Tidally-influenced fluvial zone (TIFZ)

All rivers across the globe that exit to the ocean contain a zone, which can be 100s of kilometres long, which is transitional between river and tidal environments (termed here the Tidally-Influenced Fluvial Zone, or TIFZ). This zone is one of the most complex environments on the surface of the Earth because it is an area where both river flow and tidal currents are significant, and these competing forces vary daily, seasonally and annually.

These regions are important to humans and form some of the areas of highest population density: they are strategically important in the present day because these zones are at the interface of competing demands for shipping, aquaculture, land reclamation and nature conservation. In order to better maintain, manage and protect these fragile zones, we must understand how and why these regions change and what factors control such change.

Additionally, the sediments of ancient TIFZs may contain significant volumes of hydrocarbons which are increasingly the target for many energy companies. For example, the Athabasca oil sands form the largest petroleum deposit on Earth and these bitumen tars are locked up largely within ancient TIFZ sediments.

We need to understand what controls the geometry and internal characteristics of these TIFZ sediments and thus plan efficient and maximal hydrocarbon extraction strategies.This three-year research project, funded by the UK NERC, began on 1 December 2010 and uses the Columbia River Estuary, USA to examine the morphodynamics and sedimentary deposits of this complex environment. Knowledge of both modern and ancient TIFZ environments is enhanced by a detailed quantification of the water flow structure in these areas, how such flows transport their sediment and critically how the form (or morphology) of these environments changes through time.

This project uses integrated field and mathematical modelling techniques to achieve a step-change in our understanding of the TIFZ. We will use techniques that yield unrivalled high-resolution datasets of bathymetry, flow, sediment transport and sedimentary structure that will then be used to construct and validate new numerical models of the TIFZ. This will ultimately allow evaluation of key unknowns with respect to the TIFZ, such as how such environments evolve under changing scenarios of tidal and fluvial contributions associated with sea-level change, and whether it is possible to differentiate between 'fluvial' and 'tidally' influenced deposits. Such results will also help us recognise these changes within ancient sedimentary successions.

Specific objectives are:

Quantify the bed morphology of the TIFZ, identify the principal bedforms and track the development of bars through use of historical data and production of repeat high-resolution DEMs.

Quantify the 3D flow field, bedload and suspended load transport rates and grain size over and around key bars, on flood, ebb, spring/neap tides and the freshet.

Determine the relationships between flow structure, sediment transport, bedform dynamics, bar morphology, and their dependence on different fluvial and tidal flows using Delft3D with boundary conditions derived from 1 and 2.

Establish the typical facies type and thickness, frequency and spatial distribution of different elements of the alluvial architecture of large bars in the TIFZ.

Distinguish the diagnostic structures of fluvial, fluvial-tidal and tidal-fluvial deposits across and down the TIFZ.

Adapt and apply Delft3D to the TIFZ to simulate channel and bar evolution over time periods of days, years and decades and produce the preserved stratigraphy for comparison to data from 4.

This project is based on the Columbia River Estuary, which forms the border between Oregon and Washington States in NW USA. An ~80 km2 study reach upstream of Tongue Point is the focus of detailed measurements and the channels between Port Westward (formerly Beaver Army Terminal) and downstream of Astoria are being surveyed to provide additional bathymetry and boundary conditions for the numerical modelling.

The Columbia is the:• 2nd largest river in the USA• drainage area of 660 480 km2• mean discharge of 7280 m3 s-1• sand-bedded in the TIFZ with negligible clay

The Columbia River is tidally-influenced for 160 km upstream of Portland but tidal energy is only significant in the lower 40-50 km downstream of Wauna. Tides in the Columbia River Estuary are of mixed diurnal and semidiurnal type with the semidiurnal wave being 1.5 to 2.1 times larger in amplitude than the diurnal wave.

The semidiurnal predominance increases in the upriver direction and the spring tidal range is 3.6 m with a large freshwater discharge. Peak river discharge occurs through spring snowmelt and from major winter subtropical storms. The Columbia River is regulated upstream of Portland and dredging occurs in the main navigation channel in the north of the estuary but this is outside the zone of interest of this project.

