The Platte to Park Hill stormwater project aims to solve “a legacy problem” in the Montclair Basin, the biggest basin in the city and county of Denver, says James Price, program manager for Matrix Design Group, Denver, the project’s coordinator. “This big area lost its outfall over the hundred years of building in Denver. It happened a long time ago, before we were sophisticated in how we planned our city and issued permits. The city just grew and the outfall probably wasn’t defined as readily as other channels.”

As the city developed and flooding grew worse, “the status quo was no longer manageable,” Price says. “Something had to be done, and the normal mitigation approach of raising the buildings or building something localized no longer made sense—it was too expensive, it was impractical. The right approach was to build a proper outfall so the system was much safer, more cost-effective and we could make it an asset to the city and an amenity.”

Denver hired Matrix in 2015, with Livable Cities Studio as a consultant, “to help do the development and finish the scoping,” Price says.

At one point, four separate projects had been initiated to build two large detention ponds and improve stormwater capacity. “We knew that if all of these public and private projects should try to do their work independently, they would come up with solutions that might work on a site-by-site basis but would not solve the bigger public need for a safe outfall,” Price says. Flooding and risk would persist, ultimately costing more than it would to create one larger project, he says. Matrix and the city and county of Denver focused first on unifying individual projects into a coordinated program.

“Our role was to help work at the mayoral office level to organize the team. It was too big for any one agency within the city—too complicated and nuanced for a typical public-works project, and nobody really was set up to do a $300-million program like this,” Price says.

Multiple Issues

Stormwater detention was one major problem. “We had to add over 200 acre-ft of detention to make the system work hydraulically, and there was no place to put that. We had to find an area where we could do that much detention,” Price says.

Soil and groundwater contamination was another concern. The existing Globeville Landing Outfall was a Superfund site where a large smelter of gold and silver operated around 1900. Heavy metals and asbestos in the soil and groundwater had to be abated at considerable and unanticipated cost to the project. At two locations in the stormwater system, water quality will be improved by daylighting about two miles of flow previously buried in pipes. The open-channel flow exposes the water to ultraviolet light.

One of the greatest challenges was organizing a big, multi-agency program that required five years to plan, design, finance and construct. At the same time, the team had to coordinate and communicate with all the affected neighborhoods.

“We felt we could not communicate enough,” Price says. “The project includes four parts, so the whole thing is about restoring an outfall for Montclair Basin that can continue to be connected to other projects in the future.”

The four projects are scattered around the city, and each has attracted its own controversy. The city’s departments of public works and parks and recreation and the roster of engineers and contractors performing the work say they have tried to meet community questions by being open to people’s concerns and accommodating them whenever possible.

“When we started in 2015-2016, we had to convince a lot of people that we weren’t just here to build something that’s gray and dark and very engineered, with tall fences and barbed wire, something that’s going to look ugly and be an impediment. Those were all the fears of the community, because they just didn’t know what we were doing,” Price says.

Now, with growing awareness of the public benefits and amenities, he says, “I think we’re in a really good place.”

Outfall Upgrade

The $80.4-million redesign and replacement of the multiphase Globeville Landing Outfall (GLO) was the logical place to start the program. Denver’s stormwater has long entered the South Platte River at this point, and a park and outfall have occupied the site for decades.

“It’s important to build downstream to upstream and take the capacity from the river upwards,” Price says.

Merrick & Co., Greenwood Village, Colo., redesigned the landing park and a new stormwater open channel. The Denver office of Kiewit Infrastructure Co. was the integrated contractor for GLO and allowed to bid on all phases, winning one of those.

Work on GLO began in late fall 2016, when Ames Construction, Aurora, Colo., installed pipes connected upstream by a large box culvert that required installation by a crane because of its size. Kiewit’s phase consisted of twin tunnels under heavy rail and commuter rail lines that encountered unexpected utilities.

The 39th Avenue project connects to Kiewit’s GLO segment and progresses from downstream to upstream in the Montclair Basin.

SEMA Construction Inc., Denver, holds the $73-million design-build contract for the 39th Avenue Greenway project and Park Hill Detention Pond. Denver’s Felsburg Holt & Ullevig is the design consultant.

“For the most part, the greenway area was a piece of abandoned railroad,” says Larry Walsh, project manager and SEMA vice president. “When the city acquired the property ... they decided to make it a functional piece and make it a one-mile-long linear park. What otherwise would have been a typical public-works project now became a parks project too.”

It was Denver’s first shared-street concept, he says, “a two-block piece in which pedestrians and traffic will be on a street that has no curb and gutter, and looks more like a plaza.”

To protect old homes in the neighborhood, Walsh frequently met with residents who were concerned about vibrations. Excavation on the greenway project also revealed a historic, triple-brick stormwater pipe intercepted by new box culverts, illustrating how seriously the area’s drainage system was overwhelmed.

Farther upstream, two golf courses are being modified to serve as detention basins. The Park Hill project is part of SEMA Construction’s 39th Avenue design-build contract, and both are under construction, says Ryan Crum, senior engineer for Denver Public Works. The Park Hill project is on a 25-acre permanent easement within a private golf course.

“We are building a detention pond that would help take on a 100-year event,” Walsh says. “We’re about 30% complete on the excavation of the pond.”

Residents have complained they paid a premium for properties overlooking the golf course but now will be viewing a detention pond. “I think the city is looking at potentially putting back some landscaping and some trees” to partially restore their view, he says.

The City Park Golf Course has been a city asset since 1913, popular for its view of the Front Range as well as for its recreational value. “We’re getting frequent [stormwater] inundation between the golf course and the Montclair Basin to the northwest of the golf course on its way to the South Platte River,” says Sam Stevens, DPW engineer and architect supervisor. A detention pond sized for a 10-year-flood event was slated in that area, close to the middle of the Montclair Basin.

Saunders Construction Inc., Centennial, Colo., is the design-builder on the $44.9-million project, working with iCon Golf Studio and golf course architect Hale lrwin and Johnson Nathan Strohe, Denver, the clubhouse architect.

Scheduled to reopen this summer, the City Park Golf Course redesign includes an updated 18-hole, par-70 course, a new clubhouse and maintenance facility and a reforestation program with a net gain of 500 trees. The new course integrates a natural water-treatment channel to enhance course playability.

It will temporarily hold and slow floodwater during major storms, providing additional protection for homes and businesses downstream. Designers say the grading of the new course maintains sweeping vistas and the park-like feel of the original course.

 

Construction is still underway on the 39th Avenue Greenway in Denver, a large storm-drain backbone system with a multi-use facility built alongside an open channel. “The Greenway is a meandering channel about a mile long, and it will have a lot of water-quality features along it,” says Sam Stevens, engineer and architect supervisor for Denver Public Works. “It didn’t have any pipe or any drainage prior to our project. It was the first stormwater infrastructure in this neighborhood.” When complete, the greenway will have parks and a multi-use trail that also will serve as a maintenance path. Operational completion, with drainage facilities functioning, is scheduled for September, with final completion in 2020.