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Flow Surveys

What is a flow survey?

Flow surveys provide accurate data on how water moves through rivers, watercourses, culverts, and sewer network catchments. These surveys are essential for flood risk assessments, drainage modelling, pollution investigations, and infrastructure design. By measuring flow velocity, depth, and discharge, they build a clear picture of how river systems behave under different conditions.

Whether you’re planning a flood alleviation scheme, assessing catchment response, or gathering baseline flow data, EMS offers a full-service solution tailored to the monitoring needs of natural and engineered watercourses.

Our flow surveys provide reliable, defensible data – whether for regulatory compliance, hydraulic modelling, or project development.

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Survey design and site scoping

We begin with a thorough understanding of your site and project objectives. This includes assessing catchment characteristics, access, expected flow conditions, and the purpose of the data collection.

A tailored flow survey strategy is developed to capture the right information – whether you need data for modelling, planning consent, or post-event analysis.

Flow monitoring and data logging

We deploy high-accuracy sensors to record flow rate, velocity, and depth at intervals of a few minutes. Data is collected over several weeks to ensure a representative dataset across a range of weather and operational conditions.

Our equipment includes:

  • Area velocity probes
  • Pressure transducers
  • Ultrasonic flow meters
  • Velocity profilers
  • Bi – Directional Flow Monitoring

This allows us to monitor baseflow, stormflow, and intermittent discharges with precision.

River gauging and velocity profiling

For open channels and rivers, we perform river gauging using multiple instruments across a measured cross-section. We:

  • Measure flow depth and velocity through the water column
  • Establish cross-sectional area
  • Resolve accurate flowrates over time

Cross-sections are selected to minimise turbulence, backflow, or bed movement. Where standard methods are not feasible, we use dilution gauging as an alternative approach.

Rainfall monitoring

Rainfall plays a crucial role in interpreting river flows. We install automated rain gauges at strategic points around the catchment to record rainfall intensity and volume at high resolution.

Rainfall data is synchronised with flow data to support event analysis, model calibration, or consent assessments.

Event-based flow surveys

To capture the dynamics of specific flow events — such as storm surges, CSO spills, or flash flooding –  we deploy event-based monitoring. Equipment is triggered by:

  • Rainfall exceedance
  • River level rise
  • Flow rate thresholds
  • Manual or remote activation

This ensures key data is captured during short-duration or high-impact events that typical monitoring might miss.

Dilution gauging for complex conditions

When conventional flow measurement isn’t practical -for example, in shallow or turbulent rivers – we use dilution gauging. This involves introducing a tracer into the flow and measuring its dilution downstream to calculate discharge.

It’s ideal for small channels, culverts, and difficult-to-access locations.

Data processing and flow analysis

All flow data is quality-checked and analysed by our in-house data team. We provide detailed and summarised reports, including:

  • Daily minimum, maximum, average, and total flowrates
  • Time series graphs and hydrographs
  • Event-based discharge volumes
  • Flow duration curves and statistical summaries

We deliver data in a format ready for regulators, modellers, or planning submissions.

Remote telemetry and live data access

For sites requiring live data or rapid response, we offer telemetry-enabled flow monitoring systems. These stream data to our secure EMS portal, allowing:

  • Live access to flow data
  • Automated alerts for exceedances
  • Near real-time reporting
  • Remote system management

We also integrate data with eDAS®, our cloud-based environmental data acquisition system.

Long-term flow survey deployment

We provide fully managed long-term monitoring solutions for infrastructure development, flood risk studies, and baseline data collection. Equipment can be installed and maintained for weeks or months, depending on project needs.

All data is handled securely and reported at agreed intervals, ensuring continuity and compliance.

eDAS® data acquisition and reporting

All flow survey data can be centralised through eDAS®, our in-house environmental data platform. eDAS® provides:

  • Secure, user-friendly dashboards
  • Centralised data from multiple locations
  • Automated reporting and trend visualisation
  • Custom access for stakeholders and project teams

Frequently asked questions

Below are answers to some of the most common questions about flow surveys.

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