DEL MAR — Tree branches and soil layered to create what is called a willow mattress is the latest plan to help restore an approximately 75-foot section of the Coast-to-Crest Trail, adjacent to Del Mar Horsepark, that was washed away last year.
The proposal was submitted to the California Coastal Commission by the 22nd District Agricultural Association, which owns Horsepark, as an amendment to its development permit.
“There would be thick layers of willow cuttings and dirt,” said Kevin McKernan, executive director for the San Dieguito River Park Joint Powers Authority, which maintains the trail. “The willow sprouts roots and regrows, creating a thick vegetative area.
“The branches slow down the water as it gets higher and it rebuilds itself if it all works correctly,” added McKernan, who said his group proposed using a willow mattress to stabilize the area. “I don’t know that I would call that a solution, though.”
According to a study completed in July 2016 by Environmental Science Associates to assess the site conditions and develop potential concepts for bank stabilization, the area and surrounding sections of bank “are inherently susceptible to ongoing bank erosion.”
There is, however, “potential to locally increase bank stability and the longevity of the current trail alignment by creating a lower gradient bank with more vegetation and a more resistant toe.”
While that will buy some extra time for the trail, it will not reduce the factors causing erosion in that part of the river. In other words, it “will reduce the symptoms and rate of bank erosion but not the causes,” the study states.
On Jan. 7, 2016, following a heavy storm, the bank collapsed and severed the Coast-to-Crest Trail west of the El Camino Real Bridge.
The JPA sought to repair the damage, but a Coastal Commission permit issued to the 22nd DAA includes special conditions that do not allow “channelization,” such as berms, walls, riprap and shotcrete, or “substantial alteration of a river or stream” to protect the development from flooding or the riverbank from eroding.
McKernan said the first proposed solution was to install a railroad flatcar but that was deemed too big for the site.
This past October, McKernan suggested installing a prefabricated, 6-foot-wide, 100-foot-long pedestrian bridge.
David Watson, a 22nd DAA board member, said he opposed the railroad car because he doubted the Coastal Commission would “look favorably on putting an old railroad car in a sensitive habitat area.”
“It would be too much like an armored barrier wall,” he said.
Contrary to what some believe, Watson said, “I am not opposed to a bridge. … An environmentally sensitive design for a bridge is more likely to be approved.”
McKernan said the JPA’s primary interest is keeping the Coast-to-Crest Trail connected and the bridge, estimated to cost $90,050, “seemed like a viable option.”
Dustin Fuller, senior environmental planner for the 22nd DAA, said with the permit application for the willow mattress submitted to the Coastal Commission he will “work with (its) staff to find a compromise solution.”
“Once you put in supports for the bridge, it’s possible it will erode away around it,” Fuller said.
When finished, the 71-mile Coast-to-Crest Trail will connect from the beach in Del Mar to Volcan Mountain near Julian. Approximately 45 miles are complete.