HR: 1340h
AN: H53D-0517    [Abstracts]
TI: Cycle of Waterfall Morphology and Retreat on Tributaries of the Niobrara River by Valentine, Nebraska
AU: Mason, L J
EM: len.mason@phwllc.com
AF: Pastor, Behling, & Wheeler, LLC, 2000 S. Mays, Suite 300, Round Rock, TX 78664 United States
AU: * Pederson, D T
EM: dpederson2@unl.edu
AF: University of Nebraska-Lincoln, Department of Geosciences 214 Bessey Hall, Lincoln, NE 68588-0340 United States
AB: Waterfalls on the spring-fed tributaries of the Niobrara River by Valentine, Nebraska are known for their convex morphology. Erosion rates are much greater on either side of the waterfall as compared to the waterfall face. The resulting protrusion of the waterfall face is continually wet through all seasons because the tributaries are spring fed. Slope weathering processes of the Rosebud Formation (siltstone that makes up the cliffs in which the waterfalls are developed) are predominantly controlled by freeze/thaw and wet/dry cycles. These processes are minimized under the waterfall face which is continually wet. Examination of over 200 waterfalls shows a cycle of waterfall development. At some point the waterfall face convexity increases to the point that most streamflow is diverted to either side exposing portions of the waterfall face to increased weathering. The increasing convexity also causes the face to become unstable with subsequent collapse. With collapse of the waterfall face, rapid erosion occurs with the development of a flat or horseshoe upstream form with the water plunging to the base of the falls rather than running over the face of the falls. Over time with protection of the new waterfall face by running water and greater rates of weathering on the sides a new convex form develops thus completing the cycle. It appears that incision of the Niobrara River triggers the development of new waterfalls which migrate up tributary. Many tributaries have a sequence of waterfall faces at increasingly higher elevations. Rates of seasonal retreat on the adjacent alcoves have been determined using sediment collection systems. This gives a measure of the rates of waterfall retreat.
DE: 1815 Erosion
DE: 1818 Evapotranspiration
DE: 1824 Geomorphology: general (1625)
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: Fall Meeting 2005