Where the sewerage comes from and where it goes to, and the lie of the land. 

Dear Ian,

Thanks a million for your answer. I would be pleased if you could provide me with an answer from the "asset management" point of view.

Sewer network construction costs are dependent partially on the costs of the installed pipes, but depend more on the initial costs of trenching and back-filling. The underground plant is expensive to replace, and so it must be regarded as an asset to be carefully managed. Sadly, maintenance is usually reactive rather than proactive. Greater reliability is achieved (at greater costs) by trenching deeply. Redundancy is not used to ensure greater reliability as it is in other networks. Good record keeping and communication with other network providers ensures that they will not inadvertently damage your assets during their network repair and expansion. Toll-free numbers should be well advertised to minimise damage and repair time. Tree roots and inadvertent rain flooding cause the main problems. Depending on the area, pollutants may enter the system. 

If you were to "sell" the network to a commercial company, how much would you charge for the parts of it? These are your assets.

A municipality will typically recover their investment costs many times over in the lifetime of the network. Interestingly, as with other networks, they charge all customers of the same class the same monthly fees, irregardless of the length of the shared network actually needed to connect the customer to the processing plant. This is regarded as being "fair", and the municipality pays off its investment borrowings faster via the customers close to the processing plant. All customers in a particular class (domestic, industrial..) are regarded as being equal sources of revenue.

The other big investment goes into the processing plant, which, by necessity is placed at low points. The processing is mainly mechanical, resulting in low maintenance costs.

 I attach a reading list for you. Follow also the links to the links!

https://scholar.google.com/scholar?hl=en&q=sewer+network+assets

Combination of least cost rehabiliation and enhanced condition and performance as condition alone is not enough. Besides, risk management shall be a main concern. Also, one main thing is to know the optimum time to intervene and this could be done by optimized scheduling.

Dear Khalid,

Thank you very much for your answer. I would be grateful if you could discuss about the main performance (or criticality) indices considered (or should be) for sewer pipes' rehabilitation activities (or failure risk assessment).

Hi

Actually, it depends on your definition of criticilaty, performance and condition. You can refer to multiple researches in this field and decide which definition you are following.