Projects

Projects:

The following grants are linked: NE/H00582X/1, NE/H006524/1, NE/H007261/1 and NE/H007954/1

The overarching aim of this project is to develop a quantitative understanding of the morphodynamics and sedimentology of the tidally-influenced fluvial zone (TIFZ). This central aim will be addressed through accomplishing the following objectives:

O1.Quantify the bed morphology of theTIFZ, identify the principal bedforms and track the development of bars through use of historical data and production of repeat high-resolution DEMs, within an 80 km² reach that covers the full TIFZ.

O2.Quantify the 3D flow field, bedload and suspended load transport rates and grain size over and around key bars identified in O1, on flood, ebb, spring/neap tides and the freshet.

O3.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 O1 and O2.

O4.Establish the typical facies type and thickness, frequency and spatial distribution of different elements of the alluvial architecture of largebars in the TIFZ.

O5.Distinguish the diagnostic structures of fluvial, fluvial-tidal and tidal-fluvial deposits across and down the TIFZ.

O6.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 O4.

All rivers across the globe that exit to the ocean contain a zone, which can be 100’s 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 mankind 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. Thus in order to better maintain, manage and protect these fragilezones, we must understand how and why these regions change and what factors control such change. Additionally, the sediments of ancient TIFZ’s 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 with ancient TIFZ sediments. Understanding the internal nature of such TIFZ sediments is thus of paramount importance when attempting to extract the maximum quantity of oil (or gas) from such ancient hydrocarbon reservoirs - we need to know what controls the geometry and internal characteristics of these reservoirs, and thus better plan efficient and maximal hydrocarbon extraction strategies.

Thus all ofthese interests in both modern and ancient TIFZ environments depend on a detailed knowledge of the fluid flows in these areas, how such flows transport their sediment and critically how the form (or morphology) of these environments changes through time. However, due to the extraordinary challenges of working in such a complex and dynamic environment, few high-resolution, spatially-representative, fielddatasets exist and remarkably little work has been undertaken on the diagnostic internal sedimentary structureof such TIFZ deposits. Additionally, whilst there has been progress on the mathematical modelling of estuarine flow and sediment transport, these models remain largely untested. There is therefore a pressing need to link the processes and deposits of the TIFZ through an integratedstudyof their flow, morphology and sediment movement to quantify the key processes and how these are represented within the subsurface sedimentary record. This proposal outlines an integrated field and mathematical modelling study that seeks to achieve a step-change in our understanding of the TIFZ, using the very latest techniques in field survey and mathematical modelling. These techniques willyield unrivalled high-resolution datasets of bathymetry, flow, sediment transport and sedimentary structure that will then be usedto 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 resultswill transform our understanding of how such TIFZ zones behave in modern environments and critically how these changes may be recognized within ancient sedimentary successions.