Ulysses90 said:
ABATTBQ11 said:
Reservoirs were never a problem. LA had billions of gallons of water. The problem was always pumping capacity and getting that water to a higher elevation.
The city's water mains are designed for supplying drinking water and fighting individual house fires, not a forest or massive brush fire spreading to homes and neighborhoods. When every hydrant for miles is being tapped and water is leaking from burned out structures, there's so many outlets and so much demand on the system that there's no way to keep up pressure and flow. All the water in the world does no good if you can't maintain line pressure to get it where you need it.
When you think about the main trunk lines in comparison to the size of the fire, it's like trying to fight a house fire with your garden hose and shower heads. It's just not going to work.
I don't believe your initial statement about the reservoir is correct. There is a 117 million gallon reservoir uphill from Pacific Palisades in Santa Ynez Canyon. It was specifically for fighting fires like the one that devastated Bel Air and Brentwood in 1961. It is at slightly higher elevation that the neighborhoods that were below it so gravity would feed the water to the hydrants and the pumps on firetrucks could help increase pressure at the nozzle.
The Santa Ynez reservoir was empty when the fires hit Palisades in January. This article deacribes why it was empty for repairs to the protective cover over the water.
https://www.latimes.com/california/story/2025-01-22/why-has-a-reservoir-in-palisades-stood-empty-for-a-year
https://www.cbsnews.com/news/la-fires-santa-ynez-reservoir-pacific-palisades-california/Quote:
David Freyberg, PhD, a hydrologist and water resources specialist at Stanford University, told CBS News in an email that while a full Santa Ynez would have had benefits, it's not clear how much impact it would have had.
"The reservoirs above Pacific Palisades were not designed to support fire-fighting at the scale of [this] fire," he wrote. "Water supply reservoirs are typically designed to cope with house fires, not wildfires."
He added that the situation has made it clear that larger-scale solutions are necessary.
"It is clear that communities vulnerable to wildfire are going to need to think carefully, i.e., rethink, about design criteria for these systems," Freyberg said. "Not just reservoirs, but pipe sizes [and] pressure management."
Being slightly higher only slightly helps because pressure is driven by the height of the water column. The volume is irrelevant. The real drivers of water pressure were the 3 one million gallon tanks that sat at much higher elevations and were being constantly refilled by a series of pumps. As long as the demand for water exceeded the pumping capacity, a loss in pressure was inevitable as the flow delta between demand and supply drained the buffer in the tanks.
While fire trucks can pump water at the hydrant, this is not really a solution to the problem because the issue is the pressure in the trunk lines and mains that pushes flow to the hydrants the trucks pump from. While gravity would pull water down to the hydrants, hydraulic loss would limit the available flow rate. That's why water pressure is really high next to water towers and much lower farther away. Added pressure downstream from the hydrant to the nozzle doesn't do much to increase the flow rate from the reservoir to the hydrant. In other words, you can pump from the truck all you want, but if there's not enough water getting to the hydrant, there's nothing to pump out of it.
Now, you might think that those pumps should be able to just suck water from the system, but, again, you have to account for hydraulic loss and the bottleneck of the system between the truck and the reservoir. It's like trying to chug a beer through a 100' straw.
