Maintenance Program Activities

by
Mark R. Hunter, P. E.
Chief, Maintenance Program

Routine Maintenance

Through the routine maintenance program $659,500 was spent in 1998 for mowing and debris pickups on approximately 218 different sections of drainageways within the District boundaries. This equates to a total of about 100 miles of drainageways in the Denver area where we performed routine mowing and debris pickup maintenance.

For 1998 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.

The overall goal of our routine maintenance work continues to be the on-going upkeep of urban drainageways to insure that they function properly as flood carrying facilities.

Restoration Maintenance

In 1998 the restoration program completed $1,428,000 of work. Restoration projects typically address isolated drainage problems where the solution involves small scale construction. One hundred individual activities were completed during the year. A major advantage of the restoration program is the opportunity to use it to react quickly to local drainage needs.

An example of reacting to a drainageway maintenance need occurred in Brighton, Colorado during the summer of 1998. City staff informed us that Line B, also known as South Urban Channel, needed repairs. Line B was originally improved by the City of Brighton and the District Design and Construction Program about 20 years ago. Changes in the upstream reaches of the creek coupled with natural processes caused sediment deposition to occur in the improved section. What was originally intended to be an urban passive-recreation corridor was becoming a marshy and mosquito-ridden area. The channel was wide and flat-bottomed with a riprap-lined trickle channel. The deposition was occurring in and around the trickle channel due to the frequency of the smaller storm events and the roughness of the riprap. Our work included removing the sediment as well as reshaping and resetting the riprap for much of the length of the trickle channel. Not all the problems were solved, however. This section of Line B is still awaiting an improved outlet to the South Platte River.

A similar opportunity to react arose in mid-1998 on what is called the Pinehurst Tributary to Bear Creek in southwest Denver. At a rear-yard location overland flow was captured by an inlet and pipe system. Because of its setting the pipe inlet frequently became plugged with debris. The result was that runoff could not enter the pipe and would back up enough that the water, in its obligation to seek the lowest point, would sweep around and through several homes. The final solution to this problem was not in a maintenance project but in capital improvements that would ultimately remove the homes from the floodplain. Such improvements had yet to be planned, designed and built. Recognizing that it could be years before such improvements would be made, project planners hoped to make short term changes to help the neighborhood. It was recommended that the inlet to the pipe be improved to increase the amount of water it let into the pipe. This fell within the work the Maintenance Program could perform. The inlet design and construction were completed within a couple months. While the development of the master plan for flood control improvements is still underway the improved inlet will now provide better water carrying capacity for the neighborhood than before.

Rehabilitation Maintenance

Twenty-eight projects were at various stages of design or construction during 1998. Those projects are listed in the accompanying table. Rehabilitation projects usually take the form of consultant-designed repairs that are intended to address severe problems that have occurred on a previously improved urban drainageway. By the end of 1998 the District will have spent about $3,030,000 on rehabilitative design and construction for the year. A few of the unique projects are discussed below.

Over the past two years we have reported on our project on Niver Creek in Adams County near the South Platte River. It has been a slow process but the result is a coordinated design for a new bridge, a rehabilitated open channel with drop structures, and an expanded trailhead park. The design has been completed and the work was recently publicly bid. With funding in place from several different sources construction of this project will soon begin. Deteriorated pipe, a concrete lined channel and an eroded channel will be replaced with a new bridge over Niver Creek, a restored open channel for Niver Creek and a trail-head park facility.

In Arapahoe county, just south of Dry Creek Road, Willow Creek had cut a 25-foot high eroded bank. About 2,000 feet downstream the creek entered the flood detention pool behind Englewood Dam. The flood pool had been experiencing aggradation for several years. The District's Design and Construction Program had a design underway to solve the severe erosion problem. Coupled with that design the Maintenance Program had the same consultant design a sediment trap upstream of the flood pool. This trap will reduce the amount of large sediments being deposited in the detention pond and will improve the quality of the water in the stream. The sediment trap should also help reduce the on-going muck removal that has been necessary to keep open the pedestrian trail under Dry Creek Road. Construction on this project began in November, 1998 and should be finished in the spring of 1999. This is a new area of work for the Maintenance Program. We will provide updates on this project as it is completed and comes into service.

