UW Sediment Dynamics Group

Research

Our group conducts research all over the globe. Since 2000, we have carried out studies in Italy, Papua New Guinea, New Zealand, Chile, Brazil, Hawaii, Washington, Utah, and Alaska. Read on for more information about present and past research projects.

Current projects

Elwha River, Washington

High-density flows coming directly from rivers or reconstituted on continental shelves occur infrequently, but likely control the cross-margin transport of particulates and associated geochemical components. Therefore, investigating these elusive phenomena is critical for understanding the fate of many materials in the ocean. Dam removal on the Elwha River provides a special opportunity to address the operational mechanisms and the resulting sedimentary signatures of high-density flows.

Funding source: National Science Foundation

People: Andrea Ogston, Chuck Nittrouer, Kristen Lee, Emily Eidam

Willapa Bay and Skagit Bay, Washington

Processes controlling transfer of fine-grained sediment within and between channels and flats on intertidal flats

To understand the source-to-sink sediment transfer from rivers to marine deposition, we must develop our understanding of the gateway between the land and ocean -- shallow-water regions spanning the tidally influenced river to the inner shelf. Here, the processes that transport and package sediment in suspension undergo dramatic changes. Tidal flats represent one type of environment found in this shallow-water realm. The transport and deposition of fine-grained sediment varies over the global range of tidal flats, which consists of systems that predominantly import or export sediment, yet our understanding of why these differ is limited. This project seeks to explore: 1) local transfer of sediment between the water column and seabed in both channel and flat environments, 2) the environmental linkages, or exchange of sediment, between channel and flat environments, and 3) place those in the long-term cycle in relation to river discharge, wind, and wave forcing.

Funding source: Office of Naval Research

People: Chuck Nittrouer, Andrea Ogston, Kristen Lee, Katie Boldt, Dan Nowacki

Waipaoa River Shelf, New Zealand

Formation, reworking and accumulation of sedimentary deposits, Waipaoa Rver Shelf, New Zealand

This research examines dispersal processes and sediment dynamics that control strata production on the Waipaoa River margin, New Zealand, a MARGINS Source-to-Sink (S2S) focus site where discrete event beds have been found. This research combines numerical modeling of sediment dynamics, sediment-transport observations, and time-series coring with high-resolution sampling. A hydrodynamic / sediment transport model for the continental shelf is being developed to examine event- and seasonal-timescale dispersal and deposition. Seasonal variations in sediment transport and deposition across the Waipaoa River shelf are being studied during three ~4-month deployments of three near-bed tripods. During instrument site visits, shallow seabed coring is being conducted to reveal recently deposited strata using X-radiography, sedimentology, macrofaunal-density and radiochemistry.

Funding source: National Science Foundation

People: Andrea Ogston, Rip Hale

Patagonian Chile

Description coming soon

People: Chuck Nittrouer, Katie Boldt

Lake Chelan, Washington

Geologists have long recognized the importance of both river deltas and deep-ocean sedimentary systems as major sinks for large quantities of land-derived sediment, and as important components in the integrated source-to-sink transit of terrestrial sediments. Relatively few studies, however, have directed their attention at the linkage between the two, despite the fact that deltaic dynamics are almost always intimately related to deep marine sediment transport systems. This project examines the relationship between deltaic and deep- water sedimentation in Lake Chelan, WA, where the external forces acting on the system are relatively well constrained, and the river is directly linked to deeper water.

Lake Chelan sits in a fjord-like basin most recently scoured by a combination of the Chelan Glacier and Okanagan Lobe of the Cordilleran ice sheet during the Last Glacial Maximum. Lake Chelan sits 335 meters above sea level and reaches a depth of nearly 450 meters. The northern end of the lake is fed by the Stehekin River, which has produced a delta that has prograded some four kilometers in the last 9000 years.

In summer 2010 we completed bathymetric and sub-bottom surveys of the northern five kilometers of the lake. We also collected lake bed grab samples and gravity cores for grain size and geochemical analysis in order to characterize the transport and fate of sediment near the Stehekin Delta. The bathymetric and sub-bottom surveys reveal large-scale bedforms on the lake floor, likely the product of density currents produced during high river flows or as a consequence of failure on the delta front.

