Now that the steep canyon hillsides above the creek are void of vegetation, what happens if landslides or heavy rain wash large amounts of sediment into the water? Local nonprofit The Bay Foundation has begun considering the effects, and how the fire could affect the landscape and the sediment flow to the ocean.
The Malibu Times consulted scientist Tom Ford, executive director of The Bay Foundation, about the possible effects on the Malibu Creek and Lagoon from the Woolsey Fire.
Ford said in a phone interview that the sediment’s effect on the lagoon depends on how much and how hard it rains.
“If it’s a big rain, and a lot of sediment comes down,” Ford said, “we’d expect it to look like it did two years ago after the torrential rains of January 2016.”
In one of the biggest 2016 rainstorms, Ford said the sheer volume of water coming down the creek carried nearly all the sediment and debris straight out to the ocean—it did not pile up in the lagoon. “I saw how blown-out the beach was, and all the driftwood laying on it, and was able to tell that much of the debris made its way out of the lagoon.”
Describing the reconfiguration of the Malibu Lagoon five years ago, Ford said new design elements “should help to keep the sediment from piling up, because the design was based on general knowledge of the lagoon and the hydrology of the water.”
“Sediment is not a new thing,” he explained. “The lagoon was designed to take into account the combination of depth, profile, and the width of the channels to allow for a tidal prism—a natural movement of water into and out of the channels, with a natural flushing into the ocean.”
What happens to the sediment when there’s a landslide in the canyon or it doesn’t rain hard enough to wash out to sea? Ford said, “The sediment just tends to pile up along the sides of the creek and not wash into the waterways.”
In a worst-case scenario, where the amount of sediment that comes down is so great that it actually overwhelms the existing waterways and lagoon system, Ford said that “natural processes and normal patterns, once re-established” would take care of the sediment over time.
In terms of the lack of vegetation along the sides of the canyon, Ford says it grows back via the natural biological process of “succession.”
“In areas that had healthy natural vegetation before the fire, wildlife and other forces will disperse the seeds; and a new generation of plant growth will begin,” Ford explained. “You’ll have the same vegetation that was there beforehand. However, due to the drought, some chaparral was already dead. Those areas could be taken over by non-native grasses.”
“We’ll keep our fingers crossed for the best scenario after the fire, which is that we get small frequent rains, the native seedbank responds and the native vegetation re-grows,” Ford said.
He reported that a Bay Foundation staff member inspecting the Malibu Lagoon on Monday observed “a whole heck of a lot more rabbits than normal”—indicating the small mammals must have found a safe refuge from the fire by escaping to the lagoon area.
Ford had no comment on the fact that the lagoon was breached on Thanksgiving night by concerned Malibu locals just ahead of the rain, who said they were trying to make sure the breach occurred as far away as possible from the historic Adamson House.
Tom Ford is executive director of The Bay Foundation, director of the Santa Monica Bay National Estuary Program and co-director of the Coastal Research Institute at Loyola Marymount University where he is part-time faculty at the Seaver College of Science & Engineering. He’s been studying the restoration of kelp forests since moving to LA in 1998, and is involved in a number of current projects, including the aerial mapping of boats, abalone and sea urchin studies, coastal climate change, and monitoring of Marine Protected Areas.