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County explains new flood map to Vallecito residents
7/11/2008 By: Carole McWilliams
Upper Vallecito residents turned out on July 1 to look at new flood plain maps for their neighborhood.
Some were comforted, some weren’t.
The maps showed one of the big problems there – the changeability of the maze of stream channels in a major storm, such as one that hit in October of 2006.
County Emergency Management Director Butch Knowlton told residents that in a 100-year storm, an area with 491 homes would be the funnel point for
It was one hot and fun Fourth of July on Friday
as thousands of people filled downtown
Bayfield for the annual parade and
gathering in the park. The Mill Street
Drug pet parade attracted lots of
participants, while the Lewis Merc
float featured some cool water action.
Koda, above, an Alaska malamute belonging
to Gail Jones of Bayfield, had the proper
attire for the day.
runoff from 96 square miles up the Vallecito Creek valley, which is 20 miles long.
Of the 491 homes, 326 are in the flood plain on the updated map. So are 593 unbuilt lots. The map is based on aerial photos and a topographic map produced after the 2006 flood, Knowlton said.
The 2006 flood had around 4,000 cubic feet per second flowing into the lake from Vallecito, Grimes, and Berri Creeks, he said.
Knowlton reminded people at the meeting that the 2006 storm was not a 100-year flood. In a 100-year flood, that total would be just over 10,000 cfs, with 9,200 cfs in Vallecito Creek and 750 cfs in Grimes Creek.
The flood plain and floodway (the most hazardous part of the flood plain) maps control what homeowners have to pay for flood insurance, and the hoops they have to jump through to get a building permit.
Knowlton, who also is County Building Department director, said it was apparent before 2006 that the old map wasn’t accurate.
“I felt bad because I was bound to make someone go through a flood plain study because their land was shown on the flood plain. It cost people money to prove they weren’t,” he said.
Stream channels change, both because of sediment and debris carried down in high water and because of human activity.
Knowlton said a new sand bar that appeared on Vallecito Creek during the 2006 storm pushed the channel to threaten a house that met the county’s 50-foot stream setback when it was built.
Human activity is a major concern. “We restrict and monitor activities within the channel, and especially the floodway. We don’t want changes affecting someone else. People don’t understand. Man-made alterations affect up-stream and down-stream properties,” Knowlton said.
Every home built in the flood plain must have a foundation that goes at least 12 inches above the 100-year water level, he said. But as more homes are built in the flood plain, their cumulative effect can eventually raise the 100-year water level, he said.
Asked what residents can do to reduce their risk, Knowlton said, “We have several hot spot worry areas. Our ability to help financially, it’s just not there. The only way you can really start addressing these issues is to create a special taxation district to put money into a kitty. … Tax yourselves to raise money for studies, an organization to get grants,” to do the work.
He agreed some people will oppose more taxes for anything. But he warned, “Mother Nature will overtake this valley some day. Mother Nature wants to get away from a channelized stream to a braided system. That’s what she likes. To me that’s the only solution.”
He added, “When that 9,000 cfs comes down, it has to have a place to go. What we really should have done is not let you move here.”
Consultant Greg Koch, who did the flood plain study for the county, said a 100-year flood means there is a 1 percent chance of flooding in any year. “2006 was about a 20-year event,” he said. That’s a 5 percent chance in any year.
Knowlton said he has a lot of confidence in the new map. The county has to map and regulate activity in the 100-year flood plain, but he said he’d like similar data for 10- and 20-year floods, to know which residents need to be notified when a strong storm is coming.
“We’ll have a better idea who will be affected and what roads we can drive on,” he said.
The new maps were produced with funding from the Colorado Water Conservation Board and Federal Emergency Management Agency. Koch said the new maps will be adopted by FEMA in about four months. Knowlton said it could take longer.
Koch advised, “A lot of time, flood insurance is looked on as a bad thing. But in a place where the flows are so changeable, anyone close to a 100-year zone should consider buying flood insurance if you can afford it. If you are in the 100-year flood plain, your mortgage company will require it. The new map will affect that.”
The insurance premiums are a lot lower in a 500-year zone than a 100-year zone. Koch said people who have insurance for the 500- year zone will be grandfathered at the lower premium if the new map puts them in the 100 year zone.
He suggested residents in that situation might want to act on that before the new map becomes official.
The big storms tend to happen in September and October. Asked if the lake can handle the water in a 100-year flood at that time of year, Knowlton said, “For a few hours… When we get a major in-flow, I have a few hours before I have to think about Bayfield and Ignacio.”
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