South Platte

South Platte River Program Notes

by
Ben Urbonas, P.E., Chief, South Platte River Program

Maintenance Activities

Routine Maintenance
In 1999 the South Platte River routine maintenance included an equivalent of:

	9.5 miles of tree trimming and pruning along the river trail,
	6 acres of string trimming at access ramps and rest areas,
	73 miles of trail edge mowing, and
	199 miles of trash and debris pickup and removal along the river.

A total of 150 truckloads of trash and debris were removed from the river and taken to landfills. This removal volume, up 46 percent from last year, was achieved in part by studying statistical data pertaining to trash and debris accumulation patterns gathered over the past four years, thereby tailoring our removal program to maximize results.

For the third consecutive year we participated in the Greenway Foundation’s annual NIMBY Fest volunteer trash pickup, during which an additional nine truckloads of trash were removed. In addition, government personnel and volunteer groups picked up and removed trash from the river corridor throughout the year. Unfortunately, we do not have an estimate of the volume removed by them. Trash is also regularly removed from trash receptacles maintained by park personnel along all recreational trails.

Although routine maintenance is rarely noticed by the public, without it the South Platte River corridor within the District would take on an unkempt "look" and "feel." Routine maintenance is essential for the preservation of wildlife habitat and to provide the public with a more pleasant experience whenever visiting the many trail and pocket park facilities along the River.

Tamarisk Infestation.
The South Platte River downstream of 88^th Avenue in Adams County is experiencing rapidly spreading Tamarisk infestation. Tamarisk, also known as Saltcedar, is a juniper-type plant. It has crowded out the riparian growth along the banks of the many Western rivers, including the Colorado River in Utah, to a point that fishermen and even deer cannot get to the water through the dense brush.

In 1999 we started an eradication effort in hopes to check its spread. This proved to be very effective and eliminated existing plants on publicly owned lands. We will continue to monitor these areas for new growth. The worst of the infestation, however, is along the shorelines of old gravel pit lakes adjacent to the river located on privately owned land. As long as these Tamarisk colonies remain, the South Platte River corridor throughout northern Adams County and beyond will continue to be under the threat of new infestations.

Restoration Maintenance
In 1999 the restoration maintenance program again stabilized, rehabilitated, and revegetated several riverbanks that had suffered severe erosion in the past few years. The program also helped to repair damages to a recreation trail (i.e., maintenance access) along the river.

We continue to assist Denver Parks and Recreation Department with the replacement of old wooden pedestrian bridges across the river. The new steel bridges have 10 feet wide concrete decks and conform to ADA requirements. The bridge at Huron Street in south Denver is scheduled for replacement in January 2000. This project will also widen the tight trail curves approaching the bridge to make them safer and accessible by snow removal equipment.

The next bridge to be replaced will be near First Avenue (extended). This project is particularly challenging because one end is close to Interstate 25 and the other end constrained by limited channel right-of-way. Work on this project should start late in 2000.

This year over 4500 feet of badly eroded and degraded (i.e., trashed) riverbanks were cleaned up, regraded to a gentler slope, protected with buried rock riprap, and revegetated. All of our revegetation includes grasses, trees and shrubs native to this area. Some of the species used include Cottonwood, Sand Bar Willows, Chokecherry, Golden Current, Three-Leaf Sumac, Sage, and Rabbitbrush. These bank repair projects comprise the bulk of the restorative maintenance work performed by the South Platte River Maintenance Program.

The largest restorative maintenance project this year restored 1500 feet of badly eroded riverbank adjacent to the recreational trail and the Metro Wastewater Reclamation Plant (Metro) at 64^th Avenue and York Street in Commerce City (See Before and After photos). This project removed an old five-foot high berm at the top of the bank to restore a connection between the river and the adjacent lands. The construction and revegetation has been mostly completed. The area will now be planted with cottonwood trees, more willow and possibly other shrub in early Spring of 2000. This project was jointly funded by the District and Metro.


Before and after views of the Metro bank stabilization project.