Funding source: University of Washington Royalty Research Fund

People: Chuck Nittrouer, Aaron Fricke

Wave-supported gravity currents

Laboratory study: Sediment transport in wave-supported gravity currents

A number of recent observational studies on continental shelves have observed high rates of cross-shelf transport in thin layers of highly concentrated fine-grained sediment. These gravity currents are sustained by the combined action of their negative buoyancy and supplemental shear stress provided by surface waves. Wave-supported gravity currents (WSGC) have been identified as an important mechanism for cross-shelf sediment transport on many shelves, yet our understanding of WSGC is limited to observational studies that cannot resolve the velocity or density structure within them.

The goals of this work are to determine the structure and transport in WSGC using a combination of laboratory experiments and prior field observations. The laboratory experiments are being conducted in a 5-m long sediment/wave flume constructed expressly for these experiments and proven to realistically reproduce conditions in the oceanic wave boundary layer. Evaluation of the laboratory results will be guided and motivated by field observations of such flows in three shelf systems (Eel and Po River margins, and Gulf of Papua).

People: Andrea Ogston, Alex Horner-Devine (UW CEE), Abbas Hooshmand (UW CEE)

Amazon Tidal River, Brazil

Description coming soon

Taiwan

This project was designed to characterize sediment accumulation in a submarine canyon with no major river source on an active continental margin. In collaboration with several Taiwanese scientists, we investigated the effects of a 2006 earthquake and 2009 typhoon in Fangliao Canyon, SW Taiwan. The work was funded by the US NSF and the Taiwan NSC, through the EAPSI fellowship. We found evidence of gravity flows generated by the earthquake and storm processes, through the investigation of a series of short (<50 cm) sediment cores. We used a suite of textural, radiochemical, and geochemical tracers to identify events, and attempt to determine the specific type of gravity flow responsible. This research emphasizes the importance of gravity flows on sediment transport, as well as the role that seemingly dormant submarine canyons can play as conduits for material from the terrestrial to deep-marine environments.

Funding source: National Science Foundation, Taiwan NSC

People: Chuck Nittrouer, Rip Hale

Molokai, Hawaii

Predictions of turbidity due to enhanced sediment resuspension resulting from sea-level rise on a fringing coral reef: evidence from Molokai, HI

The UW Sediment Dynamics group has been involved in the USGS Coral Reef studies on the Molokai, HI reef flat focusing on the evaluation of sediment-transport conditions, mechanisms, and impacts on depositional processes, and ultimately coral reef health. A specific goal of this work is to evaluate the sedimentary processes in light of projected sea-level rise. Discussion about effect of climate change on coral reef health and sustainability has largely focused on the effects of rising sea-surface temperature. However, increased sedimentation has also been correlated to coral stress and bleaching. The presence of suspended sediment may stress corals by reducing incident light levels, and moreover, particles that settle on coral surfaces interfere with photosynthesis and hinder feeding. The effects of increased water-surface elevation on coral reefs can be varied, and include increased circulation due to broader interaction with offshore water and changes in exposure to dissolved and particulate matter. Increased water-surface elevation will also change rates of erosion, resuspension and transport of terrigenous sediment on fringing reefs, and these impacts on turbidity are explored in this study.

People: Andrea Ogston

Puget Sound Beaches

Description coming soon

Recent projects

Gulf of Papua

Processes controlling depositional signals for environmental change in the Fly River sediment dispersal system: Mechanisms and rates of shelf clinoform development

This study was part of MARGINS Source-to-Sink (S2S) investigation of the Gulf of Papua, which is a foreland basin receiving large quantities of siliciclastic sediment. The energetic character of the setting imparts strong sedimentary signals to the fate of particles in its dispersal systems. The largest of these is the Fly River, which drains the rain-drenched highlands of Papua New Guinea. Its fluvial load enters the gulf, where tidal currents are strong and the variability of winds, waves and circulation is driven by seasonal changes from trade-wind to monsoon conditions. The wet-tropical setting causes river discharge to be relatively constant during most years. However, the proximity to the equatorial warm pool intensifies the impact of El Nino periods, when rainfall is dramatically decreased and so is river discharge.

The Gulf of Papua provided a valuable opportunity to study continental-shelf sedimentation, because it has a rich assortment of active processes and preserved stratigraphy. The focus of this investigation was on active sedimentation associated with the clinoform found on the inner and middle shelf, and the relationship of this sedimentation to the rest of the dispersal system.

Funding source: National Science Foundation

People: Chuck Nittrouer, Andrea Ogston, Dick Sternberg