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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Bar Height. In the relatively sediment-free environment found in the study reaches of the South
Platte River, it follows that high bars exist on the river bed only where the river is adequately
wide. The variation ofthe maximum bar height for the monitored cross sections (Fig. 2) is great.
In the wide river, bar heights are around six feet In the narrow reaches, rarely are they,greater
than two feet.

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5

10

15 20 25 30 35 40
Cross Section Number

45

50 55

Figure 2.

The bar height in all the monitored cross sections. The bar height is taken as the
difference in elevation between the top of the bar and the bed of the main
channel, each averaged over the period of monitoring.

The initial perception was that the prolonged spring runoff in 1995 had built the bars to a new
and higher level. An inspection of the change in maximum bars levels at the monitoring cross
sections (Table 2) does not support this perception. The freshness of the bar surfaces and the
scouring out of bar vegetation was the most obvious result, and not bar raising.

Six bars did not change top elevation between 1995 and 1996. Four cross sections were under
construction and two were not surveyed. The change between 1995 and 1996 of the remaining
41 bars in the surveyed cross sections follows. Twenty five bars gained 0.8 ft in height on the
average and 16 became lower, each by 1.0 ft, again on the average.

The bars at Cross Sections 1, 2, and 3 in the downstream Rural reach each changed greatly
during the 1995 spring runoff, most likely due to bar movement At the transect, the bars at
Cross Sections I and 3 lowered 2.9 and 2.8 ft respectively. At the other cross section, the top
of the bar was raised 2.0 ft.

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