HR: 10:50h
AN: H51F-03    [PDF]
TI: The Suspended-sediment Conveyor Belt in Humid Tropical Puerto Rico
AU: * Gellis, A C
EM: agellis@usgs.gov
AF: US Geological Survey, 8987 Yellow Brick Road, Baltimore, MD 21237
AB: The production, transport, and delivery of sediment from hillslopes to channels and to the sampling point in humid-tropical Puerto Rico can be visualized as a conveyor belt that is affected by hydrologic characteristics of the current event, previous events, and between events. In Puerto Rico a model of how the conveyor belt operates in four basins of differing land use (forest, pasture, cropland, and urban was developed using 3,096 suspended-sediment samples and 754 storm-generated runoff events collected from 1989 though 1995. Instrumented basin areas ranged from 3.26 km$^{2}$ to 19.4 km$^{2}$. Statistical analysis included multiple regression and principal components analysis. The suspended-sediment conveyor belt operates differently as sediment supply increases. In the forest and pasture basins, sediment sources are minimal, typically as landslides, and large storm-generated runoff events supply sediment to the channel where it is deposited and becomes the source of sediment for the next runoff event. Clockwise hysteresis loops are common in the forested basin and support the idea that the channel is a source of sediment. In the forest basin, runoff and rainfall occurring between events flush some of the sediment in storage, while in the pasture basin, rainfall and runoff occurring between events supply sediment to the channel. In the cropland basin, sediment sources increase, and large rainfall events supply sediment to the channel where it is flushed by the storm-generated runoff. Rainfall between events also supply sediment to the channel where it is flushed by high flow between events. In the urban basin with widespread sediment sources from construction activities, storm-generated events and high flows between events flush sediment from hillslopes and channels. Sediment is made available on hillslopes by construction activities such as land clearance and bulldozers. As sediment supply in a basin increases, channel hysteresis loops trend from clockwise to counterclockwise. Disturbance in watersheds draining fine grain soils will more likely exhibit counterclockwise hysteresis loops as sediment that is entrained remains in suspension longer, often peaking after the peak flow. The role of previous storm events in flushing sediment becomes more important as disturbance in a basin increases.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2003 Fall Meeting