The PODDS model, developed by the Pennine Water Group at the University of Sheffield has been shown capable of predicting the discolouration response of distribution networks to changes in hydraulic conditions. Results highlighting the capabilities of the full model are presented in Figure 1. The model is based on the novel application of cohesive transport theory and its development has led to a step change in philosophy and perception relating to discolouration. The PODDS research projects have developed the model into a tool suitable to be readily utilised by the water industry with a high degree of confidence in the parameter dataset required to achieve accurate model simulations. Critically the work has highlighted differential rates of material accumulation (layer regeneration or asset deterioration) within water distribution networks based on water quality factors and how hydraulic regimes are operated. Additional confirmation of these findings and how this information may be best utilised, including the application to larger diameter trunk mains now remains to be resolved.

The fourth phase of this project is therefore a way for the collaborators to lead the industry in developing and producing justifiable guidelines for planning operational and maintenance strategies to manage discolouration, particulary in strategic trunk mains.

Figure 1. Example simulation results for use of full PODDS model







1. Controlled laboratory testing:
Initial trails have been conducted in a pipe loop facility (non-temperature controlled) confirming that material layers can be accumulated and subsequent discolouration generated in a laboratory based pipe loop. Issues remain over the practical applicability of these results as the system operated at 20°C and hence the biological processes involved may be considered non-representative.
Trials utilising a new temperature controlled pipe test loop facility at the University of Sheffield are now underway. This is an internationally unique facility, with the capability of fully recreating operational pressures and flows and time vary patterns within a controlled environment. The rig is comprised of 79mm internal diameter MDPE pipe, representative of pipe currently installed in the UK. The rig comprises over 600m of pipe, which can be run either as a complete length or as three independent systems. The control of a laboratory facility will be used to systematically investigate and quantify the relative impact of different potentially influencing factors and mechanisms on material accumulation rates. Only by testing influencing processes in isolation can a true appreciation of their significance be derived.
Questions that it is proposed to investigate include:
• Hydraulics:
o Is there a steady state self cleaning velocity?
o What are the effects of daily flow patterns? Does this change if a stagnation period is present?
o Is there an ultimate layer strength for plastic pipes?
• Source water effects:
o What is the effect of changing concentrations of iron, manganese and aluminium (the dominant metals species found consistently in flushing samples)
o What is the effect of pH, alkalinity, DO etc?
• Infrastructure:
o What would be the influence of introducing a length of cast iron pipe into the system?
The laboratory based studies will run throughout the programme, with details of further study to be refined on an ongoing basis through the steering group and with reference to the field results.

2. Field regeneration trials:
Field sites utilised during PODDS project trials will continue to be tested in the same manner at determined intervals. This will provide quantification of regeneration processes within live water distribution systems, capturing the complex interaction of processes and variables at each site. This data will provide:
• Confidence in the repeatability of regeneration processes in sites where conditions do not change.
• Verification of the effects quantified through idealised laboratory trials by comparison between the different sites and with respect to changes to these sites.

3. Trunk mains:
Due to the criticality and political sensitivity of trunk mains, work relating to trunk mains will be subject to change and adaptation to suit individual company policies and strategies. However, due to significant level of interest and need for practical tools relating to discolouration in trunk mains as expressed by the PODDS Water Company Consortium, the PODDS approach will continued to be developed for prediction of trunk main response to changing hydraulic conditions. Critically trials are planned to assess the regeneration of cohesive material layers responsible for discolouration incidents when mobilised. With this information strategic fiscal planning can be justified for capital or operational investment. Trials will be conducted on a site by site basis as opportunities arise within the companies of the consortia.

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