Handbook for Predicting Stream Meander Migration and Supporting Software (2004) / Chapter Skim
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52.1 PROJECT DESCRIPTION AND OBJECTIVES Channel migration has important implications for the design, maintenance, and inspection of bridges and other highway facilities. Bend shifting or cutoffs upstream of a bridge reach can produce poor alignment of the channel approaching the bridge, high angles of attack, and an increase in vegetative debris from bank erosion.
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Braided rivers are high-energy rivers with abundant coarse sediment loads that feature multi-thread flow in subchannels (anabranches) ; mobile braid bars; and rapidly shifting, highly erodible banklines.
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7centrated between the bend apex and exit, leading to simultaneous lateral growth and down-valley migration of the bend. However, during high in-bank flows, the point of greatest attack moves downstream of the bend exit, leading to rapid bend migration downstream.
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From page 8... ...
Chute channels are associated with relatively high stream powers, abundant bed material loads, erodible banks, and high rates of lateral migration. 2.3.3 Characteristics of Meandering Streams The intensity of meandering is most often characterized by channel sinuosity, which is defined as the ratio of the channel centerline length to the valley length.
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From page 9... ...
9indicates that the greater erosion resistance of silt-clay banks results in tighter, shorter wavelength bends than those channels with less cohesive, easily eroded banks. Schumm has also demonstrated that changes to the weighted silt–clay index (M)
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From page 10... ...
10 Figure 2.3. Modes of meander loop development: (a)
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From page 11... ...
11 side of this range. At the lower end of the range, the decrease may be attributable to the large increase in resistance or a decrease in outer-bank radial force as RC/W falls below 2.
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From page 12... ...
predict the rate and extent of incremental channel shift as a result of meander migration. Aerial photograph comparison and frequency analysis techniques are provided to predict the potential impact of meander migration on highway facilities for specific classes of meandering channels.
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From page 13... ...
13 that develops across the neck of a meander loop (neck cutoff) or across a point bar (chute cutoff)
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