The second phase of the joint District-Metro project involves the installation of a sloping grouted buttress to an existing sewer crossing that has developed into a six to eight foot vertical drop. The drop evolved as the South Platte River bottom degraded vertically over the last 15 years. Where once the river flowed without a drop and the sewer line crossing had over four-feet of cover, we now have a vertical drop. This has created a hazard to the public and a barrier to possible fish migration. This second project is being done at Metro’s request to make the existing drop safer for boater passage, more structurally sound and provide for fish migration. This project should be completed in January 2000.

Often severe bank erosions occurred in response to a single flood event. Because it takes time to obtain federal permits, perform engineering design and to contract for bank restoration work, it is sometimes necessary to immediately arrest fast eroding banks with temporary repairs under emergency permits. This is done by dumping clean concrete rubble or riprap along the bank during high water periods. When the high water recedes, usually in the fall or winter, the final bank restoration project can be constructed. At that time, the previously dumped rubble is incorporated into the final design.

Cooperative Projects with Private Property Owners

Two cooperative projects in Adams County will be constructed soon. One involves the stabilization of 1500 feet of an actively eroding bank that has moved over 500 feet laterally in the last few years. The property owner is very concerned with how much farmland is being lost and how the erosion is endangering an existing oil well.

The other Co-op project currently in design involves working with the Ready Mixed Concrete Company to clean up and stabilize an existing bank adjacent to future gravel mining. This bank work will consist of bendway weirs similar to the photos shown in last year’s Flood Hazard News. Both projects will be constructed on flowage and maintenance access easements dedicated to the District in exchange for the bank stabilization work.

Since the inception of the South Platte River Program in 1987, over 400 acres of easements have been dedicated in exchange for river restorative maintenance work. These easements allow the District to actively participate with local governments in preserving floodplain/riparian areas along the river corridor. Next year we hope to obtain an additional 60 acres of easement from CAMAS, Inc. from McKay Road to 104^th Avenue in Adams County.

Capital Improvement Projects

Upper Central Platte Valley Project
As reported in 1998, the preliminary design report for the Upper Central Platte Valley project has been published. The challenge that remains is to find $19,000,000 to construct this terrific river restoration project. Toward that end the City and County of Denver is exploring the possibility of funding through the U.S. Army Corps of Engineers river restoration program.

Globeville Area Project
Phases 1 and 2 of this project have been completed. However, before the benefits of this work can be fully realized, Phase 3 of this project will need to be built. The design for Phase 3 is now 95% complete and right-of-way is being acquired. Farmers Reservoir and Irrigation Company has objected to the design concept, which requires significant modification of its diversion dam. Because of this the construction of this project is now expected to begin toward the end of 2000. When completed, about 300 acres of urbanized lands in Denver and Adams County will have been removed from the regulatory 100-year floodplain. In addition, a major hazard to the public that may be on the river, such as tubers, boaters and trail users will have been eliminated.

Other News and Projects

Low Flow Channel Improvements
In 1998 we reported on a project to provide an improved low flow channel from 15^th Street through City of Cuernavaca Park. Most of the improvements have been completed. These include a series of boatable grade control structures between 19^th Street and the HOV bridge Ľ mile downstream, a low flow training channel jetties along Commons Park and another grade control structure at 16^th Street. These modifications should significantly improve the boater experience and safety in this reach of the South Platte River.

Master Plan in Adams County
Since late 1998 the District has been working with Adams County, the cities of Brighton, Thornton, Commerce City, South Adams County Water and Sanitation District and the Denver Water Department to update the South Platte River Major Drainageway Plan through Adams County. The consultant for this project, Camp Dresser and McKee has conducted a number of meetings with project sponsors to help define what issues and concerns about the river they have and would like to see addressed in the master plan. We received the draft Phase A report in December and now hope to have the project completed in 2000. This is a multi-objective planning project that is examining water quality, aquatic habitat, terrestrial habitat, open space, recreational needs of the sponsors, water resources development, gravel mining needs and activities, land development trends along the river, etc. on a reach-by-reach basis.

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