Denver Models Good Stormwater Management

March 30, 2016

Stormwater runoff in Denver, CO, flows to two entities: Cherry Creek and the South Platte River. Maintaining and improving water quality in the city’s two main bodies of water is critical to Denver’s present and future.

Cherry Creek North and Cherry Creek Shopping Center are major parts of a residential and commercial district that begins five minutes from downtown Denver. The district is linked by a 22-mile bike path.

The actual Cherry Creek forms the southern border of the district. It flows northwest through Denver, turning into an urban stream. Cherry Creek joins the South Platte River at Confluence Park in central Denver, just west of downtown. This location is about 5 miles east of the foothills, near the site where the city of Denver was founded in 1858.

The South Platte River begins southwest of Denver in Park County, CO, where the South Fork and Middle Fork meet, approximately 15 miles southeast of Fairplay. From South Park, the river passes through 50 miles of the Platte Canyon.

The North Fork joins the river before it emerges from foothills southwest of Littleton, a suburb of Denver. One of the river’s seven dams, at Littleton, was built in 1965 in response to a major flood. The dam created the Chatfield Reservoir, which is a major source of drinking water for Denver.

Because floodwaters pay no heed to jurisdictional or governmental boundaries, it behooves communities to work together on preventing and managing floods. A regional agency makes such action possible, financially and physically. Denver and the communities that surround it have such an independent regional agency in the Urban Drainage and Flood Control District (UDFCD). Established by the Colorado legislature in 1969, the agency assists local governments on multi-jurisdictional drainage and flood control issues.

Credit: Wenk Associates
The Taxi rain swale at seven years

UDFCD covers an area of 1,608 square miles. That territory includes not only Denver, but also sections of the six counties that surround the city and all or parts of about 40 incorporated cities and towns. More than 3,500 miles of streams flow within the area. The population served by UDFCD is approximately 2.8 million people.

UDFCD has become known not only regionally but also nationally for the innovative stormwater management software it has created. These various software models are on the agency’s website and can be downloaded by anyone at no charge.

“Water quality is certainly very important. It should be taken seriously. That’s why we did this, to be sure facilities were being implemented,” says Paul Hindman, UDFCD’s executive director.

Reflecting on such matters as the need for a watershed approach to managing stormwater and the increasing use of green infrastructure, Hindman emphasizes the need to make wise choices based on carefully analyzed data. Obviously, well-designed software is a significant help in making such choices for managing stormwater effectively.

“Many people venture into this area because they’re being forced to by regulation,” he says, “but I would say that we knew it was an issue and started [working on it], so we had a jump start.”

Hindman says that all of the UDFCD software is “extremely well-received. The local governments really encourage the developers to use it so there’s some consistency in design throughout the metropolitan area.”

The district began creating modeling software in the 1970s. “We looked at hydrology modeling tools that were available nationwide and tried to evaluate what was best for us,” says Ken MacKenzie, UDFCD’s master planning program manager. “The Snyder Unit Hydrograph came the closest. We then calibrated it to local rainfall and runoff rates.”

From this work came UDFCD’s first stormwater modeling software, called Colorado Urban Hydrograph Procedure (CUHP). The original design was hand-calculated, as this was before the age of personal computers. Only mainframes were available then.

MacKenzie says the software has “gone through a number of changes, from Fortran to Fortran for PCs to a C+ version on diskette for PCs and then to a Microsoft Excel workbook. Microsoft Excel has some powerful Visual Basic programming capabilities built into it. Writing macros, which most people use it for, is only the tip of the iceberg.”

The current version of the software, coupled with the EPA’s Stormwater Management Model (SWMM) for routing, “is the only method we recommend for developing hydrology on a watershed level along the Colorado Front Range,” says MacKenzie, adding that even though the ­software is specific for the area with regard to rainfall and runoff rates, other communities have adopted it.

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About the Author

Margaret Buranen

Margaret Buranen writes on the environment and business.