HIDDEN VALLEY LAKE >> Several hundred homes in this gated community of about 5,500 residents face flooding this winter even as workers scramble to complete flood control projects ahead of the heavy rainfall expected in coming weeks.
This flood control work is in addition to repairing and replacing water and sewer infrastructure damaged or destroyed in September’s Valley Fire that swept through Cobb Mountain, Middletown and Hidden Valley Lake (HVL).
All of this work comes as the HVL Community Services District (CSD) has “zero budget” for flood control, said interim General Manager Matt Bassett. The projects are expected to cost between $600.000 and $700,000 with most money coming from Valley Fire insurance settlements. The flood control part will cost about $200,000.
One of the major problems is that even when fully operational, the HVL flood control system is designed for 10-year floods and the county is expecting 100-year flooding this winter, primarily from January through March during the anticipated El Niño.
What this means is that if long-range weather forecasts are accurate, in a worst-case scenario, there are parts of the community that will flood despite the district’s current flood control efforts. This is because much of HVL is in an officially-designated floodplain with the flooding threat coming primarily but not exclusively from Putah Creek and the many tributaries that feed it.
Among structures in the flood plain are the HVL Campground, CSD office and the HVL fire station. While flood waters are expected to come primarily from Putah Creek, other creeks in HVL-area are also likely to flood this winter, including Coyote and Gallagher.
Rain runoff from Cobb Mountain and Middletown, areas heavily affected by the fire, naturally will channel down and into Putah Creek, causing it to flood. The creek skirts the southern and southeastern edges of the community.
The runoff is made worse by the burned, barren ground that turns to a concrete-like material that allows water to flow rapidly and not get fully absorbed into the ground.
This dangerous situation is compounded by the lack of grasses, brush and trees that act as natural flood and erosion controls.
Of the community’s 2,500 homes, about 300 are in low-lying areas near Putah Creek that are “most susceptible” to flooding, Bassett said.
“We don’t know if it’s going to be just flooded streets or Valley Fire level flooding,” meaning a catastrophic event, he said. To emphasize how serious the district takes the coming El Niño monsoonal weather event, Bassett added, “This is the first time ever that we have thought about flooding on this level.”
One thing is certain: the district does not have the capacity to handle the expected water levels when it’s flood control basin exceeds capacity, which Bassett said it is expected to do this winter.
With a 100-year flood event, an estimated 550 cubic feet per second (cfs) of water is expected to enter the catch basin yet the basin’s lone pump, which is currently under repair from fire damage, can only pump out 18 cfs.
“We’re about 25 pumps short,” Basset said. Even with two additional pumps recently added to the catch basin, the district will increase its basin pumping capacity to only about 44 cfs, still way too little to be effective against a 100-year flood.
The cost of addition pumps is prohibitive, Bassett said, especially given that the CSD has no money for flood control.
He said that as the district prepares for floods, HVL homeowners should be doing the same. He urged residents in the low-lying areas to have a plan on quickly getting to higher ground.
“People need to assess where they live and what resources they have to protect them and their property,” including tarps, sandbags and emergency supplies such as extra food, water, flashlights and batteries, Basset said. “They need to identify what their exit strategy is and then identify what their backup plan is.”
Also, residents should know that there is a sandbag filling station, with sand and bags, adjacent to the South Lake County Fire District station on Hartmann Road, Bassett added.
The district’s flood control catch basin, located off Hartmann Road near Gold Flat Court, is separated from Putah Creek by a dirt levee and Bassett said he has two concerns with the levee during flooding.
First is that the district will not have the ability to pump water out of the basin fast enough once Putah Creek rises, causing a breech between the basin and creek and subsequent flooding.
Second is the need for some kind of early warning system to notify residents when the levee has been compromised and flooding begins. Right now, the district plans to notify residents of an emergency via social media and direct telephone calls.
“We need to educate locals about this and how they will be warned,” Bassett said. He added that the best early warning might be a system of the old-fashioned air raid type of siren.
As of Thursday, Putah Creek near Guenoc was at 6 feet 8 inches and was expected to crest at 8 feet on Sunday, according to data from the California-Nevada River Forecast Center. A week ago, it was half that level.
The monitor stage of the creek’s water level is 19 feet, flood stage is 21 feet with evacuations starting at 25 feet. The discharge rate of water in the creek was nearly 400 cubic feet per second on Thursday, compared to about 25 cfs on Wednesday, indicating a swift current.
Of the district’s three water wells, two were damaged in the fire and one was destroyed. Currently, one well is operating under emergency conditions. The district has also brought in a large electricity generator on a flatbed truck to power the system while the electrical control panels undergo repair.
Bassett said the water projects are completed and the flood control project is about half finished. “We need full ability before the big rains come,” he said. “That is our biggest concern.”
