HR: 0800h
AN: H41B-0503    [Abstracts]
TI: Simulating the effects of hyperpycnal events on the stratigraphy of Poverty Shelf, New Zealand
AU: * Hutton, E W
EM: Eric.Hutton@colorado.edu
AF: Instaar, University of Colorado, 1560 30th St., Boulder, CO 80309, United States
AU: Kettner, A J
EM: albert.kettner@colorado.edu
AF: Instaar, University of Colorado, 1560 30th St., Boulder, CO 80309, United States
AU: Kubo, Y
EM: kuboy@jamstec.go.jp
AF: JAMSTEC, Center for Deep Earth Exploration, Yokohama, 236-0001, Japan
AU: Gomez, B
EM: bgomez@indstate.edu
AF: Indiana State University, Geomorphology Laboratory, Terre Haute, IN 47809, United States
AU: Syvitski, J P
EM: james.syvitski@colorado.edu
AF: Instaar, University of Colorado, 1560 30th St., Boulder, CO 80309, United States
AB: The hydrologic-transport model, HydroTrend indicates that suspended sediment discharge of the Waipaoa River, New Zealand increased from 2.3 to 15 Mt/y over the last 3000 years. Prior to the arrival of European colonists in the nineteenth century A.D., volcanic eruptions, natural fires and severe storms controlled erosion rates within the basin. Since then, clearing of much of the indigenous forest for sheep farming has caused suspended sediment discharge of the Waipaoa to increase by 850%. HydroTrend simulations indicate the Waipaoa was not able to generate hyperpycnal discharges before the arrival of European colonists. However, because of deforestation in the headwaters, suspended sediment concentrations of the Waipaoa are now able to exceed 40 kg/m³ during large flood events. The river density of these events is great enough to cause the manner by which sediment is transported from the river to change from a surface plume to a hyperpycnal plume. Although these hyperpycnal events are rare (recurrence intervals greater than 2 years), simulations suggest these events carry approximately one fifth of the total sediment load. Observational data of hyperpycnal flows are scarce as they often only occur during extreme weather events. Given the proper boundary conditions, these events have the potential to transport large amounts of sediment over the sheltered Poverty Bay shelf, and into the deep ocean. For this study, we have used HydroTrend results as input to the basin filling model, sedflux (coupled with the hyperpycnal plume model, sakura), to investigate the impact of these hyperpycnal events on the stratigraphy of the Poverty Bay shelf. We note that while some flood events generate hyperpycnal flows that are able to bypass the shelf, others are unable to ignite and deposit the bulk of their sediment on the shelf.
DE: 1847 Modeling
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting