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Influence of flow variability on floodplain formation and destruction, Little Missouri River, North Dakota

Jennifer R. Miller^1,* and Jonathan M. Friedman^2,

¹ Department of Forest, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, Colorado 80523, USA
² U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado 80526, USA

Correspondence: friedmanj{at}usgs.gov

Correspondence: *Present address: Metcalf & Eddy/AECOM, 1201 Peachtree Street, 400 Colony Square, Suite 1104, Atlanta, Georgia 30361, USA.

Resolving observations of channel change into separate planimetric measurements of floodplain formation and destruction reveals distinct relations between these processes and the flow regime. We analyzed a time sequence of eight bottomland images from 1939 to 2003 along the Little Missouri River, North Dakota, to relate geomorphic floodplain change to flow along this largely unregulated river. At the decadal scale, floodplain formation and destruction varied independently. Destruction was strongly positively correlated with the magnitude of infrequent high flows that recur every 5–10 yr, whereas floodplain formation was negatively correlated with the magnitude of frequent low flows exceeded 80% of the time. At the century scale, however, a climatically induced decrease in peak flows has reduced the destruction rate, limiting the area made available for floodplain formation. The rate of destruction was not uniform across the floodplain. Younger surfaces were consistently destroyed at a higher rate than older surfaces, suggesting that throughput of contaminants would have occurred more rapidly than predicted by models that assume uniform residence time of sediment across the floodplain. Maps of floodplain ages produced by analysis of sequential floodplain images are similar to maps of forest ages produced through dendrochronology, confirming the assumption of dendrogeomorphic studies that riparian tree establishment in this system is limited to recent channel locations.

Key Words: aerial photography • channel adjustment • dominant discharge • erosion • flood • plains cottonwood