South Platte River Program Notes

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

Local Initiatives Along the Platte

City and County of Denver
We reported in 1997 that the City and County of Denver launched a major South Platte River initiative. This effort continues and the District is working with Denver to implement the river restoration and improvement features of this initiative.

Adams County
We also reported in 1997 that Adams County began a comprehensive look at the South Platte River corridor as an open space and recreational resource. The District is now continuing with this initiative, using the information, and documents developed by Adams County and other project sponsors, to prepare a master plan for the river through Adams County.

Maintenance Activities

Routine Maintenance
In 1998 the South Platte River routine maintenance included:

Approximately 103 truckloads of trash and debris were removed and taken to a landfill. Local government personnel and volunteer groups picked up and removed additional trash from the river corridor. Trash is also removed from trash receptacles maintained by park personnel along all recreational trails.

Although this type of routine maintenance often is not noticed or recognized by the public, without it the South Platte River corridor would have an entirely different "look" and "feel." This type of maintenance, we believe, is essential for the preservation of wildlife habitat. It also provides a more pleasant experience for the public when visiting the many trails and pocket parks along the 41 miles of the South Platte River between Chatfield Dam and the Weld-Adams County line.

Tamarisk Infestation
The South Platte River downstream of 88th Avenue in Adams County is experiencing rapidly spreading Tamarisk infestation. Tamarisk is a juniper-type plant. It has virtually crowded out the riparian growth along the banks of the Colorado River in Utah, to a point that fishermen cannot get to the water through the dense brush.

In October we started an eradication effort in hopes to check its spread (see related article by Ken MacKenzie). We are not sure how effective we will be at eliminating this noxious plant. We are limited in access to publicly owned property and much of the infestation is along the banks of old gravel pit lakes adjacent to the river. In addition, the seed can be viable for several years and Tamarisk in cleared areas is expected to reappear. We will have to keep removing new growth for several years before this infestation is under control.

Restoration Maintenance
The 1998 restoration maintenance program continued to stabilize, rehabilitate, and revegetate riverbanks experiencing severe erosion. In addition, the program repaired erosion damages along the recreation trail, repaired and constructed river grade control structures and assisted with replacement of old wood pedestrian bridges.

Due to the high flow event on July 25th, estimated to be 13,800 cfs at 19th Street in Denver, the restoration maintenance activities increased significantly. At least 12 sites along the river in Denver and Adams County experienced severe erosion needing immediate attention, namely over 5000 feet of eroded banks which have to be stabilized and revegetated due to this high flow. In addition, the concrete trail along the river was undermined at several locations and required immediate attention.

One large restorative maintenance project completed this year consisted of four grouted-boulder grade control structures below 19th Street in Denver. These structures reduce and stabilize the grade of the river and provide for enhanced boater safety between the new City of Cuernavaca Park and soon to be constructed Commons Park.

The District is continuing to assist Denver Parks and Recreation Department to replace the rapidly deteriorating timber pedestrian bridges along the South Platte River. Two of these bridges were replaced this year, one at Grant-Frontier Park upstream of Evans Avenue and the other at Frog Hollow Park upstream of 8th Avenue. The new steel bridges have a wider concrete deck, making it easier to traverse; need less maintenance; and are more resistant to vandalism. They also meet ADA access requirements. Over the next two to three years we hope to continue to work with Denver to replace up to four more deteriorating timber bridges along the South Platte River. In 1999 we hope to replace the bridge at Huron Street, located downstream of Alameda Avenue.

Last year we reported constructing a bank stabilization project using the bendway weir (i.e. rock jetty) concept. This method utilizes low height rock jetties to redirect erosive currents on the outside of a river bend away from the eroding bank. So far, this concept has performed well (See the "Alternative Bank Stabilization Update" article in this issue).

Cooperative Projects With Private Property Owners

In 1998 two cooperative projects were completed. The first involved the bank cleanup, stabilization, and revegetation along 1,400 feet of properties owned by Albert Frei and Sons, Inc. and the McIntosh Farm Company, downstream of the Brantner Ditch diversion in Adams County. This reach of the river has been experiencing bottom degradation and related bank erosion for many years. Historically, river bank stabilization in this area has been attempted by the property owners by pushing large concrete pipe, cars, bed springs, etc. into and along the river - The Bigger the Better! Right? Wrong!

The combination of laying the bank back, armoring with a well graded buried rock riprap with extended toe, and native vegetation achieves much better results. It not only stabilizes the banks, but also cleans them up, improves their appearance and produces new and improved riparian habitat. The project was constructed by Frei on the flowage and maintenance easements dedicated to the District by both property owners. Work was jointly funded by the District and the property owners.

The second bank stabilization project took place adjacent to a gravel pit owned by Suburban Sand and Gravel Company in Adams County. The sand and gravel pit operator, Aggregate Inc., had reported several breeches of the berm separating the pit from the river during high flows the past few years. This project stabilized 1000 feet of bank using buried rubble and rock riprap and revegetation of the site. Work on this project was also jointly funded by the District and the property owners. In addition, the owners dedicated to the District a flowage and maintenance easement.

Revegetation of the bank included seeding with native grasses, mulching, live willow and cottonwood staking and the planting of native shrubs. In addition, since several large cottonwood trees had previously fallen into the river in this area, they were placed on the upper bank to enhance wildlife habitat. The before-and-after photos of this site illustrate the marked improvement of this badly abused riverbank. Comparisons that are more dramatic will be evident in the future when many of the recent plantings mature.

Two new cooperative projects are in the works for next year. One will involve working with a property owner to stabilize 1500 feet of an actively eroding bank, one that moved laterally more than 500 feet in the last 7 years, near 144th Avenue, extended, in Adams County. The other project will involve working with Ready Mixed Concrete to clean up and stabilize a bank adjacent to a new pit operation near 154th Avenue, extended. This project will also help preserve a nicely vegetated natural area adjacent to the river.

Capital Improvement Projects

Upper Central Platte Valley Project
As reported in 1997, we have been working with Denver and the Public Service Company of Colorado (PSCo) to develop and design the Upper Central Platte Valley Project. A detailed preliminary design is now complete and a separate article by Leo Eisel and Bryan Kolstad describes this plan. The real challenge now facing us if to find $17,000,000 need to implement this terrific river restoration project.

Globeville Area Project
The other ongoing capital improvement project along the river is located in the Globeville neighborhood in north Denver. Phases 1 and 2, for approximately 6,000 feet of the river, have now been completed. The final design of Phase 3 is nearing completion. We expect Phase 3 construction to begin in 1999. When done, a major hazard to kayaks, rafters and trail users will have been eliminated. In so doing, about 300 acres of developed lands in Denver and Adams County will have been removed from the 100-year floodplain.

Other News and Projects

Low Flow Channel Improvements
Early in 1997 Denver requested the District to take the lead in the design of low flow channel improvements starting at 15th Street and extending through Rockmont Park. The design has now been completed and some of the improvements have already been constructed by Denver and the District. The remaining low flow channel improvements will be completed by Denver in 1999 as a part of their Commons Park project. A series of boatable grade control structures and low flow training jetties will provide pools and riffles and a better defined low flow channel through this downtown reach of the river.

Master Plan in Adams County
The District has entered into agreements with Adams County, the cities of Brighton, Thornton and Commerce City, the 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 firm of Camp Dresser and McKee has been selected by the project sponsors to develop this new plan, which is now under way. The planning project is examining water quality, aquatic and terrestrial habitat, open space, recreation, water resources development, gravel mining needs, and many other issues affecting this river reach. We hope to have this multi-jurisdictional, multi-objective plan completed in 1999.