BOARD01600

• Board Meeting Date: 9/24/2001
• Description: Flood Section - Inspection of South Platte River - Chatfield Downstream Channel Improvement Project
• Board Meetings - Doc Type: Memo

major exception is the native tree growth along the channel banks. The overall project has been
given an unacceptable rating because of the tree growth issues, although most of the individual
project features have received an acceptable or marginally acceptable rating this year.

At the request of the CWCB, the District has performed annual maintenance tasks along the
project reach. Such activities have included:
. Removal of non-native trees and trash trees from the channel bottom and other areas,
. Repair of drop structures and other riprap features,
. Removal oflarge flood deposits and other debris from the channel, and
. Removal of sediment and trash that blocks culvert outlets and hinders flap gate operation.

In 1999, the CWCB and District completed a joint effort to hydraulically model the project reach
of the South Platte River. This effort resulted from a meeting held in 1996 whereby the Corps
agreed to allow willows and trees to remain on the channel banks if the HEC-2analysis showed
no significant impact to the water surface profile due to increased roughness. The CWCB
expended funds to obtain new topographic mapping for the project reach (2' contour interval),
and the District expended funds to contract with ICON Engineering to perform the hydraulic
analyses. The cost of this effort was on the order of $100,000. The study was submitted to the
Corps for their review, and comments were returned to the CWCB. The CWCB and District
responded to those comments. The hydraulic model showed no significant impact to the water
surface profile as a result of willow and tree growth on the channel banks. No further actions or
decisions have taken place regarding the hydraulic model, however the Corps is currently taking
a second look at the modeling results.

PROJECT STATUS
At this time, the South Platte channel improvement project has received a marginally acceptable .,
rating from the Corps of Engineers. In the event of a flood disaster that damages the project, the
CWCB is eligible to receive emergency repair funds and assistance from the Corps' PL 84-99
program. It is imperative that the project receive an acceptable inspection rating within two
years, or else the project will become ineligible for federal assistance.

POTENTIAL SECTION 1135 PROJECT
The Omaha Corps has offered to participate in a Section 1135 project (Project Modification for
hnprovement of Environment) with the CWCB. The purpose of the 1135 program is to modifY
features or operations of previously constructed Corps projects to improve the quality of the
environment in the public interest. The non-federal cost share requirement for this program is
25% (in-kind services and lor cash). The non-federal sponsor's share of the cost is not payable
unless the project enters the construction phase.

Specifically for the South Platte River, an 1135 project could address two issues. The first issue
deals with a revision and update of the current operation and maintenance manual (O&M
Manual). It is proposed that the O&M Manual would be revised and amended to incorporate the
new concepts of vegetation management and environmental considerations. The second issue
deals with actual vegetation management along the project reach. Work could include removal
of non-native (and possibly some native) species of trees along the banks of the river, with
replacement trees added outside of the 100-year floodplain. We assume that an 1135 project
would bring the subject river reach back into compliance with Federal requirements. tI

Flood Protection. Water Project Planning and Financing. Stteam and Lake Protection
Water Supply Protection. Conservation Planning

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