useful at sites where the relationship between water level and discharge is variable or poorly defined, including backwater-affected sites, regulated channels and locations where installation of a conventional hydraulic structure such as a weir or flume is impractical.

SonTek's FlowPack software can be used to develop and manage velocity-index discharge ratings.

SonTek-SL Models

The SonTek-SL Series includes three models covering measurement ranges from 0.1 m to 120 m, allowing the instrument to be matched to channel dimensions and monitoring requirements.

SonTek-SL3000

The SL3000 is the short-range model within the series, providing a horizontal sampling range of 0.1–5 m and supporting channel widths from approximately 0.5 m.

Its short blanking distance and high-resolution velocity profiling make it particularly suited to smaller channels and applications where the instrument can be positioned relatively close to the principal flow.

The SL3000 incorporates SmartPulseHD® technology and can provide velocity profiles containing up to 128 measurement cells.

SonTek-SL1500

The SL1500 provides a horizontal sampling range of 0.2–20 m, making it a versatile option for medium to large rivers, canals and open channels.

Like the SL3000, it incorporates SmartPulseHD® technology and supports up to 128 velocity profiling cells, automatically adapting acoustic sampling to the prevailing measurement conditions.

The combination of measurement range, profiling resolution and compact side-mounted installation makes the SL1500 suitable for a wide variety of permanent hydrological and discharge-monitoring applications.

SonTek-SL500

The SL500 is the long-range model within the SonTek-SL Series, providing a horizontal sampling range of 1.5–120 m.

It is designed for large rivers, canals, estuaries, harbours and other wide waterways where representative velocity measurements are required over substantially greater distances.

The SL500 provides multi-cell velocity profiling across up to 10 cells and incorporates compass and tilt measurements. Its integrated vertical acoustic beam and pressure sensor provide water-level measurement, allowing velocity, level and discharge to be monitored within a single system.

The SL500 uses a different acoustic, communications and software architecture from the newer SL1500 and SL3000 models, and these differences should be considered alongside measurement range when selecting the most appropriate instrument.

Model Selection

Selecting the appropriate SonTek-SL depends on more than channel width alone.

Important considerations include:

• Channel width and water depth

• Expected minimum and maximum velocity

• Required horizontal measurement range

• Water-level variation

• Channel geometry

• Flow distribution and hydraulic conditions

• Potential interference from the water surface, channel bed or opposite bank

• Available mounting locations

• Power and communications requirements

• Required data output and telemetry integration

• Whether velocity-only or continuous discharge measurement is required

Flux Enviro can assist with site assessment, model selection and monitoring system design to ensure the instrument and installation arrangement are appropriate for the application.

Installation & System Integration

The SonTek-SL can operate as a standalone logging instrument or form part of a complete remote monitoring station.

Side mounting provides straightforward access to the instrument while avoiding many of the installation and maintenance challenges associated with bed-mounted sensors. Depending on the site, the SL can be installed from channel walls, bridge structures, riverbanks or dedicated mounting systems.

Flux Enviro can integrate the SonTek-SL with compatible:

• Data loggers

• Telemetry systems

• Cellular communications

• Solar and mains power systems

• Batteries and charge controllers

• Protective enclosures

• Additional environmental sensors

• Remote data platforms

Systems can be configured and tested before deployment to reduce installation and commissioning time on site.

Complete Flow Monitoring Solutions

The performance of a side-looking or index-velocity monitoring system depends on more than the instrument itself.

Sensor location, mounting position, channel geometry, acoustic conditions, flow distribution and the quality of reference measurements can all influence the resulting velocity and discharge record.

Flux Enviro can support SonTek-SL projects from initial site assessment through to equipment selection, supply, installation, configuration, channel surveying, telemetry integration, index-velocity development, commissioning and ongoing technical support.

For sites where the SonTek-SL is not the most appropriate measurement approach, we can also provide alternative solutions including SonTek-IQ systems, ADCPs, point-velocity instruments, non-contact sensors, weirs and flumes, allowing the measurement method to be selected around the hydraulic conditions and monitoring objectives of the site.

SonTek SL Series Brochure