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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INTRODUCTION

In the Denver metropolitan area, the stability of the South Platte River is of concern. Any river
movement, whether up and down or laterally, affects many private and public properties and can
threaten, damage, or destroy the existing infrastructure such as utility lines, hiker and biker trails,
bridges, and adjacent roadways. In 1983, the Urban Drainage and Flood Control District had
a stream stability investigation made of the South Platte between Baseline Road and Chatfield
Dam (Stevens 1983) and had produced thereafter the Master Plan for orderly development along
the river (Wright Water Engineers 1985).

In 1986, Urban Drainage began a program of monitoring changes in the South Platte River bed
levels and banks. The program included an initial geomorphic evaluation (Stevens 1986) and
was then followed up by annually resurveying cross sections at a number of fixed locations
along the river. Initially, 30 cross sections were established between State Highway 7 at
Brighton and 58th Avenue in Commerce City. In later years, more sections were added, first
in Denver and then farther upstream in the southern suburbs up to Highway C-470. There are
now a total of 53 permanently marked cross sections. The morphology data of these cross
sections are in Tables 1 and 2 following; the 1995-1996 winter season photographs of the
sections are in Appendix A; and the cross sections are plotted in Appendix D.

The information and opinions presented in this report follow on the basis of the previous stability
study and the annual monitoring of the river cross sections. The surveys have been evaluated,
ground photographs taken in 1986 and 1996 have been compared, and visual evaluations were
made in the field. The reader is also invited to. look at the photographs in Appendix B. These
illustrate certain features of the South Platte River that are surmised to be of interest.

GENERAL

The South Platte River though the Denver metropolitan area had been classified as either Rural,
Suburban, or Urban (Stevens 1983). That is, the river takes on different appearances depending
on the developments around it. The categorization is expanded and continued here. The new
member is the Engineered river. The characteristics of each member are briefly described as
follows.

Rural River

. The river is not straight but meanders somewhat through its floodplain. Sinuosity is
1.26.
. The river is free to move laterally by eroding one bank and building the other.
. As a result oflateral movement, the river can have one high and one low bank
. The river is wide and shallow, with sand, gravel, or cobble bars.
. Some bars are vegetated with pioneer weeds, grasses, and willows.
. On some banks, the natural succession of vegetation still exists.
. There is evidence of plentiful wildlife.
. Works of humans are few.