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

Cross Section 4

Station 160+70 S. of Brighton Ditch Weir

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Cross Section 3

Station 129+25 N. of Brighton Ditch Weir

East Bank: Vertical, eroding slowly. Resisted somewhat by roots in the sandy soil. Since
1984, this bank has receded approximately 25 ft. Upstream and downstream the
bankline is poorly defined. The floodplain is grassed with a few large
cottonwoods. Behind is a levee of gravel-mining pit overburden.

West Bank: Stable sandy silt with a low, sandy benn being deposited by the 1995 flows on
and between old broken woOden piles (Spot Photos 3 and 4). Downstream, bank
erosion has been arrested with a small hardpoint of riprap (Spot Photo 2).
Timbers protrude from the bank (Spot Photos 5 and 6) indicating that at least part
of the bank is spoil from the construction of the Brighton Ditch to the west.
Upper bank is heavily grassed and there are large cottonwoods between the bank
and the canal.

River Bed: Stable bed. The three low-flow channels and the low, flat middle bar on the west
and the higher middle bar on the east are sand and gravel. The low bar is clean,
free of vegetation, while the higher one has willow seedlings. There is some
Urban Veneer in the low-flow channels. Upstream, there is Brighton Ditch
diversion weir with headgate on the west side. Downstream there is a very large,
low, flat, gravel and sand, middle bar.

East Bank: Eroding bare, vertical bank of stratified sandy clay on the outside of a bend.
There are concrete rubble hard points around and upstream from the bend (photos
7 and 8) but these are too widely spaced to stop 20 ft of bank loss since 1986.
The floodplain is grassed up to an old levee.

West Bank: Stable top but slope has been eroded from a flat one at the base to nearly
vertical. Material is cohesive fines with layers of fine gravel. The cross-section
marker is on top of the remains of an old levee. Gravel is being mined on the
floodplain on this side of the river. On the next bend downstream, the bank is .
being cleaned up, reclaimed, and stabilized using buried riprap with vegetation.

River Bed: Stable. Main channel with coarse gravel bed is against the east bank. Most of
bed is not visible due to turbidity in the water. On the west side there is a large,
high, sloping sand and gravel point bar, barren except for two clumps of willow
seedlings and one grounded cottonwood snag. The cross section is in a bend.

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