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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)


Natural Resource Management

First Advisor

W. Carter Johnson


This research examined the Populus communities that have established on the novel reservoir delta forming at the confluence of the White River and Fort Randall Reservoir (Lake Francis Case), a mainstem impoundment on the Missouri River in South Dakota. The research included: investigation of post-dam channel and floodplain morphodynamics based on repeat cross section surveys; GIS mapping of time, space, and age dynamics of post-dam riparian woodland cover using historical aerial imagery; and a field study of woody plant characteristics in 35 cottonwood stands along a 120 km reach of the lower White River and its delta. Cross sectional surveys for the lower White River showed that the thalweg aggraded by as much as 12 m between 1954 (2 years post-dam) and 2011. Sediments accumulated in the form of a broad wedge that currently occupies the last 31 km of the White River valley. The mean slope of this reach decreased from 0.70 m/km in 1954 to 0.29 m/km in 2011. Riparian woodland cover on the expanding delta increased by nearly 50 percent from pre-dam (1948) to present (2012). Age structure also changed, from domination by older woodland in the pre-dam period to younger woodland in the post-dam period. Woodland established on young alluvial surfaces near the reservoir and farther upstream on abandoned agricultural land undergoing increased flooding and sedimentation. Field inventories in 2011 and 2013 determined that cottonwood forest stands were similar in woody plant structure and composition to natural stands along the White and Missouri Rivers. Plant species were arranged along an environmental moisture gradient spanning the length of the river-delta continuum; wetland affiliated species comprised a larger proportion of the flora in the downstream direction and non-wetland species comprised a larger proportion of the flora in the upstream direction. Pioneer forest establishment on reservoir deltas offers new opportunities to counterbalance losses of high biodiversity riparian ecosystems along the Missouri and other regulated rivers. Further study is needed to determine the contribution of reservoir deltas to biodiversity along regulated rivers, and how active and passive restoration could improve the establishment and survival of cottonwood forests over the long-term.

Library of Congress Subject Headings

Deltas -- South Dakota Reservoir ecology -- White River (Neb. and S.D.) Riparian ecology -- South Dakota


Includes bibliographical references (pages 222-244)



Number of Pages



South Dakota State University


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