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5 Drainage Culverts Retrofitted For Safer Wildlife Crossing Along 12-Mile Stretch Of State Route 118 In Ventura County

THOUSAND OAKS (CBSLA) — More raccoons, possums, even a bear, are safely crossing a two-lane stretch of State Route 118 in Ventura County, thanks to a joint project between Caltrans and the National Park Service.

118 culvert wildlife crossings
(credit: National Park Service)

Five drainage culverts have been retrofitted for wildlife and fences have been added to the areas to help wildlife cross State Route 118, according to the National Park Service. Biologists say a two-lane highway like State Route 118 appears easier to cross than a busier highway than the 101 Freeway, but are actually a bigger threat to wildlife.

"Most animals won't even try to cross the 101," Caltrans senior biologist Paul Caron said in a statement. "All of these roads – the 125, 118, and others are all interconnected. What good is it if we just focus on the 101, when they all get killed on or are not willing to cross the 118?"

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The two agencies studied the movement, mortality and crossing of animals in the area in order to choose the right culverts that could serve as wildlife crossings. The National Park Service says the study determined that wildlife usually cross roadways where they intersect with riparian areas. Other culverts were deemed inappropriate because of structures blocking the culvert or access to it.

At Long Canyon underpass, a long concrete ramp was built to allow animals to walk down into the culvert to mitigate the 10-foot cement wall blocking wildlife on its north end. Fencing was also installed on the north side of the road to funnel animals onto the ramp. At another culvert dubbed Fox Barranca, Caltrans workers filled a 6-foot drop with a pool of water at the bottom with boulders of varying sizes. The work created a natural-looking ramp into the culvert, especially after soil filled in spaces around the rocks, allowing plants to grow.

The retrofit work is mostly complete and cameras have been set up to monitor the crossings. As many as 10,000 images are being captured monthly by remote cameras, National Park Service officials said. Evaluation of the retrofitting project is still ongoing, but officials say there is already evidence that the wildlife crossing are a success, with some culverts that had almost no use prior to the retrofitting of ramps now seeing daily wildlife use.

bear crossing 118 culvert
(credit: National Park Service)

One of those crossings was a black bear in a box culvert known as LaCumbre, where a steel ramp was installed. The drainage to the culvert passes through citrus and avocado orchards in Somis, and the bear appeared to have come and returned to the Santa Susana Mountains.

"During the year and a half of monitoring along Highway 118 across the two monitoring efforts, this is the only time we have seen a bear in the area," Justin Brown, a wildlife biologist with the Santa Monica Mountains National Recreation Area, said in a statement. "It was kind of a fluke but rewarding to see it use the ramp rather than risk getting hit on the roadway."

Another concrete result of the project is that Caltrans maintenance crews are reporting picking up less roadkill along the 12-mile stretch of Highway 118 that includes the five crossings.

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