The answer remains: No one is totally sure, yet.
From Sept. 9 to Sunday, Sept. 15, National Weather Services rain gauges in Boulder mostly ranged in seven-day totals from 14 to 17 inches. One, in the southeast part of the city, recorded 21.1 inches for the week. In a statistical sense, given data the NWS has to work with since rainfall record-keeping began in Colorado in the 1880s, 14 inches of rain in Boulder in a week would happen on average less than once every 1,000 years. The NWS charts don’t measure probability beyond that.
“We are in uncharted territory,´ said Nezette Rydell, meteorologist in charge at the NWS forecast office in Boulder.
Longmont, which has been hit hard by flooding of the St. Vrain River and Left Hand Creek, has had anywhere from 6 to 8 inches of rain over the past seven days. Eight inches of rain in a week in Longmont is close to once-every-500-years territory, according to the NWS probability charts.
Lyons, cut off by flooding of the St. Vrain, received close to 10 inches.
Information on stream flows and the volume of water coming down various canyons is still being tallied. Some of the figures aren’t crunched until the flooding has stopped. But there’s also the problem of measurement equipment being wiped out by the flooding.
United States Geological Survey spokeswoman Heidi Koontz said at least nine USGS stream-flow gauges in the state have been knocked out. Koontz said it could be a couple of days until the USGS has concrete figures like the number of square miles that have been flooded. There have been some media reports estimating that 4,250 square miles have been flooded.
The Boulder Creek, measured at a USGS gauge near 75th Street east of Boulder, was flowing at 2,220 cubic feet per second as of noon Monday. That’s more than 4,200 percent above average for Sept. 16.
“We have other strategies that we’re using and tools we’re deploying to get those other measurements,” Koontz said.
Xcel Energy Inc. also is having a tough time assessing the overall impact flooding is having on its infrastructure.
Xcel spokeswoman Michelle Aguayo said the company hasn’t been able to get into the areas it needs to in order to assess damage to its infrastructure because of road closures and ongoing flood danger.
As of Sunday night, Aguayo said about 1,400 customers remained without electricity in the Boulder area.
“The numbers are relatively small,” Aguayo said of the outages. “But we know how impactful it is (to customers) because of the natural disaster that is accompanying it.”