Date Awarded

2003

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

John D. Milliman

Abstract

To estimate delivery to the coastal ocean, a global river database was assembled. An estimated 35,000 km3 of freshwater, 4 * 10 6 tonnes of dissolved solids and 18.6 * 106 tonnes of suspended sediment are delivered annually. The global delivery of fluvial water and sediment, both suspended and dissolved, is dominated by Southeast Asia, due to the unique climatic, geologic and geomorphic character of the rivers in this region. Over 30% of the global freshwater and dissolved solid discharge, and an astounding 70% of the suspended sediment originate in this region. The Salinas River, central California, was the focus of an in-depth study on the controls on sediment delivery from a small, semi-arid watershed. This river discharges into the Monterey Bay an average of 0.4 km3 of water and 3.3 tonnes of sediment annually. Basin-scale control on the discharge of the river is dominated by the underlying geology as well as the anthropogenic changes to the watershed. Despite the altered nature of the Salinas River, the fluvial discharge is dominated by short-lived meteorological events. Large flood events on the Salinas River almost entirely correlate with El Nino events. However, not all El Nino years produce flood events. It was shown that the probability of a large flood on the Salinas River is determined not only by the presence of El Nino conditions, but also by the interaction between the Pacific Decadal Oscillation and the ENSO. The coinciding of warm phases of both of these large-scale phenomena produces significantly higher annual discharges than any other combination of the climatic phenomena. The Monterey Bay is bisected by a submarine canyon, restricting the shelf space and creating 2 separate sedimentary environments. The southern shelf bypasses most modern fluvial sediment to the canyon, whereas the northern shelf stores most of the sediment delivered. The estimate of Holocene sediment discharge from the rivers and creeks of the bay indicate that >60% of fluvially delivered sediment is lost to the canyon and deep ocean. The transport pathways of this removal are currently unknown, but hyperpycnal flow from the mouth of the Salinas River is hypothesized.

DOI

https://dx.doi.org/doi:10.25773/v5-m27h-qr85

Rights

© The Author

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