Hood Mountain Regional Park at high risk of flash floods and debris flow

While most of Sonoma County’s regional parks are in full or partial recovery from the October fires, two of them – Hood Mountain in the Sonoma Valley, and Tom Schopflin Fields in Larkfield – remain entirely closed, with no set date to open.

For Hood Mountain, the 1,750-acre wilderness park on the edge of the Sonoma Valley, a new danger was revealed with the recent release of the county’s Post-Fire Hazard Assessment report, foretelling high risk of landslides and flooding that might affect the park when, and if, the rains come.

“Cal Fire has told us that a 10-year flood event would be magnified to a 100-year event, because of the lack of the ability of the land to absorb rainfall,” said Melanie Parker, deputy director of Sonoma County Regional Parks. Not only trees and topsoil, but a significant portion of subsoil has been damaged by high-intensity fires.

“One way of looking at burn severity is looking at the soil,” said Parker. “If the fire stays in place a long time or is particularly hot, it will burn down past the duff into the subsoil.” That can cause damage to the micro-root structure in the soil, which in turn can lead to instability and a greater risk of landslides.

Hood Mountain deserves particular attention because if the severity of its burn, which comprised about 60 percent of the park’s area.

“I am very worried about Mt. Hood,” said 1st District Supervisor Susan Gorin at a Board of Supervisors meeting last month, where county officials authorized a year-long contract to evaluate fire damage and create a flood warning network.

On Dec. 26, the county and the City of Santa Rosa released an interactive online map – SonomaCountyRecovers.org/rain-ready – showing which parts of the fire areas in Sonoma, and neighboring counties, are at low, medium or high risk for flash floods and slides of mud and debris.

The map shows that much of Sonoma Valley is at moderate risk in the burn area, but there’s a concentrated area of high risk on the south side of Hood Mountain, along Hood Creek near the Pythian Road park access.

So far, the light rains and sunny weather have been beneficial rather than malevolent. “We’re lucking out,” Parker said, recalling last year’s autumn arrival of the “atmospheric rivers” that dumped over 15 inches of rain in the area during the last three months of 2016. So far, that total is under 5 inches.

Hood Mountain adjoins Sugarloaf Ridge State Park, and it’s the border area of the two parks that was most severely burned in what came to be known as the Nuns Fire – mostly during the second week of the fire, after the area escaped significant damage between Oct. 8 and 12.

“It could very well be closed for a long time, if we do get a major rain event,” cautioned Parker.

But she was hopeful that parts of the park – including the so-called McCormick Addition that links Hood Mountain with Sugarloaf – might be opened up on its own before the rest of the park.

Calling it “a hidden wilderness gem right outside of Santa Rosa,” Parker said the area on the northwest side of Hood Mountain was largely unburned, and the access up Los Alamos Road might be the first to open. The headwaters of Santa Rosa Creek, the Homestead Meadow, and the Grandmother Tree off Headwaters Trail in Sugarloaf are all in this area.

“That’s another one of our favorite hiking locations,” said Bill Myers, of the Bill & Dave Hikes club. He noted that the fundraising Funky Fridays venue at Hood Mansion on Pythian Road is OK. “But we’re not going to be hiking any time soon at Hood Mountain. That’s another problem.”

Other parks that were significantly scorched by the fires, including Sonoma Valley Regional Park near Glen Ellen and Shiloh Ranch near Windsor, are fully open (barring temporary closures due to weather or high winds), allowing day-hikers a chance to see the forest’s natural regeneration in real-time. Those parks don’t have the issues of steep terrain, high-intensity burning and damage to infrastructure (bridges, culverts, trail re-enforcement) that afflict Hood Mountain.

“We’re eager to get people in the parks to see the land’s rejuvenation,” said Parker, who doubles as the county’s natural resource manager. “Most of our plants are adapted to fire, and their regrowth is a powerful, hopeful sign to see the recovery that nature is doing.”

Allowing natural regeneration is much preferred over “re-seeding” the park with fast-growing grasses that might give the appearance of recovery or seem to prevent soil erosion.

“We have to be careful we are not accidentally replacing plants already on site,” wrote Parker recently on the county parks website. “Even ‘native’ seed is not necessarily representative of the plant community that existed pre-fire and (which) will respond on its own post-fire.”

Needless to add, the cost to the bottom line of the Regional Park budget has been “extraordinary,” according to Park. “Park staff was working overtime – our rangers and peace officers are (our) first responders. And there was tremendous damage to infrastructure in many areas, leading to expenses that the county has little idea at present how we’re going to recover.”

It could present a cash-flow problem over time as serious as the flash floods and mudflows that threaten Hood Mountain, as soon as – or if – heavy winter rains finally arrive.

Contact Christian at christian.kallen@sonomanews.com.