September 21, 2008
Floods Are Threat Here. Are You Even Worried?
By Jodi Rogstad
By Jodi Rogstad
CHEYENNE - To Cheyenne's earliest settlers, the tan prairie and ribbon-thin creeks betrayed no hint whatsoever that these lands could flood.
Today, despite proof to the contrary, that belief seems to prevail.
Twice, in 2000 and 2004, Cheyenne voters rejected a storm sewer utility. Also, only 30 percent of Cheyenne residents have flood insurance - and these are the people who live in areas prone to flooding.
Meanwhile, the city and county have removed hundreds of structures from the 100-year flood plain in the past decade, thanks to grants.
See Floods, page A16
Continued from A1
However, these projects are a double-edged sword, said city engineer Ken Lewis. It lends a false sense of security because there are still $100 million worth of projects left to do - among them that storm sewer utility that voters rejected twice.
"The city and the county have been knocking out big improvement projects, but it's not enough," Lewis said. "And it's not going to happen soon enough to protect us from the next flood. You never know when the next event will be. It could be tomorrow or 20 years from now."
Cheyenne's complacency is understandable. The Capital City gets about 13 inches of precipitation a year - nearly 40 inches less than New York City. Life in Cheyenne means we can't water our lawns whenever we feel like it. If you plan a picnic, rain isn't a concern - it's the wind.
As Don Beard told the Wyoming Tribune Eagle in December, "When you look at all these dry basins and everything in Wyoming, it just doesn't set in." Beard is the county's flood plain administrator and director of public works.
What doesn't set in is that when it rains a lot in a short time, with the aid of hills and the force of gravity, bad things happen.
That was the case on Aug. 5, when more than two inches of rain fell in one hour, pounding Cheyenne fast and furious.
Aside from the many stories around town about flooded streets and structures - including the 13.5 feet of water that poured into the basement of the Cheyenne Civic Center - you can see the difference it made in Crow Creek alone by simply looking at the creek discharge data that comes from U.S. Geological Survey monitoring.
On July 31, Crow Creek reached its lowest discharge rate for the year at 0.42 cubic feet per second. Using a calculator on western- water.com, that translates into 188 gallons per minute.
Days later, on the day of the storm, the discharge rate swelled to 30,520 gallons per minute. That is not the peak - the USGS data shows only the mean for the day.
However, it was an even bigger event that got the city and county taking a very hard look at flood control.
It was the flood of Aug. 1, 1985. More than 6 inches of rain and hail fell in three hours; 12 people died.
As a result of planning following that storm, the city narrowed the list with three top-priority flood control projects. The criteria: Would it save lives? Would it save properties? And is there potential for outside funding?
These projects are:
- Widen Crow Creek's man-made channels, or culverts, at Morrie and Warren avenues. This was done with a $1.6 million FEMA grant, with a city match. This brought 113 homes and businesses out of the flood plain and was completed this summer.
- Divert waters that flow down Dry Creek's Sheridan Reach to three massive retention ponds. FEMA awarded a $2.8 million grant for this project. The city is making up the difference of the $3.9 million project with fifth-penny money and reserves. Work is under way.
- Build a detention pond on the northeast corner of the Converse- Pershing intersection that will hold 27 acre-feet of water. By adding inlets to existing sewer lines, this will divert water from low-lying neighborhoods southwest of this corner. The city got a $1.45 million FEMA grant for the project and will call for sealed construction bids in October. This area is considered a special flood hazard, however; to protect this from a 100-year flood event, it requires additional piping.
Laramie County also has been doing flood control in the form of Allison Draw, which is a man-made channel that winds though a highly developed area of Laramie County south of Interstate 80.
Phases one and two have already been built, though the county is looking at grants to fix design flaws.
Recently, the county got a $1.8 million grant from FEMA to build phase three, which will channel water from the Orchard Valley Subdivision.
Dry Creek diversion
A thread of a creek runs between Sheridan Street and Dell Range Boulevard - behind Sonic and the Bicycle Station. This is Dry Creek, though this stretch is referred to as Sheridan Reach.
When you turn off Dell Range, you'll see yellow signs warning of a flash flood hazard.
Sheridan Reach just doesn't have a "whole lot of capacity," said Gene MacDonald, the city's former storm water drainage engineer. So when it rains a lot in a short time, waters overflow the banks and fill the streets, covering Converse Avenue, Windmill Road and Hilltop Avenue.
That is why most of the 1985 flood victims lost their lives here, MacDonald said. In nearly every case, people tried to cross in their vehicles to get home.
"Unfortunately, no matter how much you educate people, you're going run into that thing," MacDonald said.
Water's "ephemeral" in these parts.
"People aren't used to flowing water, and it doesn't take a lot to move a vehicle," MacDonald said.
Turn your gaze to the south, across Dell Range. Behind the Greenway and Cahill Soccer Park, there's a lot of digging going on.
This is the end of a chain of three detention ponds.
Water will travel to the three ponds via giant cement underground pipes that will lie beneath the Greenway, Converse Avenue, Windmill Road and Ridge Road. Instead of spilling the banks of Sheridan Reach, water will be diverted to this west-to-east channel instead.
The ponds will have a capacity of 300-acre feet of water - that's 96 million gallons.
To lend some perspective, the Municipal Pool holds about 200,000 gallons.
The pond behind Cahill Park will be wetlands, said assistant city engineer Jeff Fanning.
The city got a grant from the Environmental Protection Agency to put in plants and grasses that will filter out sediment before the water flows out of a 78-inch cement pipe that will gradually release the water back into Dry Creek.
The wetland pond, or Pond 3, is "teensy" in comparison to the others that are coming. Still, it's pretty imposing. When filled with water, it will be about 20 feet deep - more than your average swimming pool.
"You stand on the edge of it, and it's like, 'Oh my God, that's a hole,'" Fanning said.
The second pond will border the north side of Prairie View Golf Course. Pond 1 will lie south of the Junior League Baseball Complex and Powers Field.
The water will start its journey from the already-existing Carey Reservoir, a big grass-covered pit that lies along the Greenway. Water from Dry Creek is channeled here. It holds up to 107 acre- feet of water, or nearly 35 million gallons of water.
Construction costs are $3.9 million. A grant from FEMA is covering $2.8 million of the costs. The deadline for construction to end is August 2009.
This is a huge project, Fanning said. However, there are limits. This is designed for a 100-year flood, an event that can occur once in every 100 years. It is not designed for a 500-year flood event - a truly large "act of God."
"No municipality can afford to prepare for all storm events," Fanning said.
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