HR: 0800h
AN: H21G-0820    [Abstracts]
TI: Fluvial responses to environmental perturbations since the Last Glacial Maximum
AU: * Kettner, A J
EM: kettner@colorado.edu
AF: INSTAAR, University of Colorado, 1560 30th Street, Boulder, CO 80303, United States
AU: Syvitski, J P
EM: james.syvitski@colorado.edu
AF: INSTAAR, University of Colorado, 1560 30th Street, Boulder, CO 80303, United States
AB: The numerical model HydroTrend, that produces daily time series of water discharge and sediment load to the ocean, is applied to three Mediterranean drainage basins to: (i) simulate the water and sediment flux changes over time and (ii) determine the impact of potential forcing factors on sediment and water fluxes and how this impact varied through time. Climate (precipitation, temperature and glacier equilibrium line) and drainage basin (basin elevation, drainage area and reservoir) reconstructions of the Po, Rhone and Tet river basins over the last 21 000 Cal. years B.P. are used as input to the model. Although these rivers are located in the same climatic region and drain into the same sedimentary basin, there are predictable differences in the delivered sediment fluxes due to shelf geometry and more local climatic effects. Simulated sediment fluxes for the Po, Rhone and Tet rivers during the late Pleistocene were considerably higher compared to Holocene pristine sediment flux, with a factor 3.5, 2.4 and 2.4 respectively. For the Po and the Rhone rivers, deglaciation in the late Pleistocene is the main factor, responsible for these higher sediment fluxes. Drainage basin area change due to sea level rise is the main cause of decrease in sediment flux for the Tet River and to a certain extent for the Po River. Man-made reservoirs reduced sediment flux to the ocean for the Po, Rhone and Tet rivers over the last 3 - 6 decades with a factor of 1.3, 3.8 and 2.4 respectively. Fluvial responses to climate and basin variations are reflected in the peak flood discharge and sediment concentration curves, where present day water peak flood curves for all the three rivers are the highest in the last 21 000 Cal. years B.P. However, their associated sediment concentration curves show opposite results because of diminishing glacial area and the impact of reservoirs. The Tet River has the ability to generate hyperpycnal plumes although the occurrence frequency changes over time. Prior to 15 500 Cal. years B.P. the river system area was extended due to the low sea level, causing a less favorable regime to generate hyperpycnal events. Presently sediment trapping due to man made reservoirs alters the river ability to generate hyperpycnal events.
DE: 1807 Climate impacts
DE: 1834 Human impacts
DE: 1847 Modeling
DE: 1862 Sediment transport (4558)
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting