The DWMP blog – Episode 17. DWMPs and asset health

This is the latest in a series of blogs discussing the development of Drainage and Wastewater Management Plans (DWMPs).?If you haven’t already seen the earlier episodes in this series, they are all here (https://tinyurl.com/MartinOsborneArticles).?I suggest that you start from Episode?1 (https://tinyurl.com/DWMP-blog).

In this episode I consider how DWMPs deal with asset health, that is the ability of drainage and wastewater assets to continue to perform their function as they age and deteriorate.?What has been the historical approach to this??What does the published DWMP guidance say??What is the best approach?

Which assets are in scope?

DWMPs are intended to cover the entire drainage and wastewater system; that is sewers, pumping stations, overflows and effluent treatment works.?They explicitly exclude the treatment of wastewater sludge.?So, the assets that should be assessed for ongoing performance should include sewers, electrical and mechanical assets in the sewerage network such as pumps and screens and all of the electrical and mechanical assets at treatment works.

How do these assets fail and what is the impact of such failure?

·????????Sewer collapses mostly cause disruption due to holes in roads and the need to carry out expensive repairs.?

·????????Sewer blockages with solids and fat cause pollution from sewage discharged to watercourses or flooding of properties.

·????????Pumps and screens in the network or at treatment works can block with solids or suffer mechanical or electrical failure leading to sewage discharge or flooding.

·????????Failure of other assets at treatment works can lead to inadequate treatment or excessive maintenance costs.

Historical background

The first area of asset health to have published guidance in the UK was sewer collapses following a spate of major collapses in the 1970s and 80s.?This led to the Sewerage Rehabilitation Manual, which recommended an integrated approach to sewer capacity and sewer collapses.?However even from day one the two studies tended to be done separately but in parallel with both contributing to a Drainage Area Plan (DAP).?

There was then a trend to carry out assessment of prevention of sewer collapses as a standalone region wide study and interface with studies of sewer capacity when required.

As flooding due to inadequate capacity was resolved the problem of flooding due to blockages became more significant and again was initially addressed as part of an integrated DAP but again the trend was to region wide programmes.?The 2010 UKWIR report Economic Level of Service for Sewer Blockages set out what was then seen to be best practice.

Asset health of mechanical and electrical equipment was generally dealt with as a regional programme.?Best practice for assessing these assets was set out in the UKWIR Common Framework in 2002 and within a few years most companies had robust decision support tools to drive these programmes. ?The surveys carried out for DASs often identified faulty assets, but getting then into the repair programme could be a challenge

DWMP guidance

The guidance published for the first cycle of DWMPs did not even mention the issue of failure of mechanical and electrical assets in the network or at treatment works.?Even if the recommendation was to follow other guidance such as the Common Framework there should have been some reference to what remains a significant issue.?Within the last week a fine was yet again imposed on a UK water company following sewage discharge when duty and standby pumps at a pumping station both failed.?

Sewer collapses and blockages were covered in the DWMP guidance but with a recommendation that “current planning approaches to risk assessment and option development and appraisal are to be continued”.?Those current approaches would generally be a regional assessment of risks and local mitigation measures.

However, the guidance does cause some confusion by including blockages and collapses in the assessment of whether a DWMP is needed but then reverting back to the current management approach for implementation.

The future

How should DWMPs deal with asset health?

I think that the two strands of asset capacity and asset health should be carried out separately but with interfaces between them.?Those interfaces would include:

·????????Capital maintenance planning for pumping stations and treatment works should identify when substantial expenditure is required on asset renewal.?The capacity assessment process should then consider whether the assets should be abandoned or increased in capacity instead of like for like renewal.

·????????Conversely the capacity assessment should identify when investment in increased capacity is required at treatment works and pumping stations and the capital maintenance plan should assess reducing major expenditure in advance of this work.

·????????For sewer collapses, the rehabilitation plan should identify any sewers that require substantial work to reduce the probability of sewer collapse.?The capacity assessment should then consider whether upsizing or re-routing of the sewer should be carried out instead.

·????????When the capacity assessment identifies sewers to be upsized then the rehabilitation programme should consider any additional benefits by extending the work to include adjacent sewers in poor condition.

·????????For sewer blockages the planned cleansing programme should identify those sewers that are likely to have ongoing reduced capacity because of repeating blockage problems.?This should be included in the capacity assessment.?It should also identify those problems that cannot be managed by routing cleansing that need the sewers to be modified.?

·????????The capacity plan should ensure that changes to the system will minimise future problems of sedimentation and blockage and should notify the cleansing programme of any increased or reduced risk of blockage from proposed system changes.

These interactions will generally occur at the start and end of developing, reviewing or revising a DWMP.?In addition, the DWMP process will generally generate a large amount of survey data including asset condition and performance.?As soon as it is obtained this should be fed into the maintenance planning process and acted on.

This partial separate will significantly simplify the confused early stages of the DWMP process.?UKWIR has this week announced a new framework for asset management for water company assets.?I hope that it has a strong interface with DWMPs.