Wed, Mar 20, 5:07 PM (19 hours ago)

I agree with your comments about pipe sizing generally.

The big feedermains (transmission infrastructure) tend to be designed on a per-capita water use basis only (no fire flow) typically with a maximum average day usage (estimated highest use day, i.e. portion of demand is summer irrigation). The difference between absolute peak daily usage rate and max day average demand (in Calgary anyways) is covered by balancing storage out in the network.

In the big zones and for the big pipes consideration of fire protection demand is not typically relevant - we don’t envisage 1/4 of the city on fire at the same time - we rely on the fire department to keep fires localized and to extinguish them quickly so that never happens, like it use to in a very regular basis historically. Up until public fire departments began to be established in the late 19th century onward, every major city or town burnt down at least once or sometimes on multiple occasions; London, Chicago, San Francisco, Calgary and on and on.

However, as you move down into the distribution system with smaller diameter pipes, sizing based on fire protection requirements becomes increasingly relevant. This is where the oversizing that you referred to in your feedback to Russel starts to appear; that is to say, at the local neighborhood level and with the distribution pipe infrastructure that we have the developers typically provide.

By way of example, the Shaganappi Pump Station, which provides water to 1/4 of the city has backup capacity (one pump out of service) to meet average annual demand day plus fire (fire demand is negligible however because base normal demand is overwhelming large in this case). The service area for this pump station also pumps to loads and loads of incorporated balancing storage. You could actually fight a fire in this widespread service area without any pumping going in, completely relying on the storage (that is for a limited period of time, of course, but all flow and pressure requirements would be sustained and only start to degrade once the reservoir storage dropped below 50%).

The local pump station that serves Cresmont on the other hand, has to meet peak day plus fire flow (no balancing storage incorporated). This zone is about 1 1/2 square miles. The fire flow requirement is like 175% of the peak day flow. In the station there are 2 tiny pumps, 2 medium sized pumps and a massive fire pump with an alternate energy supply that is equal to or greater than all the other pumps combined in flow capacity.

As you know, when replacing pipes in Calgary the decision to replace was pretty much always based on the pipes condition, never its capacity to supply water. Up sizing due to normal water demand increase (population density increases), fire protection (increase in fire exposures and potential fire fuel (?)) or a combination of both was after the fact once replacement been predetermined due to poor condition.

The 2 to 3 square miles of the downtown core was the only place in the city where redevelopment triggered replacement of pipes due to lack of capacity. Typically 150 mm pipes were replaced by 250 mm, 300 mm and on rare occasions 400 mm pipes.

Lately rezoning that is allowing high density buildings in traditionally low density neighborhoods has triggered developer funded main replacements strictly to enhance fire protection. These networks are typically in the original township (6 by 6 square miles and close to the downtown core).

In neighborhoods that were built in the late 1950s onward, a standard grid was incorporated that had 300 mm mains on the mile, 250 mm mains on the half mile and 200 mm and 150 mm on the quarter mile and smaller. This requirement was necessary strictly for fire flow requirements and replacement due to lack of domestic supply capacity even with density increase has never been even close to a determining consideration in my experience with the city.

New feeder mains, pump stations and reservoirs are necessary for getting water to increasingly far flung locations; lots of pipe friction energy loss has to be overcome and new requirements to lift water to higher elevations that are further away. With increased density in already developed areas the flow friction loss and lifting requirements have already been built in. Reduced summer irrigation requirements can be traded off with increased demand due to higher population density to some degree. So existing large scale infrastructure can be made to service more people in my view, if the city’s footprint is restricted.

Finally, I think the current water long range plan, should be a foipp-able document and there should be a chapter on design criteria that covers stuff I’ve discussed above?

Hope this is helpful?