CSDMS 2016 annual meeting poster ScottDavid
Morphodyanmics of Intra-floodplain Chute Channels
Douglas Edmonds, Indiana University Bloomington Indiana, United States. edmondsd@indiana.edu
Abstract:
The formation of chute channels has been demonstrated to play an essential role in regulating river sinuosity and initiating the transformation from a single to multi-thread planform river geometry. Most chute channels occur within the active channel belt, but growing evidence suggests that chute channels can extend far outside of the channel belt, called intra-floodplain chute channels. The origin and function of these chute channels to the fluvial system is not clear. Towards this end we have initiated an empirical and theoretical study of floodplain chute channels in Indiana, USA. Using elevation models and satellite imagery we mapped 3064 km2 of floodplain in Indiana, and find that 37.3% of mapped floodplains in Indiana have extensive intra-floodplain chute channel networks. These chute channel networks consist of two types of channel segments: meander cutoffs of the main channel and chute channels linking the cutoffs together. To understand how these chute channels link meander cutoffs together and eventually create floodplain channel networks we use Delft3D to explore floodplain morphodynamics. Our first modeling experiment starts from a generic floodplain prepopulated with meander cutoffs to explore what conditions promote and suppress intra-chute channel formation. We find that chute channel formation is optimized at an intermediate flood discharge. If the flood discharge is too large the meander cutoffs erosively diffuse, whereas if the floodwave is too small, channel initiation does not occur. A moderately sized floodwave reworks the sediment surrounding the topographic lows, enhancing the development of floodplain chute channels. Our second modeling experiments explore how floodplain chute channels evolve on the West Fork of the White River, Indiana, USA. We find that the floodplain chute channels are capable of conveying the entire 10 yr floodwave (Q=1330m3/s) leaving the inter-channel areas dry. Moreover, the chute channels can incise into the floodplain while the margins of channels are aggrading, creating levees. Our results suggest that under the right conditions, chute channel formation can be extensive enough to create channel networks across the floodplain.
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