(01-10-2025, 10:00 PM)Goose Wrote: (01-10-2025, 07:59 PM)jacket3ree Wrote: This is exactly right. I've designed municipal water systems for nearly 40 years and we do not design them with massive wildfires in mind. Those are natural disaster, Force Majure, Act of God scenarios (even if god is an electric company) and no one can afford water systems capable of fighting that. I've done systems across California, on Maui, and Santa Rose after the Coffee Fire that melted underground distribution piping.
It is amazing the expertise that resides on the Cardboard! Thanks for posting this.
I would imagine that the pumping capacity to refill the tanks is at best sized to keep up with the "normal" drain over a 24 hour period plus a safety factor. After all, the water usage isn't constant every hour of the day. The inflow only needs to be adequate to refill the tank at a rate such that it never drops below some desired minimum in "normal" use. If there is a wildfire and the firemen are opening all the hydrants I would guess the pumps could not come close to keeping up with the outflow, even if they were all working 100% full blast. Is that correct? I would also guess that the input water supply is not unlimited either, and if all the surrounding zones are suddenly pumping at full capacity that supply could also become a limiting factor. Is that correct? Thanks again for sharing what you do for your "day job" :-).
This is correct. In a "normal" system, demand is highest in summer and usually twice a day (before work and after work) in a diurnal pattern. Water drains from storage tanks during those periods and fills more slowly during off peak hours based on pumping capacity, or sometimes we'll fill lower zones from higher zones, but that means we need to replenish the tanks in the higher zones from some source.
Most often available fire flows are constrained by the pipe distribution network, particularly the size of pipes and how well they are networked or looped on public and sometimes private streets. Looking at a map of Pacific Palisades, there are a lot of long and dead end streets. It isn't a city block system, which is easier to loop the water lines. Having adequate fire flow in Pacific Palisades is probably challenging. Opposed to say, North San Jose, where we have 18-inch mains and plenty of 12-inch loops and really high residual system pressures all fed by a large turnout and big booster pumps with very large storage tanks. We had a contract to do the fire flow modeling and testing. We would routinely pull 8,000 gpm from several hydrants at an intersection with almost no drop in pressure. Once the police car flipped after the officer volunteered to "block" the flow coming out of our giant sock (we advised against for the record), we convinced Muni Water that there is no reason to perform fire flow tests in NSJ because the system is so robust. But if every commercial building was on fire at the same time? Yeah, they would run out of water.
I don't want to give the impression there are no problems with municipal water systems. Like I said, I make part of my living fixing them. The system in Maui was so not up to snuff, that case settled out after deposition and part of the settlement was to build a new system. That was a fun job in a great location. Most if not all systems have deficiencies. Probably where most of us live. Some have major deficiencies. When water rates go up, that's part of the reason. I can't speak to various systems in L.A. We worked once on a waterline on the PCH in Hermosa Beach. Maybe 30 years ago.
(01-10-2025, 10:36 PM)Mick Wrote: The Santa Ynez Reservoir in Pacific Palisades was offline because of repairs to its cover...a 117-million gallon reservoir has been empty and offline since February 2024. Would that have alleviated the loss of water to the hydrants?
I would need to see system schematics to understand how it all works, but most likely the answer is "no". Maybe they could have held out a little longer, but the distribution systems are simply not sized to deliver that much flow to such a large area all at once.
This is simplistic, but let's try to assess the scale of it all. The idea behind fire fighting is not to save individual buildings per se, but to prevent loss of life and prevent the fire from spreading to more buildings. Codes have established that for a typical single story residential home that requirement is something like 1,500 gallons per minute for two hours. The water distribution system needs to be able to get 1,500 gpm on top of all the other simultaneous demands (normally domestic use and irrigation) without too much loss in pressure. The higher the pressure the better. With the Santa Inez Reservoir out of service, the pressure zones it was feeding had to be switched to something else (another reservoir or pumps or fed through an even higher pressure zone). I don't know if that new controlling pressure was higher or lower.
So if we are only trying to save houses, the 180,000 gallons needed to put out that one fire must come from storage (Santa Ynez) or pumps. Again, what replaced the normal operating storage of Santa Ynez? Likely moot, because they weren't putting out one fire. Everything was on fire. I read that 5,300 structures were lost in the Palisades Fire. Plus how many were saved? I can't find that number, but 2,900 acres were burned. At a density of 3+ homes per acre, let's say there were a total of 9,000 structures threatened, so something like a 60% casualty rate. The fire didn't burn 2,900 acres at once, but it moved fast. To protect say 1,000 homes over two hours requires 1.5 million gallons per minute distributed in the system (pretty unlikely to do that) and 90 million gallons out of storage. That's most of the reservoir's stored water assuming it was full when the fire started and without complicating things, a 1,500 gpm or 4,000 gpm fire flow is a criterion used to evaluate and design systems. What flows out of an open hydrant is a function of the system itself, available water pressure during the event, how many pump trucks are hooked up, how many hoses are going, and other things. As I mentioned elsewhere with our San Jose fire tests, they could be pulling even 20,000 gpm over a few city blocks. A massive fire like that is going to drain all the storage no matter what. As Goose said, there is just no way to fill it up quickly enough, and the systems are not designed to deliver that kind of flow rate for so long. It doesn't matter what is happening at the Hollywood Reservoir or in the Owens River Valley, or Colorado River. This is a water storage and delivery limitation, not a water supply limitation.
A full Sanchez Reservoir probably buys them less than two hours before it is empty (or at least so low that there is no longer operating pressure) and the fire rages on. With winds the way they were, who is to say that even those first thousand homes "saved" while they had water in storage (never mind whether it could actually be delivered without collapsing pipes) would remain saved. I'm sure that people will be simulating that after the fact and taking it to court.
One addendum. Reservoirs do need periodic maintenance and refurbishment and are taken offline. You don't do that at the height of summer demand or the summer/fall fire season. You do it in the normally wettest months with lowest demand. The winter. Like now. Expecting them to have known this was going to happen is grossly unfair. Act of Nature.
