HR: 0800h
AN: H51C-0388    [Abstracts]
TI: Simulating the Effects of Natural Events and Anthropogenic Activity on Sediment Discharge to the Poverty Shelf, New Zealand during the late Holocene
AU: * Kettner, A J
EM: kettner@colorado.edu
AF: University of Colorado, INSTAAR, Campus box 450, Boulder, CO 80309 United States
AU: * Kettner, A J
EM: kettner@colorado.edu
AF: Delft University of Technology, Applied Earth Sciences, P.O. Box 5028, Delft, 2600 GA Netherlands
AU: Syvitski, J P
EM: james.syvitski@colorado.edu
AF: University of Colorado, INSTAAR, Campus box 450, Boulder, CO 80309 United States
AU: Gomez, B
EM: bgomez@indstate.edu
AF: Indiana State University , Geomorphology Laboratory, Terre Haute, IN 47809 United States
AB: The 2203 km² Waipaoa and 312 km² Waimata river basins annually deliver ~16 Mt of suspended sediment to Poverty Bay and the adjacent continental shelf. Much of this sediment currently is generated during frequent runoff events by gully erosion, which was initiated in the early part of the twentieth century when the headwaters were deforested and converted to pasture by European farmers. In addition to this disturbance, the c. 200 A.D. Taupo eruption, Polynesian arrival (c. 1300 A.D); short-term fluctuations in climate of a few hundred years duration, such as a Southern hemisphere counterpart to the Medieval Warm Period; and short-lived, high magnitude events, such as magnitude > 7 earthquakes and large floods- with a >10² yr recurrence interval have all influenced basin sediment yield during the past 3000 yr. We modeled the effect of these events on basin sediment yield using HydroTrend, which is a numerical model that creates synthetic river discharge and sediment load time series over long periods as a function of climate trends and basin morphology. HydroTrend accepts input based on daily meteorological station data (e.g., statistics of temperature and precipitation and their interannual variations), and basin morphometry derived from DEM analysis. Altitudinal variations across the basin were characterized using climatological records from four stations, with between 10 and 100 years of record. Climate and environmental change scenarios were imposed onto the meteorological data using the record of storm activity derived from nearby Lake Tutira, and by varying the vegetation cover (which influences the amount of rain reaching the ground surface that is converted to runoff). Both the modeled water and suspended sediment discharge exhibit good agreement with 25 years of observations from a gauging station located ~10 km from the coast. In the long term, our simulations suggest that, under the indigenous forest cover, a 30% increase in precipitation due to increased storminess causes a 5% increase in suspended sediment discharge. By contrast, the disturbance to the vegetation cover by ashfall during the Taupo eruption resulted in an 80% increase in suspended sediment discharge. The disturbance by Polynesian settlement and the earliest European clearances had a minimal impact, but the subsequent clearances in the headwaters caused suspended sediment discharge to increase by 850%. All these trends are replicated in the depositional record preserved on the middle shelf.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1807 Climate impacts
DE: 1847 Modeling
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005