Baseline Risk and Vulnerability Assessment

The Baseline Risk and Vulnerability Assessment (BRAVA) is an important step in the development of our DWMP in order to understand current system performance and future vulnerabilities (risks).


We screened all 381 of our wastewater catchments during the Risk Based Catchment Screening (RBCS). This flagged that 335 catchments needed to be considered further in the BRAVA stage of the DWMPs.

The BRAVA is a risk assessment for the current baseline (2020) and for future planning horizons for the 14 planning objectives. The BRAVA was completed in December 2020 for the six national planning objectives specified by Water UK. These are the objectives that all water companies are required to use in their DWMPs. We also identified two bespoke planning objectives for our DWMPs, and we worked with partner organisations to identify 6 additional planning objectives to cover issues that are important to us and our partners.

Our 14 planning objectives are:

  1. Internal Sewer Flooding Risk
  2. Pollution Risk
  3. Sewer Collapse Risk
  4. Sewer Flooding 1 in 50 year storm
  5. Storm Overflow Performance
  6. Risk of WTW Compliance (Quality)
  7. Annualised Flood Risk (Hydraulic Overload)
  8. Wastewater Treatment Works (WTW) Dry Weather Flow (DWF) Compliance
  9. Achieve Good Ecological Status / Potential
  10. Improve surface water management
  11. Secure nutrient neutrality
  12. Reduce groundwater pollution
  13. Improve bathing water quality
  14. Protect shellfish water quality

We worked with our experts and those from partner organisations to develop the risk assessment approach for the six additional objectives. We have produced a summary of the methodologies we have developed for all the risk assessments, which set out the data that we have used, the process and banding of the results. These are available to download:

BRAVA Methodology – Internal Sewer Flooding Risk

BRAVA Methodology – Pollution Risk

BRAVA Methodology – Sewer Collapse Risk

BRAVA Methodology – Sewer Flooding 1 in 50 year storm

BRAVA Methodology – Storm Overflow Performance

BRAVA Methodology – Risk of WTW Compliance (Quality)

BRAVA Methodology – Annualised Flood Risk (Hydraulic overload)

BRAVA Methodology – Wastewater Treatment Works (WTW) Dry Weather Flow (DWF) Compliance

BRAVA Methodology – Achieve Good Ecological Status / Potential

BRAVA Methodology – Improve surface water management

BRAVA Methodology – Secure nutrient neutrality

BRAVA Methodology – Reduce groundwater pollution

BRAVA Methodology – Improve bathing water quality

BRAVA Methodology – Protect shellfish water quality


The risk assessments are a first step given the timetable set by Ofwat for the first round of the DWMPs. They use the best data and information available that we held in 2020. We aim to further develop and improve the risk assessments for future DWMPs. There is uncertainty in the BRAVA results due to the modelling and data available so they are only suitable for internal use for our DWMPs.

The outputs of the BRAVA are an indicative risk score for each wastewater catchment for the current base year of 2020. For 6 of the planning objectives we have also calculated a future predicted score for 2050. The 2050 score is on the assumption that we continue with the current maintenance regime. The risk scores are either 0, 1 or 2 as described in the table below (based on the Water UK Guidance on DWMPs):

Score Description
Very Significant (Score = 2) The performance of the wastewater system is potentially below the minimum threshold set by a company, and indicates there is a risk that warrants more investigation in the Options Development & Appraisal stage of DWMP.
Moderately Significant (Score = 1) The performance of the wastewater system appears to be borderline and therefore needs further investigation in the Options Development & Appraisal stage of DWMP.
Not significant (Score = 0) The performance is not an issue or concern. Within a catchment there may be some localised issues which need to be addressed as part of ‘business as usual’ investment decisions. Priority does not need to be placed on this planning objective in the catchment.
Not Flagged Denotes that the catchment was not identified (flagged) for progression to the BRAVA stage.
Not Applicable Denotes that a planning objective is not relevant to the catchment (for example, where a catchment has no storm overflows).
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