FLOOD02337

• County: Statewide
• Community: State
• Stream Name: South Platte River
• Basin: South Platte
• Title: Geomorphic Assessment at Surveyed Cross-sections South Platte River
• Date: 6/1/1996
• Prepared For: UDFCD
• Prepared By: Michael Stevens
• Floodplain - Doc Type: Floodplain Report/Masterplan

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MASTER PLAN

The guidance offered on river morphology for the development of the 1985 Major Drainageway
Planning report for the South Platte River is still valid. It envisaged the ideal river, relatively
free from maintenance and befitting of what such an alluvial river wants to do under the imposed
developments. That advice was used in part in developing this first Master Plan.

A revision of the Master Plan is appropriate. In almost all cases, it is impractical to have the
major flood channel of the river in any place other than where it is now. There has been a large
investment in infrastructure along the river as well as on the adjacent floodplain. These have
to be accommodated as well as the needs of the river.

The South Platte has adjusted to more frequently occurring lesser but longer flood flows,
creating more bars and sinuosity in its low-flow channel than would be needed for higher and
sharper annual floods. This added sinuosity means more opportunity for bank erosion, being that
the bank on the outside of each meander bend is a candidate for erosion.

The river bed has not degraded to any extent in the last nine years in the Rural reach.
Degradation was evident 10 years ago and was expected in all reaches of the metropolitan area
after the construction of the Cherry Creek, Bear Creek, and Chatfield Dams. There are enough
old and new grade-control structures in the Urban and Suburban reaches and the floods have
been mitigated enough so that no more serious degradation has occurred here in the South Platte.
The amount of bank erosion in the rural reach has supplied enough sediment to the river to
mitigate some of the degradation tendencies. Any increase in bank protection or an narrowing
of the river in the Rural reach could offset this existing sediment balance between supply and
transport capability. Then, more grade-control structures would be needed.

OTHER OBSERVATIONS

Need for More Water. In parts of the year, the South Platte River flow is very low from
Chatfield to the Metro Wastewater Treatment Plant near Interstate Highway 270. The water has
been diverted out by those holding the water rights. What is left is not of the highest quality.
Littleton has posted a notice in South Platte River Park that it is in the process of obtaining the
right for 75ft'/s to enhance recreation and aquatic life in its section of the river. In a 1996
luncheon address to planners, landscape architects, and engineers, Mayor Webb of Denver
addressed the same issue saying that Denver wanted to purchase some water rights for the
benefit of the South Platte River environment

Need for Better Water. The Metro Wastewater Reclamation District is reconstructing the reach
of South Platte River upstream of 88th Avenue to improve the quality of water that has been just
returned to the river. The new reach will provide more aeration of the water. In places, the
river itself does undertake to do the same with its riflles and diagonal bars (Fig. 8) in a most
pleasing manner.

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