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ERDC TR-04-1
associated with channel avulsions should be considered the norm, rather than the
exception, on anastomosing rivers.
Single-Thread Channels with Adjacent Floodplains
Single-thread, generally meandering channels with adjacent floodplains are
characteristic of humid climates but do occur in drylands (Fig. 11) (Graf 1988b).
They occur where a dependable water supply is present, as in allogenic rivers
(i.e. rivers that drain watersheds extending into more humid climates, such as the
Colorado River) (Tooth 2000). Meandering is more pronounced with vegetation
(Merritt and Cooper 2000), partially explaining why single-thread channels in
arid climates tend toward a lower sinuosity (Schumm 1961). Dryland perennial
rivers have morphologies similar to those known for humid regions (Cooke et al.
1993), where vegetation and more constant flow are able to stabilize banks and
form vertically accreting floodplain surfaces rather than laterally unstable
compound channels. Transmission losses (Reid and Frostick 1997) and debris
flow inputs from tributaries (Graf 1979, Webb et al. 1988) are unique
occurrences in drylands that may alter the characteristic perennial river form.
Decreasing width:depth ratios during large floods may compensate for the
decreasing discharge downstream along allogenic rivers (Deodhar and Kale
1999). To the extent that dryland perennial rivers mimic their humid-region
counterparts, a stable channel form may develop, and delineation of the OHWM
becomes easier.
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