PROJ00047

• Contract/PO #: C153490
• Contractor Name: Union Avenue Boat Chute 1987
• Contract Type: Miscellaneous
• Water District: 0
• County: Arapahoe
• Loan Projects - Doc Type: Feasibility Study

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HYDROLOGY

11-31

Where the Chatfield Dam outlet channel empties into the South Platte River,
there is a check dam of rocks which drops approximately 6 feet. There-
after, the river flows in its natural channel for which the bottom is 160
feet wide on the average. The high bank is approximately 7 feet high.

There is a sewer line encased in concrete across the river bed immediately
downstream from the C-470 bridge. The sewer line has been exposed due to
river bed and bank erosion. Thereafter, the South Platte River is eroding
its banks in places. The river has moved itself appreciably, probably
aided by the gravel mining operations. : Between 1964 and 1978, the maximum
lateral movement of the meander loops was approximately 900 feet. Vertical
degradation of the South Platte River bed was a maximum of six feet during
this same period.

The reach between C-470 and Columbine Valley is planned to remain in a
semi-natural condition as a floodplain park; however, bank stabilization is
a high priority. In this reach there have been two major drops with a
total drop of 14 feet. The slope between the drops is about 7.3 feet per
mile. The bank full width of the river is 264 feet with an average depth
of 6.5 feet, making the width to depth ratio equal to 41.

This bed erosion has been accompanied with bank erosion on both sides of
the river. Trees have fallen into the channel and a gravel pit has been
breached.

Immediately upstream of Columbine Valley the river bed has aggraded
approximately 3 to 4 feet due to the flatter hydraulic slope.

Between Columbine Valley and Union Avenue, the USACE has constructed a
stable channel, a channel that has a stable bed, drop structures, and