Back Index & Notes Next

Total Risk of Water Mains vs. Count

Summing up 30,000 valve circuits, this graph now budgets and chooses the Calgary Water Capital Replacement Programs.

Notice that the power law breaks down at high numbers here, the graph is uneven. To me, that says my model is what's wrong - if it were correctly modelling the natural phenomenon, it would be smoother on a log scale. But it's kind of irrelevant, because the job of this graph is to tell me which 98% of my valve circuits to IGNORE. I have "monitor" in quotes up there because it's a joke - whenever the United States was going to do nothing at all about civil rights in Saudi or demonstrations in Egypt, Mrs. Clinton would say "We are monitoring the situation"...which is what I'd tell people with one main break who wanted that to trigger immediate replacement. Except for being a main I'd pick for a PICA SeeSnake inspection if there were worse mains around it, "monitor" actually means "do nothing".

Above $10 per metre per year, I could borrow enough money per metre for our form of rehab, which was anodes every ten metres. Most of it was on the DI system, which has straps between mains letting current go further. Keep in mind that risk in dollars per year is the interest you can afford to pay on a capital treatment: so $20/metre would let you borrow $450 per metre for Aquapipe's lining solutions.

© Roy Brander, P.Eng 2016