DENVER — The Colorado Department of Transportation and Central 70 Project partners say they will investigate what caused Sunday’s flooding on the low-lying portion of I-70 near York Street, adding that the drainage network has yet to be fully completed.
Denver Fire received 78 calls for service between 6:30 and 8:30 p.m. Sunday, including nine from people stranded in water. Eleven people were rescued from vehicles stuck on I-70 at York Street, on the western part of the Central 70 Project, another eight people were rescued from a van at an underpass at 38th and Blake, and others were rescued from the areas of E. 46th Avenue and Washington Street and East 23rd Avenue and Colorado Boulevard.
CDOT spokesperson Stacia Sellers said in a statement Sunday night and in an interview with Denver7 Monday morning that the section of 46th South Avenue that is under construction above I-70 between Brighton Boulevard and York Street – which is directly above where the flooding occurred – is not yet paved and created “exceptionally muddy conditions that may have contributed to flooding.”
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Sellers said that area would be one of the focuses of the investigation into why the flooding occurred.
“The Central 70 Project is going to conduct a thorough investigation to determine what exactly caused the flooding this evening,” Sellers said in a statement. “Fortunately, as an active construction project, if there are any system failures we are able to go in and remediate any issues that occurred during this event. However, without conducting the investigation, we do not know if there was a system failure.”
CDOT explains next steps after Central 70 flooding
Kiewit, the lead company on the project, typically will help pump water out of a flooded area, Sellers said. She said once the drainage system is completed, the area of I-70 that flooded “is expected to withstand a 100-year storm event.”
Typically, the pumps that are used will suck the water out of an area to a pump station, where it is processed and released if it is clean, Sellers said in an interview. Kiewit will be leading the cleanup effort in the wake of the flooding.
Video: Denver firefighter rescues 2 children from flooding
“We’re going to see exactly what happened and try to remediate that as quickly as possible, so in the event of a future rainstorm – especially the heavy rainfall that we saw yesterday – this doesn’t happen again,” Sellers said.
There are few stations that measure precipitation in the exact area where the heaviest flooding occurred, but approximately 2 miles to the south, the Denver Zoo received 1.85 inches of rain, according to the Mile High Flood District. Near 64th Ave. and Pecos Street about 3 ½ miles to the northwest, about 1 ½ inches of rain fell.
Most of the rain in the storms fell in about 30 minutes. The Denver 3.2 SSE station recorded 0.71 inches of rain in 20 minutes on Sunday.
A 2015 report published in Flood Hazard News explained that at least one rainfall event every year in the Denver-Boulder area exceeds the “100-year storm” threshold. The ALERT Flood Detection system predicted a maximum of 2.6 inches of precipitation in one hour for Sunday’s “high threat” forecast.
The latest NOAA Atlas 14-point precipitation frequency estimates for the area that flooded on Sunday shows a “100-year” precipitation event in the area would mean 2.38 inches fell in one hour; 1.93 inches fell in half an hour; 1.4 inches fell in 15 minutes or 1.14 inches fell in 10 minutes.
Officially at Denver International Airport, only a trace of rain fell. The daily record for Aug. 7 was 0.95 inches in 1973. Typically, by this point in August, Denver has received 0.48 inches of precipitation.
Over the past four years, the City of Denver has completed several stormwater projects, including one that traps stormwater runoff from the area at the northeast corner of the Park Hill Golf Course and a floodwater channel along 39th Avenue between Franklin and Steele streets which the Central 70 Project took into account during planning and construction.
Sellers said that Kiewit and subcontractors would conduct a thorough investigation of the flooding while the construction is ongoing.
“Our systems aren’t 100% complete. Just as any construction project that’s in an interim phase, you run a risk of potential flooding in a construction zone, but we’re still going to conduct a very thorough investigation to see exactly what happened,” she said.
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