Sedimentation resulting from road development, Cape Tribulation Area

The aims of the study were: to quantify the amount of sediment being carried by the streams of the Cape Tribulation area under both natural conditions and in disturbed areas adjacent to the New Road; to quantity the amount of sediment in the water column adjacent to the reefs; and to put into context the amount of increased sedimentation directly due to road developmen

Bedform dynamics from coupled bed-flow direct numerical simulations

We present results of time-evolving coupled direct numerical simulations between an erodible bed and an overlying pressure-driven, turbulent flow field. A total of 6 simulations are considered, the details of which are shown in Table 1. The numerical setup consists of a horizontally periodic open channel, and the simulations are run at a shear Reynolds number of Reτ = 180. The coupling between the spatially and temporally evolving sediment bed and the flow field is enforced through the explicit immersed boundary method (IBM) of Uhlmann [1]. The flow field is fully resolved and is obtained by integrating the conservation of mass and momentum equations using a pseudo spectral code [2]. On the other hand, the sediment bed is modelled via the Exner equation [3]. Details about the numerical approach are available in [4-5]

Bedform dynamics from coupled bed-flow direct numerical simulations

We present results of time-evolving coupled direct numerical simulations between an erodible bed and an overlying pressure-driven, turbulent flow field. A total of 6 simulations are considered, the details of which are shown in Table 1. The numerical setup consists of a horizontally periodic open channel, and the simulations are run at a shear Reynolds number of Reτ = 180. The coupling between the spatially and temporally evolving sediment bed and the flow field is enforced through the explicit immersed boundary method (IBM) of Uhlmann [1]. The flow field is fully resolved and is obtained by integrating the conservation of mass and momentum equations using a pseudo spectral code [2]. On the other hand, the sediment bed is modelled via the Exner equation [3]. Details about the numerical approach are available in [4-5]

Quantifiable effectiveness of experimental scaling of river- and delta morphodynamics and stratigraphy

Laboratory experiments to simulate landscapes and stratigraphy often suffer from scale effects, because reducing length- and time scales leads to different behaviour of water and sediment. Classically, scaling proceeded from dimensional analysis of the equations of motion and sediment transport, and minor concessions, such as vertical length scale distortion, led to acceptable results. In the past decade many experiments were done that seriously violated these scaling rules, but nevertheless produced significant and insightful results that resemble the real world in quantifiable ways. Here we focus on self-formed fluvial channels and channel patterns in experiments. The objectives of this paper are 1) to identify what aspects of scaling considerations are most important for experiments that simulate morphodynamics and stratigraphy of rivers and deltas, 2) to establish a design strategy for experiments based on a combination of relaxed classical scale rules, theory of bars and meanders, and small-scale experiments focussed at specific processes. We present a number of small laboratory setups and protocols that we use to rapidly quantify erosional and depositional types of forms and dynamics that develop in the landscape experiments as a function of detailed properties, such as effective material strength, and to assess potential scale effects. Most importantly, the width-to-depth ratio of channels determines the bar pattern and meandering tendency. The strength of floodplain material determines these channel dimensions, and theory predicts that laboratory rivers should have 1.5 times larger width-to-depth ratios for the same bar pattern. We show how floodplain formation can be controlled by adding silt-sized silicaflour, bentonite, Medicago sativa (alfalfa) or Partially Hydrolyzed PolyAcrylamide (a synthetic polymer) to poorly sorted sediment. The experiments demonstrate that there is a narrow range of conditions between no mobility of bed or banks, and too much mobility. The density of vegetation and the volume proportion of silt allow well-controllable channel dimensions whereas the polymer proved difficult to control. The theory, detailed methods of quantification, and experimental setups presented here show that the rivers and deltas created in the laboratory seem to behave as natural rivers when the experimental conditions adhere to the relaxed scaling rules identified herein, and that required types of fluvio-deltaic morphodynamics can be reproduced based on conditions and sediments selected on the basis of a series of small-scale experiments

Experimental distributive fluvial systems: Bridging the gap between river and rock record

A debate has called into question as to which fluvial channel patterns are most widely represented in the stratigraphic record, with some advocating that distributive fluvial systems (DFS) predominate and others that a broad diversity of fluvial styles may become preserved. Critical to both sides is the adequate recognition of original channel planform from geological outcrops separated from their formative processes by millions or even billions of years. In this study the river and rock record are linked through experimentally created DFSs with both aggrading channel beds and floodplains. This approach allows depositing processes and deposited strata to be studied in tandem. Proximal areas comprise coarse, amalgamated channel-fills with scarce fine-grained floodplain material. The overall spread of sandbody dimensions become far more varied in medial stretches, with an overall reduction in mean width and depth. In these areas channel-fills may be sand-rich or mud-rich and, following avulsion, all channels are covered by floodplain sediment. Channels, levees and splays form discrete depositional bodies each with varying aspect ratios; a novel breadth of deposits and morphologies in aggrading experiments largely concurrent with proposed trends indicative of DFSs. The proportion of floodplain material increases distally, resulting in decreased interconnectedness of distal channel-fills. Muddy floodplain sediments significantly change DFSs behaviour and subsequent stratigraphic architecture by enhancing bank stability and reducing avulsion through the filling of floodbasins. The laboratory methods utilised here open up the possibility of controlled experimentation on the effects and mechanisms of DFSs sedimentation, which is important since the modelled stratigraphic trends are rarely so tractable in ancient geological outcrop belts