Maintenance Program

Mark Hunter, PE, Program Manager

The Urban Drainage and Flood Control District Maintenance Program budgeted a total of $7.4 million in 2007 to maintaining publicly-held drainageways in the Denver metropolitan area. Our maintenance work covers the spectrum of drainageway work. It includes debris pick-up and mowing, localized repair to damaged and eroded channels or detention facilities, and consultant-designed reconstruction of long reaches of deteriorated drainageways.

Most of our work involves publicly-owned open channel drainageways that have been improved in the past as part of a capital improvement project or a subdivision development. These open channels typically have native-grass-lined banks, riprap or vegetative erosion protection, and rock or concrete grade control structures.

Mowing and Debris Pick-up
For the year 2007 we awarded eight contracts for debris pickups and native-grass mowing under our routine maintenance program. Six of those contracts were awarded as renewals of the prior year contract. The value of each of these renewed contracts was adjusted to match the change in the regional Consumer Price Index over the prior year. The remaining two contracts were awarded through a competitive bid process in March.

Mowing and debris pick-up work was done on 294 different sections of urban native-grass-lined drainageways within the District's boundaries. The contractual value of the work through October of the year was $825,370. The table below summarizes the miles of drainageways within each county in the District on which we performed regularly scheduled mowing and/or debris pickup maintenance.

Construction Activities
Through October of 2007, $4.8 million of maintenance work has been performed under our various construction contracts. For that group of localized drainage repairs where the estimate of construction cost is less than $400,000 the smaller activities are directly awarded to individual contractors while the larger projects are bid among our group of eleven private “Drainageway Contractors” who have qualified for open-ended contracts with the District. A major advantage of work under the open-ended contracts is the ability to use them to react quickly to local drainage needs.

When project construction will cost more than $400,000 the work is designed by a private consultant and then put out for public bid to be built by a private contractor. These larger projects typically address severe problems that have occurred on previously improved urban drainageways. Through the first 10 months of the year 114 individual activities have been completed, are under contract, or are being designed. Our major projects for the year are summarized in the accompanying table titled “Status of Major Maintenance Projects for 2007.”

Channel Repairs
Southeast of Orchard Road and Monaco Way construction is underway on Greenwood Gulch to stop the vertical and lateral erosion. The project includes low flow drop structures to reduce the erosive power of the creek by reducing the longitudinal gradient of the channel. The neighborhood and vegetation are mature so the drainageway corridor is confined. As a result there was no room to build 100-year capacity drop structures.

High water on Massey Draw in 2004 caused flooding damage near Kipling Street. It also caused erosion damage to an unimproved portion of the channel near Wadsworth Boulevard well downstream of the area that experienced the flooding conditions. In between the two damaged areas the channel had been improved in the past and therefore received little damage. We have now repaired the downstream erosion damage using boulders for bank protection and drop structures to reduce the creek gradient.

This view of Massey Draw shows the tight corridor in which the boulder walls and drop structures were built

In last year's Flood Hazard News we detailed the succession of construction and erosion that has occurred on Goldsmith Gulch between Iliff Avenue and Yale Avenue over the last 25 years. The longitudinal grade appears to be flat enough, yet the stream has been prone to flash flooding with resulting erosion and formation of secondary channels. The recently completed rehabilitation provided a low flow channel that was reinforced for its full width with boulders or riprap. Overbank erosion protection along this narrow corridor was established through the use of rolled erosion control materials and natural vegetation. The parallel regional trail was also rebuilt.

Multi-purpose Projects
We continue to cooperate with local governments to fund multi-purpose projects.  Since drainageways and parks often share the same corridor the repair of damage can be a combined effort.  Grange Hall Creek in Thornton, Northglenn, and Adams County has received much attention over the years.  Thornton is enhancing its recreation center northwest of 108th Avenue and Colorado Boulevard and we are coordinating with them to add needed drop structures to the creek. 

Goldsmith Gulch before	Goldsmith Gulch after

The linear corridors provided by drainageways are ideal avenues for neighborhood parks and trails.  East of Ward Road in Arvada Ralston Creek slices through a park where erosion by the creek has exposed utilities and threatened the trail.  Our design is underway to regain the natural banks and meanders of the creek and to protect the utilities and trail.

A patch of indigenous prairie grasses and shrubs adjoins the proposed channel and trail work on West Harvard Gulch west of the South Platte River near the Yale Avenue alignment.  While we have been slowly moving forward with the right-of-way acquisition and final funding arrangements we have been able to protect the legacy vegetation area from the churning wheels of dirt-bikes.  The proposed project will restore and protect the currently entrenched channel and will provide a highly desirable trail link to the South Platte River corridor for the neighborhoods to the west.

A major purpose of drainageway maintenance is to reduce large unexpected expenditures in the future by taking care of small problems while they are still small.  Toward that goal we have developed some simple low cost erosion control techniques with the intent of controlling erosion in the short-term so thorough study and design can be completed for long-term regional solutions.  These ideas are being tried on Windmill Creek northeast of Centennial Airport.  We will report on this effort in the future.

Detention Ponds and Sediment Control
The City of Brighton has relatively flat topography, but as urbanization occurs sediment is still generated and carried by South Urban Channel (Line B).  At its confluence with the South Platte River the grade is even flatter and the sediment is deposited.  Recent sediment removal and channel regrading has established a more efficient low flow channel to carry the material.  The nearby trail, which was often under water and mud, was also improved to make it a more all-weather corridor.

Our successful sediment removal and vegetation thinning last year on a flat reach of Coal Creek near Centaur Village in Lafayette has expanded downstream.  The additional work involves more removal of excess material, but will also include the installation of three or four grade control structures to manage lateral erosion.
Since the completion in the late 1990s of the sediment trap on Willow Creek south of Dry Creek Road in Centennial we have removed about 1000 cubic yards of material at least once each year.  We realize the sediment capture volume for this facility is undersized for the basin, yet it is capturing the large grained material which would otherwise be deposited under the nearby Dry Creek Road Bridge or in the flood pool behind Englewood Dam.

Grade Control
The design is nearly complete for the rehabilitation of the 18-foot tall drop structure on Cherry Creek upstream of Hampden Avenue and Havana Street.  The design has beenexpanded to include recent downstream erosion that is migrating toward the structure.  The new drop structure will accommodate the deeper downstream channel as well as the design discharge from Cherry Creek Reservoir.

Seven miles downstream from the above drop structure is another high priority structure on Cherry Creek that is being rebuilt.  Immediately west of University Boulevard is an old 4-foot tall timber and steel H-pile drop structure.  It is being rebuilt as a sheet pile and grouted boulder facility.  The work includes re-setting the Cherry Creek trail under University to accommodate a 90-degree bend in the alignment.  The design phase, including easement acquisition by Denver, is done and construction is planned in 2008.

South Urban Channel before	South Urban Channel after

Open channel drainageways are sometimes in the form of a concrete-lined trough in order to narrow the footprint of the facility.  Through some public areas south of Kentucky Avenue in Aurora Westerly Creek is held in a concrete-lined channel.  We have coordinated with Aurora over the last few years in the difficult reconstruction of four drop structures in this channel.  Each drop is a cast-in-place concrete foundation and wall with the wall extending well below the grade of the concrete channel.