Can Debris Basins Handle El Niño?

File photo The capacity of local debris basins is being called into question as residents wonder if they can handle the deluge expected from the upcoming El Niño storms.
File photo
The capacity of local debris basins is being called into question as residents wonder if they can handle the deluge expected from the upcoming El Niño storms.


With the massive El Niño season on its way, residents throughout the Crescenta Valley are preparing for a very wet winter. Sandbags are available at several park locations throughout Crescenta Valley and Glendale areas, emergency kits are being made and one topic on many residents’ minds is that of the local debris basins. After the 2009 Station Fire, the following winter rains and subsequent flooding hit the foothills area hard and filled many of the debris basins along the foothills with sediment washed down from the mountains where there was no vegetation left to hold it in place. Now, six years later, the debris basins are still a hot topic.

One of the most talked about basins is the Dunsmuir Debris Basin in Dunsmore Canyon. A 2010 letter from Consulting Geologist Thomas Davis to the Division of Safety of Dams suggested that the Dunsmuir Debris Basin be transferred to the state’s jurisdiction.


“Dunsmuir Debris Basin, which is located in Dunsmore Canyon, is of limited height and storage. Based on the chart of Division of Safety of Dams (DSOD), it does not meet the criteria to be under the jurisdiction of the State,” said Kerjon Lee, Public Affairs manager, L.A. County Public Works, in an email interview with CV Weekly. “It is not currently under the state’s jurisdiction. L.A. County Public Works has contacted DSOD and is awaiting a response.”

The basin is used to capture any of the mud, dirt and rocks that wash out of the mountain during intense downpours. This basin, along with several others located along the foothills, keep debris from washing into local streets and homes. After the winter 2010 floods, many of the debris basins were near or at capacity. Since then, work has been done to clear them out in anticipation of future needs.

“Under L.A. County’s maintenance criteria and environmental permits, a debris basin will be cleaned out when it is 25% full, under unburned watershed conditions, and when it is 5% full under burned watershed conditions,” Lee said. “Dunsmuir Debris Basin was cleaned out in fall 2009 after the Station Fire and after the January/February 2010 storms. Since then, no cleanout has been necessary since debris accumulation in the basin has been limited under ongoing drought conditions. Currently, the debris level in Dunsmuir Debris Basin is below 5%.”

While the expectation for the coming El Niño season is for massive amounts of rainfall and flooding, it won’t be as drastic as the 2010 storms that filled the debris basins. The area is no longer under freshly burned condition and therefore will stand a better chance against the coming rains, as the vegetation which has regrown the last six years will provide solidity to the loose debris and soil.

That being said, water is still a danger for local homes. Even though debris may not be washing out of the mountain at the same rate it was after the Station Fire, the amount of rain expected will exceed anything we have seen in the last 15 years and therefore could cause flooding not of debris but of rain water. L.A. County Public Works will continue to monitor the debris basins throughout the season and will take action as necessary.

“Under any future storm event, if the debris basin is 25% full or more, it will be cleaned out,” Lee said.

To find out how homeowners can prepare themselves and their homes for El Niño season, visit