The Columbia River Estuary is one of the National Estuary Programs (NEP).

Research team: Phil Ashworth, Jim Best, Rory Dalman, Andrew Nicholas, Daniel Parsons, Eric Proocki, Greg Sambrook Smith, Steven Sandbach, Chris Simpson.

Partners

This project benefited from the expertise, guidance and spirit of cooperation shown to us from the following persons and organisations. Without their considerable help this project would not be possible. Any shortcomings of this project remain our sole responsibility and not those of the organisations and individuals listed below.

The Center for Coastal Margin Observation & Prediction (CMOP), Antonio Bapitista and the CMOP team, Clatsop Community College, Stephen Schoonmaker, Kristen Wilkin, JoAnn Zahn, Deltares, Bert Jagers, ExxonMobil, Howard Feldman, Patricia Montoya,  The Marine and Environmental Research and Training Station (MERTS), Katie Rathmel, Michael Wilkin, US Army Corps of Engineers, Jacob Macdonald, Michael Ott, Lower Columbia River Estuary Partnership, Keith Marcoe, USGS Water Science Center (Illinois), USGS Water Science Center (Portland), Greg Fuhrer, Jim O'Connor, Ryan Jackson, Kevin Johnson, Douglas Yeskis, Pat Killion - Tansy Point boat driver and local expert on the ever-changing conditions in the Columbia River Estuary.

Conference abstracts

Keevil, C.E., Parsons, D.R., Ashworth, P.J., Best, J.L., Sandbach, S.D., Sambrook Smith, G.H., Prokocki, E.W., Nicholas, A.P. and Simpson, C.J. (2013) Flow structure and bedform dynamics around tidally-influenced bars. Presented at: Marine and River Dune Dynamics, 15 & 16 April 2013, Bruges, Belgium.

Ashworth, P.J., Best, J.L., Nicholas, A., Parsons, D.R., Prokocki, E., Sambrook Smith, G. and Simpson, C. (2012) Bar morphodynamics in the fluvial-tidal zone. Presented at: American Geophysical Union Fall Meeting 2012, 3 December - 7 December 2012, San Francisco, USA.

Ashworth, P.J., Sambrook Smith, G.H., Best, J.L., Nicholas, A.P., Parsons, D.R., Prokocki, E., Sandbach, S.D. and Simpson, C.J. (2012) Sedimentology of tidally-influenced fluvial deposits. Presented at: From Catchment to Coast: Fluxes and transformations through the river-estuary system, 8 January - 10 January 2012, Bangor University, North Wales.

Best, J.L., Ashworth, P.J., Nicholas, A., Parsons, D.R., Prokocki, E., Sambrook Smith, G., Simpson, C. and Sandbach, S.D. (2012) Bedform morphology across the fluvio-tidal transition, Columbia River, USA. Presented at: American Geophysical Union Fall Meeting 2012,
3 December - 7 December 2012, San Francisco, USA.

Sandbach, S.D, Ashworth, P.J., Best, J.L, Nicholas, A.P., Parsons, D.R., Sambrook Smith, G.H. and Simpson, C. (2012) Hydrodynamics of the tidally-influenced fluvial zone, Columbia River Estuary, USA. Presented at: From Catchment to Coast: Fluxes and transformations through the river-estuary system, 8 January - 10 January 2012, Bangor University, North Wales.

Sandbach, S.D., Nicholas, A., Ashworth, P.J., Best, J.L., Parsons, D.R., Sambrook Smith, G., Simpson, C. and Keevil, C. (2012) Modelling depth-averaged flow in the fluvial-tidal zone: the spatio-temporal interaction of river discharge and tidal cycle. Presented at: American Geophysical Union Fall Meeting 2012, 3 December - 7 December 2012, San Francisco, USA.

Sandbach, S.D., Ashworth, P.J., Best, J.L., Nicholas, A.P., Parsons, D.R., Sambrook Smith, G.H. and Simpson, C.J. (2011) Hydrodynamics of the tidally-influenced fluvial zone, Columbia River Estuary, USA. Presented at: The International Delft3D Users Meeting 2011, 31 October and 1 November 2011, Delft, The Netherlands.