Two debris basins built in the foothills above Centerville after the 1983-84 floods are inadequate. Larger ones need to be built, at a cost that could top $2 million.
The options to replace the debris basins at Barnard and Deuel creeks were presented at a public hearing last week.Several of the more than 30 residents who attended the hearing oppose the new basins, questioning the engineering studies that determined how much debris may flow out of the canyons and saying the basins may not be able to stop the flow of mud and rock.
According to the city's feasibility study, the Deuel Creek basin will contain 4,500 cubic yards of flow, but the canyon has the potential to slough off up to 250,000 cubic yards.
Depending on the type of construction that could be used, either compacted earth or concrete, a 250,000-yard capacity basin will cost between $1.37 million and $1.71 million to build.
It would be between 90 feet and 100 feet high, 333 feet to 370 feet wide, and have a base between 85 feet and 480 feet wide, according to the studies.
The current Barnard Creek basin is designed to hold 6,000 cubic yards of flow but would be rebuilt to contain up to 18,000 cubic yards, according to the engineering study, which was funded by a $300,000 federal CDBG grant the city obtained last year.
The new basin would cost between $390,000 and $557,000, also depending on its construction material, and would be between 45 feet and 60 feet tall, 120 feet to 170 feet wide, and have a base of between 50 feet and 300 feet.
Davis County Public Works Director Sid Smith said the two current basins were built after the 1983-84 floods as part of a $25 million county flood control effort.
Their capacity was based on a best guess at the time of how much flow the canyons would produce, combined with budgetary restraints, according to Smith and Centerville City Engineer Fred Campbell.
Those flow estimates have since been revised, based on a new method of study developed by the county flood-control engineers. The study looks at the amount of rock and other debris being held in the narrow, steep canyons and how recently the canyons were scoured out by flooding, Smith said.
Residents living below the two canyons in federally designated flood-plain or debris-flow areas have a direct financial stake in the study, Campbell said.
They are required to buy federal flood insurance if their home mortgages are financed through federally insured financial institutions, a stipulation that can cost them between $200 and $300 a year.
If new, bigger basins are built that will contain projected flows, the flood insurance requirement can be waived, according to city officials.
City manager David Hales said there is no funding at present to build the basins.
The city doesn't have $2 million, the county has exhausted its flood-control funds and is still paying off the $13 million in bonds that it sold to finance flood-control works in 1983, and state and federal emergency money has also been used up, Hales said.
Impact fees collected on new homes and earmarked for flood control are generally spent on downstream projects, Hales said, pointing out that new and bigger culverts will eventually have to be pushed under I-15 to handle the city's growing storm runoff volume.
Any funding for the debris basins will have to come from a combination of sources, Hales said, with contributions from the city, the county, and perhaps other grant money.
Archer Clayton, born in Centerville 80 years ago, witnessed the disastrous floods of 1923 and 1930 and said he doesn't believe the debris basins are adequate.
A crest of water 30 to 40 feet high and boulders weighing thousands of pounds poured out of the canyons in those years, Clayton said. The force of the flood, he told the council, would easily have destroyed any dam in their path, adding the debris from the dam wall to the flow.
"Those basins pose a tremendous danger to the community," Clayton charged, adding they would also be any eyesore.
"I love those canyons. I've hiked every one of them since I was a boy and still do three times a week. What an eyesore those basins would be," he said.
Other residents living at the mouth of the canyons said the county has broken its promises of landscaping and maintenance on the basins, made a decade ago when they were built, and they see no reason to believe new promises.