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Maintenance Program Activitiesby
Routine Maintenance For 1999 we continued with the increased level of mowing and debris pickups on many urban drainageways. Most of the more urban drainageways now receive four to five mowings and debris pickups per year. Three to four mowings per year was inadequate for effective weed control and for overall appearance. Other drainageways we maintain are more rural in character. On portions of some of these drainageways we have taken the opportunity to reduce or eliminate our mowing activities. This has been done to encourage habitat and leave a more natural character in the drainageway corridor. For the calendar year we awarded seven separate contracts for routine work. Four of those contracts were awarded through an internal review of proposals submitted by potential contractors. The remaining three were awarded through a direct competitive bid process. Restoration Maintenance Nature dictates that as long as sediment is being carried by a stream some of that sediment will drop out when the stream expands into a quiescent pool. One of the on-going obligations created when detention ponds are built is to keep those ponds relatively free of accumulated sediment. We have removed sediment from two-dozen detention ponds over the last two years. It takes a continual effort to keep these flood protection facilities functioning as intended. We envision that it will be more difficult to carry out this type of regular maintenance in the future as the Clean Water Act regulations become more restrictive. We also repaired the trickle channels and outlet structures in three of those regional detention ponds. Over the years the City of Boulder has built erosion prevention features on rural sections of Boulder Creek east of the City. Some of these improvements have recently been damaged. Our work will repair the damage and reinforce the improvements. An earlier project by a federal agency had straightened portions of the creek alignment. We will also return some local sinuosity to the creek. In contrast to the work on rural Boulder Creek we are also doing repairs to the trapezoidal concrete channels in the Montbello Drainageways. There are nine miles of concrete channels in this portion of Denver. The concrete panels lining these urbanized drainageways tend to buckle from hydrostatic pressure or collapse as a result of being undermined. Ninety percent of these channels are squeezed into the median between the opposing traffic lanes. There is little room for creativity in repairing these confined linear channels. On the banks of the valley where Harlan Street Outfall discharges into Clear Creek the City of Wheat Ridge is building some playfields. The lower three hundred feet of Harlan Street Outfall needed repair as the result of severe erosion. Our funds for the channel repair were combined with Wheat Ridge money to reconfigure the outfall to address the erosion and to provide more useable area for sports. In a similar cooperative project we are combining funds with the City of Lakewood to accelerate improvements to McIntyre Gulch along Alameda Parkway. These channels currently have a longitudinal slope of about two- percent. Drop structures and erosion resistant materials will be used for these narrow channels. Rehabilitation Maintenance Over the past three years we have reported on our project on Niver Creek in Adams County near the South Platte River. Construction is now complete. The result is that the deteriorated pipes, the concrete-lined channel, and the eroded open channel were replaced by a new roadway bridge, a rehabilitated open channel with drop structures and a wetland bottom, and an expanded trailhead park. Shaw Heights Tributary joins Little Dry Creek at Sheridan Boulevard and 76th Avenue in Westminster. Upstream from that point Shaw Heights Tributary passes through a small park. Above that it is compressed into a narrow corridor between a railroad track and residential backyards. Design is underway to contain the backyard erosion and to replace the temporary erosion control measures that were installed to protect the railroad and a nearby sewer line. In last year’s Flood Hazard News we reported on the sediment trap that was being constructed on Willow Creek at Dry Creek Road in Arapahoe County. It was completed in early summer of 1999. Four months later we removed nearly 1000 cubic yards of accumulated sediment from the facility. We expect to need to clean it again in the summer of 2000. About a mile away a comparable sediment control facility is being designed for Little Dry Creek (not related to the Little Dry Creek mentioned above) at Arapahoe Road in Arapahoe County. This site is just upstream from the Holly Dam regional detention pond. The new sediment trap will serve as a forebay for the detention facility and is expected to simplify our sediment removal procedure. Three large projects, which included significant revegetation efforts, were completed in 1999. Two of them were on Goldsmith Gulch in the City of Denver; one in Bible Park and the other in Cook Park. The third project was on Greenwood Gulch at Holly Street in Greenwood Village. All three projects were situated on parkland or open space and benefited from the design efforts of landscape architects. Our climate does not always agree with our revegetation schedule and our desire for quick re-establishment of plant life. On each of the three sites we have had to return with contractors to replant or reinforce the vegetation we originally installed. Clearly, part of the problem is the power that the stream has to wash away new seedlings. But, the more important factor is our semi-arid climate. Limited and sporadic moisture typically dictates that it will take three years to get the plant community re-established on a given project site. South of Dry Creek Road in Arapahoe County the Jamison Tributary to Willow Creek flows through a naturally-contoured urban corridor. It is a small channel but the gradient is steep enough that several drop structures were originally built to control the grade. Five of the drop structures have been damaged or undermined by erosion. We are rebuilding the drops with grouted boulders and have designed a cutoff wall to be installed with each structure. The town of Erie is northeast of the City of Boulder and has been experiencing a recent surge in population growth. A tributary to Coal Creek drains the new developments on the southwest side of Erie. It flows to the north until it encounters a railroad track where the water simply ponds until it can flow between the ties and rails of the track. For this project we will participate with Erie in the funding to channel the water to the east, parallel with the railroad tracks, to an appropriate connection with Coal Creek. In the early to mid-1980s the Maintenance Program rehabilitated six drop structures on Cherry Creek between University Boulevard and Holly Street in Denver. We rebuilt all six of them as sloping riprap drop structures making use of the existing sheet pile as the cutoff wall for our new drops. Each of the rebuilt drops starting failing almost immediately. Areas of the riprap appeared to be undersized and, in general, riprap is only as strong as its weakest area. We have re-rebuilt four of them as grouted sloping boulder structures and will begin the fifth one in the spring of 2000. The City of Parker has been active in extending its trails system. On Cherry Creek near the Arapahoe County line and on Sulphur Gulch in Rowley Downs trail connections are being built. The Maintenance Program was able to help fund these projects because the trails in both areas will provide maintenance access that otherwise would not exist. Welcome to New Staff Member
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