UPPER CENTRAL PLATTE VALLEY
RIVER RESTORATION PROJECT

by
Leo Eisel, P. E. and Brian Kolstad, P. E.
McLaughlin Water Engineers, Ltd.

The Upper Central Platte Valley reach of Denver's South Platte River extends for approximately one mile, immediately west of downtown, from 8th Avenue to I-25 and runs through residential, commercial, and industrial areas. Historically, this reach of the South Platte has been subject to flood damage, channelization, and destruction of fish and wildlife habitat. Residential, commercial and industrial areas are still threatened by the 100-year flood. Flood waters escape from the channel in this reach, flow north and east along the channel and surround Elitch Gardens and the area now being developed for the Pepsi Center.

The Public Service Company's Zuni Power Plant dominates this reach of the river visually, physically, and functionally. Its cooling water diversion dam is the sole remaining obstacle to boating the entire 10.5 mile reach of the South Platte through Denver. Water backup from the dam has replaced the river with a reservoir for nearly 1 mile upstream. The river banks in this reach are steep, making access difficult and impairing wildlife habitat. Much of the vegetation in this reach is non-native and in a degraded condition.

In 1995, Mayor Wellington Webb established the South Platte River Commission (Commission) to improve the river. Major goals established by the Commission include: reducing flood hazard, restoring fish and wildlife habitat, providing increased access to the river and providing more opportunities for recreation on the river and in the river corridor. Creation of the Commission has resulted in renewed focus on the Upper Central Platte Valley reach. A Task Force, led by the Urban Drainage and Flood Control District has been formed and has developed a detailed plan for restoration of the South Platte River in the Upper Central Platte Valley reach. The Task Force has representatives from recreation, fishery, wildlife, water and neighborhood interests and also includes the Public Service Company, Denver Housing Authority, U.S. Army Corps of Engineers, and the Colorado Division of Wildlife. The major goals of the plan developed by the Task Force include:

Flood damage will be reduced for residents and businesses in the one-mile Central Platte River Valley by widening and lowering the river channel. Overbank flows will be reduced downstream in the areas adjacent to Elitch Gardens and the Pepsi Center.

By removing the Zuni Power Plant dam and providing a closed loop cooling system to the power plant, fish habitat, adjacent wetland habitat and boating opportunities will be restored and improved.

Creation of a low flow channel with deeper pools in the meanders will restore and improve fish habitat.

The one-mile long recreation corridor along the west bank will be improved.

A One-Mile Long wildlife corridor will be created along the east bank of the South Platte River.

The park at the confluence of Weir Gulch and the South Platte River, immediately adjacent to the Sun Valley Community Center and the Sun Valley neighborhood, will be improved to provide greater access to the river and create better interface between that neighborhood and the river.

Removal of the Zuni Power Plant dam is possible because Public Service Company has agreed to a closed loop cooling system, which reduces cooling water demand from approximately 100 cfs to 10 cfs. The reduced demand can be provided through an infiltration gallery, located beneath the channel of the South Platte River, thereby eliminating the need for a dam.

The cost estimate for this project is approximately $17 million, which includes features for flood damage reduction, improved river access, restoration and improvement of fish and wildlife habitat, removal of the Zuni Power Plant diversion dam and replacement with a closed loop cooling system and improvements to make this reach boatable.

This project could be constructed in several phases, if necessary, to accommodate available funding. These phases could be further separated into several component projects. The phases would need to be constructed in order beginning with the furthest downstream reach (Colfax Reach) so that the downstream channel would be capable of accepting upstream flood flows.

Colfax Reach
(Lakewood Gulch to I-25)

Implementation of the project in this reach will result in a substantial reduction in flood hazard and improvements in fish and wildlife habitat. The Colfax reach work can be broken down into several components:

Zuni Reach
(11th Avenue to Lakewood Gulch)

Implementation of the project in this reach will provide the greatest flood hazard reduction benefits. Estimated costs include providing temporary diversion facilities for Zuni Power Plant and constructing the closed loop cooling system. This project could be further separated into several components including:

Sun Valley Reach
(8th Avenue to 11th Avenue)

Implementation of the project in this reach will provide improved access to the river for the Sun Valley Community Center and neighborhood. Components in this reach include:

1. Lower a 54-inch water line.
2. Widen the channel on the west side.
3. Develop improvements at Weir Gulch Park.
4. Create wildlife corridor on east bank.
5. Shape low flow channel and create meanders.
6. Replace existing pedestrian/bicycle with 10-foot wide trail.

Implementation of this project will represent completion of a key component in Denver's 10.5 miles of South Platte River.