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Flow and Load Surveys

What is a Flow and Load Survey?

Flow and Load surveys are essential for understanding the hydraulic and pollutant load entering wastewater treatment works, storm tanks, and catchment areas. These studies provide water companies and public authorities with the accurate, high-resolution data needed to plan infrastructure, optimise treatment capacity, and meet regulatory requirements.

EMS delivers Flow and Load surveys for municipal and regulated utilities- from survey design and installation through to data collection, analysis, and reporting – helping you build evidence for AMP, PR24, DWMPs, and WINEP schemes.

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Feasibility assessment and scoping

We begin with a detailed assessment of your project goals, whether it’s asset planning, compliance monitoring, growth forecasting or event-based catchment assessment. Our experienced team supports you in designing a fit-for-purpose Flow and Load survey, aligned with OFWAT and Environment Agency expectations.

This stage includes consideration of rainfall dependency, seasonal variability, flow balance needs, and access requirements.

Catchment characterisation

Understanding the nature of your catchment is critical. We work with you to characterise inputs, including:

  • Population equivalents (PE)
  • Infiltration and inflow
  • Industrial contributions
  • Storm overflow activity
  • Flow splits and returns
  • Potential misconnections

Our insights ensure that the data collected reflects true operational performance and supports confident investment decisions.

Equipment specification and deployment

We deploy MCERTS-certified equipment to collect high-accuracy flow and quality data across multiple points. This includes:

  • Ultrasonic or Doppler flow meters
  • Level sensors
  • Rain gauges
  • Refrigerated auto-samplers for 24-hour composite sampling

Equipment is installed with robust mounting, battery/solar options, and remote telemetry where needed, ensuring minimal disruption and maximum data integrity.

Flow monitoring

We monitor both dry and wet weather flows using time- or event-based strategies to understand diurnal patterns, storm responses, and hydraulic loading.

Typical flow types monitored include:

  • FFT (Flow to Full Treatment)
  • DWF (Dry Weather Flow)
  • Storm overflow volumes
  • Return liquors and sidestreams
  • Infiltration contributions
  • Bi-Directional Flow Conditions

Monitoring durations can range from a few weeks to several months depending on regulatory drivers or planning needs.

Load monitoring and composite sampling

To calculate pollutant loading, our auto-samplers collect 24-hour composite samples that are representative of flow variations. These samples are analysed by  labs for:

  • BOD (Biological Oxygen Demand)
  • COD (Chemical Oxygen Demand)
  • Ammonia
  • Total suspended solids
  • Phosphorus
  • Other consented parameters as required

This data supports load profiling, treatment optimisation, and compliance forecasting.

Laboratory analysis

Composite samples collected during Flow and Load surveys are sent to UKAS-accredited laboratories for analysis. Accurate laboratory testing is critical to understanding pollutant loads and ensuring the data is suitable for compliance and planning.

Typical determinands analysed include:

  • Biochemical Oxygen Demand (BOD)

  • Chemical Oxygen Demand (COD)

  • Ammonia

  • Total Suspended Solids (TSS)

  • Total Phosphorus and Nitrogen

  • pH, conductivity, and temperature

  • Site-specific or consented parameters

All analysis follows standard methods and quality assurance procedures, with full traceability and chain-of-custody documentation provided. This ensures results are reliable, repeatable, and meet the requirements of regulatory bodies and investment cases.

Data validation and QA/QC

Our team carries out detailed data validation to ensure the integrity of results. This includes:

  • Sensor drift checks
  • Cross-verification of flow and rainfall data
  • Statistical assessment of anomalies
  • QA procedures aligned to MCERTS and WRc guidance

We ensure your data is regulator-ready and robust for planning purposes.

Regulatory reporting

We provide clear, structured reports aligned to regulatory expectations and water company templates. This includes:

  • Summary of monitoring approach
  • Flow/load data tables
  • Observations and anomalies
  • Flow balance and performance analysis
  • Recommendations for further action

Reports are suitable for submission under WINEP, PR24 business cases, DWMPs and other statutory processes.

Long-term trends and performance insights

Beyond compliance, our surveys help water companies better understand:

  • Seasonal and weather-related variations
  • Network stress points and overflow behaviour
  • Unaccounted-for flows and infiltration
  • Treatment performance against design capacity
  • Growth impact on existing infrastructure

These insights feed into resilience planning and investment strategies.

Support for WINEP, AMP and DWMPs

Flow and Load Surveys provide foundational evidence for investment planning. EMS supports projects that feed into:

  • WINEP submissions and needs statements
  • PR24 and future AMP funding cycles
  • Drainage and Wastewater Management Plans (DWMPs)
  • CSO performance tracking and strategy
  • Treatment works reconfiguration or upgrades

Frequently asked questions

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

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