A similar sediment trap is proposed upstream of the flood detention pool behind Holly Dam on Little Dry Creek. This project is on the north side of Arapahoe Road about one mile north of the sediment trap on Willow Creek mentioned above. Design for this project will get underway in 1999.

In last year's Flood Hazard News we reported that two large projects were underway on Goldsmith Gulch in the City of Denver. Both projects are situated on park land and both have benefited from a design partnership with participants from nearby neighborhoods, the Denver parks department, the consultant and the District maintenance program.

Within Bible Park Goldsmith Gulch flowed through a broad natural area. The exception to this meadow-like setting was that the creek had eroded a vertical-sided channel ranging from three to ten feet deep and 20 to 40 feet wide. The design partnership used the land afforded by the park to recreate a relatively natural riparian corridor for the stream. The recently-completed project created a meandering stream with shallow overbanks which made the stream more accessible and aesthetically pleasing to the park users. Thousands of wetland plantings were installed under this project. Late-season storms damaged some of the plant sites. The spring of 1999 will reveal how well these sites recover. Eventually we expect this project to be a remarkable restoration to an urban stream. The critical element was that there was enough land area to allow the design team to consider this type of project.

Within Cook Park, about one and one-half miles north of Bible Park, the erosion in the low flow channel of Goldsmith Gulch had created a steep-sided channel that is three to six feet deep. Although this was not as severe as the erosion in Bible Park the setting in Cook Park is an improved blue-grass multi-use area. This dictated that the channel configuration for Goldsmith Gulch be rehabilitated to be less of a threat to existing facilities such as pedestrian bridges and play areas. This project was bid in December, 1998. Construction should be complete by late spring, 1999.

Ralston Creek is an example of a drainageway that had been severely modified by the development process. It is now confined to an inflexible corridor where natural changes in the stream cross-section often result in unacceptable impacts to the adjacent landowners. Construction is now underway incorporating bank protection and drop structures to repair the damage and to keep the creek within its limited corridor.

West of Colorado Boulevard in Arapahoe County was a setting where Little Dry Creek passed through an open space area dotted with large trees. The creek had eroded a near-vertical bank that threatened a parking lot and a pipe and manhole for a large sanitary sewer line. The solution called for moving the toe of the steep bank back toward the creek enough so the slope could be rebuilt to a safer two -to-one gradient. A grouted boulder drop structure was installed downstream of the steep bank to reduce the erosive power of the creek and to protect the sewer line.

Barnum Lake on Weir Gulch at Federal Boulevard and 6th Avenue had filled in with so much sediment over the years that it had an average water depth of nine inches. The lake serves primarily as a natural habitat area and a stormwater detention pond. By its location it inevitably serves as a sediment trap as well. The Denver Parks Department designed a project to remove the accumulated sediment and restore the lake to an attractive wildlife habitat. Plans also included nature trails and fishing stations on the banks of the lake. The Maintenance Program participated in this project at two levels. Any sediment that was within the stormwater detention volume of the lake qualified for maintenance of a flood control facility. The Maintenance Program fully funded the removal of sediment that occupied the designed detention volume of the pond. Any sediment that was trapped within the permanent pool of the lake did not impact detention volume but did serve to improve the quality of the water in Weir Gulch. The Maintenance Program funded a part of the cost of removal of this sediment recognizing that improved water quality is a long-term benefit to the overall function of a drainageway.

New Staff Member

Jeff Fisher has joined the District as an Engineering Inspector in the Maintenance Program. Jeff holds a Bachelor's of Science Degree in Natural Resources from Ohio State University. His most recent work experience was with Drexel Barrell Inc. in Boulder Colorado where he was a Senior Inspector on construction projects. Prior to that he performed materials testing for a large pipeline project in Colorado and managed all phases of work for structural foundation improvements in Ohio. Jeff's favorite hobby is collecting old Keen Kutter tools.