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Originally Posted by calculoso
So, what you're saying is that the capacity of the existing sewer pipes and such don't need to be upgraded to support higher density? Seems totally counter-intuitive. Packing more people into the same space means more sewer waste going through the same pipes, which most certainly means digging up and upgrading.
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Sanitary sewer pipe sizes (the largest ones close to the end point) are going to determined by the number of people that are serviced by them, not how far away those people are from the water treatment plant. People will use the same amount of water wherever they live. However, with a spread out city, you need to build far more smaller lines out to each new community, that's where the costs add up.
Storm sewers is completely different. It makes no difference how many people are serviced by them, what matters is only the area serviced by them. The city has been building storm ponds like mad the last decade or so, even in more established areas. New communities pretty much have to be built around them (as in they have to be the first things drawn into the community plan). Why the need for so many storm ponds? Because it's virtually impossible to build large enough pipes that could handle the volume if all the stormwater from the entire city flowed directly into the river. The pipes would literally be wider than the streets they would be built under.
Water supply pipes would be similar to the sanitary sewer pipes, size would be determined by the number of people only, its the distribution network that is much larger when the city is more spread out.
As with all utilities, the cost of putting them in isn't really the size of the pipe/wire, it the length of the excavation you have to dig to put them in that makes the biggest cost difference. The equipment/labour cost is more of a factor then the material cost.