Flood's toll

The following data represents 313 destroyed properties in Boulder County. Some properties saw multiple structures destroyed, bringing the destroyed structure total to 337.

Boulder:

49 properties destroyed in 100-year flood zone

12 properties destroyed outside 100-year flood zone

Longmont:

54 properties destroyed in 100-year flood zone

3 properties destroyed outside 100-year flood zone

Jamestown:

20 properties destroyed in 100-year flood zone

6 properties destroyed outside 100-year flood zone

Lyons:

82 properties destroyed in 100-year flood zone

0 properties destroyed outside 100-year flood zone

Superior:

1 property destroyed in 100-year flood zone

0 properties destroyed outside 100-year flood zone

Unincorporated Boulder County:

54 properties destroyed in 100-year flood zone

32 properties destroyed outside 100-year flood zone

Source: Boulder County Assessor's Office

September's historic flood destroyed a total of 337 structures on 313 properties in Boulder County, representing $41 million in market value, according to newly released data from the Assessor's Office.

The county is waiving taxes on those ruined properties for Sept. 13 through the end of the year, meaning taxes won't be levied against a combined total of $12,367,815 in market value. That figure counts only the value of the destroyed structures, and not the value of the land on which they stood.

Of the 313 properties destroyed in the county, 260 lay within the 100-year flood zone, while 53 did not.

Every one of the 82 properties in Lyons that were destroyed lay within the 100-year flood zone. In unincorporated Boulder County, however, while 54 of the destroyed properties sat in the 100-year flood zone, 32 did not.

Boulder County Transportation Director George Gerstle said the county is already in the process of considering a remapping of the floodplain, based on data from the September storm.

"We will be taking a systematic look at where the floodplain should be re-evaluated over the next few months or six months," Gerstle said. "We're starting a planning process to identify what happened to the streams since the flood, how they have changed since before the flood and what the implications of those changes are.

"As part of that, we will be identifying where we think they changed enough that it would indicate a remapping of the floodplain to reflect what we've learned."

This comes on the heels of the county having updating the floodplain maps as recently as two years ago. Now, the events of September dictate that they must be reconsidered. It is not a simple process.

"Our goal is to have identified those creeks that should be remapped by July, and then it probably takes a year to two years to go through the whole process of remapping, and getting FEMA approval for those new maps," Gerstle said.

"Until that happens, we'll be giving people the best information we have of what happened, and helping them understand the risks, as we understand them, of building or rebuilding in those locations."

Boulder has 14 tributaries, plus Boulder Creek, which flow through the city, and remapping efforts were already under way before the flood for some of them, including Two Mile Canyon Creek, Upper Goose Creek, Skunk Creek, King's Gulch, Bluebell Canyon Creek, the Boulder Slough and Boulder Creek itself.

"Basically, because of the large number of creeks we have in town, we are in a continual cycle of mapping and mitigation. We already had various areas where we were in different stages of either studying or going through the map adaptation process, or pursuing mitigation measures," said Jeff Arthur, Boulder's director of public works for utilities.

"That will continue. The question will be whether there are areas we will be able to move up in priority, based on the significant amount of new data that we have" since the flood.

As revealed by the Boulder County Assessor's Office data, the most concentrated destruction in Boulder was on Manhattan Drive, where 28 properties were lost; Birchwood Drive, where 16 were destroyed; and Manhattan Place, with 11 categorized as destroyed. Many of those were apartments or condominiums.

By contrast, while Lee Hill Road -- which runs up into the foothills -- saw some dramatic upheaval to the surrounding landscape, just two homes on that road were deemed destroyed.

Boulder County Assessor Jerry Roberts said destroyed structures -- most of them homes, but including as many as 10 businesses -- will be taxed through Sept. 12. But no taxes will be levied on them for the balance of 2013, starting Sept. 13.

More than 17 inches of rain fell in some areas of Boulder County from Sept. 9 through 16, but the heaviest rains fell Sept. 11 and 12.

"Not really knowing when all the damage occurred, we took it from the 13th, and basically divided by the number of days that still remained on the calendar," Roberts said. "In other words, they're not taxed on the structure for Sept. 13 through Dec. 31, but they were taxable up to Sept. 13."

The destroyed structures will cost the county about $30,000 in combined taxes for the 110 days of 2013 that the affected properties won't be taxed.

Mobile home parks on St. Vrain hit hard

The highest concentration of destroyed properties in the county, according to Roberts, was in two mobile home parks along the St. Vrain River: the 32-space Riverbend Mobile Home park in Lyons and the 60-space Royal Mobile Home Park in Longmont.

To qualify as destroyed by the county's estimation, Roberts said, structures had to be knocked off their foundation, missing walls or a roof, suffered flooding up to the ground-floor door knobs, or, Roberts said, left "leaning at an angle that was unintended."

Not counted as destroyed in the assessor's tally are homes or structures that are fine even if the bridges leading to them were swept away by the torrent.

"There's nothing in the statute that says anything in terms of prorating for (loss of) access in 2013," Roberts said, "so we wouldn't have done anything with it for 2013. But in 2014, we'll look at it and say, 'Is the access still missing, and how does that affect the market value of the property?'"

Not all of the properties classified as destroyed by the Assessor's Office will necessarily stay that way.

"For example," Roberts said, "there is a condo complex on Manhattan Drive (in Boulder) where the water came straight down and hit the garden-level condos, and on that whole first level they were flooded well above the first-floor living space doorknobs.

"As of January 1st, they will probably have them cleaned out, the drywall replaced, and we'll probably put them right back on (the tax rolls) with no further proration."

Assessor's count could still change

Roberts also allowed for the possibility that not every single destroyed property has been counted, even two and a half months after the storm.

"The number could be subject to change if someone says, after the first of the year, 'Hey, you missed this; how come you didn't prorate me?' It could be back up in areas we couldn't get to because there weren't any roads," Roberts said.

The damage assessments made use of satellite imagery and some aerial photography, Roberts said, but that likely wasn't infallible.

"It's possible that something could have been hidden by the trees," he said.

Gerstle said the existing floodplain maps for unincorporated Boulder County performed well.

"Where people were affected by the floods, and had made changes as a result of the floodplain development program, they were generally happy. They survived because of requirements for developing in the floodplain," Gerstle said.

"On the other side, there were floodwaters that went where we hadn't anticipated. Hopefully, we can learn from that, moving forward. In summary, the floodplain requirements are good. We just need to get better on determining where the floods will be."

Gerstle also said the days of building mobile home parks in the floodplain are likely past.

"I think people have learned what the risks are from flooding and being near streams, and that those risks are particularly high when they are mobile homes because they are not as substantial a building as a normal house," Gerstle said.

Earlier this fall, the city of Boulder released preliminary findings that the flood caused $48.91 million in damage to city infrastructure, parks and open space.

Additionally, Boulder County shortly after the flood put the damage to county roads and bridges at $89 million, and damage to county buildings at $1.3 million.

Contact Camera Staff Writer Charlie Brennan at 303-473-1327, brennanc@dailycamera.com or twitter.com/chasbrennan.