By Jason KUROSU
The recent rains of this winter have reignited concerns among those who live in the hillside communities of La Crescenta, Glendale and La Cañada-Flintridge. The Station Fire left the mountains especially susceptible to mudslides and the floods of early 2010 only heightened the collective awareness of hillside residents.
The debris basins atop the hills have withstood the December rains with relative ease, filling up to only 10- to-20% capacity according to city and county officials. Basins such as the Mullally debris basin on Manistee Drive in La Cañada fill with rainwater, mud, sediment and other debris, which is then transported to the Dunsmuir Sediment Placement Site (SPS).
It is at the SPS where new concerns have arisen.
Some of these worries hearken back to a flood in Montrose on New Year’s Day in 1934, which killed over 40 people and destroyed hundreds of homes.
“At the time, 40 people died and hardly anyone was living here,” said Mike Lawler, head of the Historical Society of Crescenta Valley. “Imagine what would happen today.”
The 1934 disaster brought down somewhere around 500,000 to 700,000 cubic yards of debris.
“The debris basins today could not handle that flood,” Lawler said.
Geologist Thomas L. Davis stated as much in a letter to the Department of Water Resources. In it, he states that, “The largest debris basins in the Crescenta Valley portion of the system have a maximum storage capacity slightly in excess of 100,000 cu-yds, yet in 1934 two canyons, Pickens and Hall-Beckley, were the source of at least 500,000-700,000 cu-yds of debris.”
Even with the rarity of a flood of that enormity, the capacity of the SPS is a factor of concern.
Glendale Director of Public Works Steven Zurn said, “This last year saw quite an increase in the amount of soil taken to the site.”
Despite that, Zurn is confident in the structural abilities of the SPS.
“This is an engineered fill site and the County crews have worked all summer and fall to ensure that the placement is stable and sound … The County has maintained the site diligently throughout the rain incidents and it has held up very well. We also have maintained safety measures in the area in the event that we get mud flow from that or any surrounding area.”
There are other concerns, removed from those of the structural capacity of the basin. Residents worry that the hills, from repeated exposure to rain, could be close to reaching the saturation point, when the soil on the hill has absorbed all the water it can, leaving any excess water to proceed downhill.
The location of the SPS itself has also always been a worry for residents and not just because it sits just above their homes. The SPS is built upon a set of fault scarps, or slopes that lie along the Sierra Madre fault system that, according to Davis, “is considered to be seismically active by both the USGS and the California Geological Survey.”
The recent floods of early 2010 have provided residents with much to worry about, but thus far, the SPS appears to be operating smoothly. The unpredictable nature of the weather and geology, however, do much to keep nerves on edge.
“They say it’s really engineered well so that nothing will go wrong,” said Lawler. “[But] I’ve heard of so many engineering disasters where the officials said that before.”