HR: 1330h
AN: H33A-05    [Abstracts]
TI: Modeling Longitudinal Profiles and Downstream Fining in Large, Sand-bed Rivers
AU: * Wright, S A
EM: sawright@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001 United States
AU: Parker, G
EM: parke002@umn.edu
AF: University of Minnesota, 2 3rd Ave SE, Minneapolis, MN 55414 United States
AB: A well-known characteristic of many rivers is a decrease in the characteristic bed-sediment grain diameter (e.g. the median) in the downstream direction. This characteristic, often termed downstream fining, is typically accompanied by a downstream decrease in bed slope, i.e. a concave upward longitudinal profile. Two classical examples of these phenomena in large, sand-bed rivers are the lower Mississippi River, USA, and the middle Fly River, Papua New Guinea. In order to study the mechanisms that control longitudinal profile development and downstream fining in large, sand-bed rivers, we developed a numerical model capable of simulating these phenomena over space scales of hundreds of kilometers and time scales of thousands of years. A key aspect of the numerical model formulation is the ability to simulate a moving boundary at the downstream end, i.e. a delta prograding into standing water. This is important because this is one mechanism that leads to a concave upward profile and downstream fining. Other mechanisms studied through a series of model simulations include sea-level rise and tectonic subsidence. Various rates of sea-level rise (typical of the late Holocene) and tectonic subsidence were modeled in order to quantify their effects on the degree of profile concavity and downstream fining, with comparison to observations in several large, sand-bed rivers.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1655 Water cycles (1836)
DE: 1815 Erosion and sedimentation
DE: 1860 Runoff and streamflow
DE: 4558 Sediment transport
SC: Hydrology [H]
MN: 2005 Joint Assembly