'NERC-FAPESP' Migrating dunes over hilly terrains
Lead Research Organisation:
UNIVERSITY OF CAMBRIDGE
Department Name: Earth Sciences
Abstract
Granular materials are universal and all around us, from the devastating powers of a snow avalanche to the fabrication of medicines, and from ground coffee beans to sand castles on the beach. Despite their prevalence in our daily life, granular materials are hard to characterize and understand from a physical point of view.
Dunes are manifestations of granular materials in our natural environment. Mobile hyper-arid desert dunes threaten settlements and infrastructure of as many as one billion people worldwide. In order to protect communities and infrastructure from desertification in parts of the world that become dryer each year due to climate change, we need to understand the dynamics of the evolution of a dune, from growth of a bedform to the steady-state processes of a mature dune. Sand dune movement and mobility demands controls on influencing, altering or even stopping the marching of desert dunes. This proposal focuses on a multifaceted approach to connect the avalanching processes at the grain-level with the large-scale dune marching characteristics.
The particular type of dune under investigation is a barchan dune - a fast-moving and crescentic-shaped dune present in unidirectional wind regimes with a limited sand supply. We choose to study barchan dunes as they form a unique system: they are small, scale linearly and move fast enough to study in experiments. The progression velocity scales inversely with height and therefore individual dunes chase or run away from each other in a variety of interactions. Physical scalings and mathematical models of dune migration have made huge steps forward in recent years, but are grounded on modelling migration on an idealized flat earth, which is not a realistic scenario.
In this collaborative project, we will investigate the effect of external landscape variations and topography on the speed and the shape of these fast-moving dunes. Specifically, we are investigating three different variations: dunes on (1) an inclining/declining slope, (2) a hilly topography and (3) from a polished to a bumpy landscape. We are using two different experimental facilities: in Cambridge, we mimic 2D dunes in a periodic system over very long times, while in Campinas we are able to create true 3D dunes, evolving in fixed-time in a finite channel. This combination of experimental facilities, and effective mobility of researchers between groups, will ensure success of our set goals.
Dunes are manifestations of granular materials in our natural environment. Mobile hyper-arid desert dunes threaten settlements and infrastructure of as many as one billion people worldwide. In order to protect communities and infrastructure from desertification in parts of the world that become dryer each year due to climate change, we need to understand the dynamics of the evolution of a dune, from growth of a bedform to the steady-state processes of a mature dune. Sand dune movement and mobility demands controls on influencing, altering or even stopping the marching of desert dunes. This proposal focuses on a multifaceted approach to connect the avalanching processes at the grain-level with the large-scale dune marching characteristics.
The particular type of dune under investigation is a barchan dune - a fast-moving and crescentic-shaped dune present in unidirectional wind regimes with a limited sand supply. We choose to study barchan dunes as they form a unique system: they are small, scale linearly and move fast enough to study in experiments. The progression velocity scales inversely with height and therefore individual dunes chase or run away from each other in a variety of interactions. Physical scalings and mathematical models of dune migration have made huge steps forward in recent years, but are grounded on modelling migration on an idealized flat earth, which is not a realistic scenario.
In this collaborative project, we will investigate the effect of external landscape variations and topography on the speed and the shape of these fast-moving dunes. Specifically, we are investigating three different variations: dunes on (1) an inclining/declining slope, (2) a hilly topography and (3) from a polished to a bumpy landscape. We are using two different experimental facilities: in Cambridge, we mimic 2D dunes in a periodic system over very long times, while in Campinas we are able to create true 3D dunes, evolving in fixed-time in a finite channel. This combination of experimental facilities, and effective mobility of researchers between groups, will ensure success of our set goals.
| Description | Moved forwards understanding of the role of the basal boundary condition and the presence of topography on the evolution, shape and speed of advancement of a barchan dune. |
| Exploitation Route | Work is still ongoing to enable this through publication of the work. The data collected is also currently awaiting upload to EDIC. |
| Sectors | Environment |
| Description | Unicamp |
| Organisation | University of Colorado Boulder |
| Department | Department of Mechanical Engineering |
| Country | United States |
| Sector | Academic/University |
| PI Contribution | Complementary experiments undertaken in Cambridge and Universidade Estadual de Campinas (Brazil). The experiments in Cambridge considered dune formation and migration in a quasi-two-dimensional periodic domain and how these are affected by both the roughness of the lower boundary and the presence of macroscopic topography within the annular channel. Both teams met (and continue to meet) on a regular basis (weekly during the project, approximately every three weeks since the end of the project) to discuss on-going progress in these areas. |
| Collaborator Contribution | Complementary experiments undertaken in Cambridge and Universidade Estadual de Campinas (Brazil). The experiments in Brazil considered dune formation and migration in a three-dimensional setting at smaller scale to the experiments in Cambridge. The non-periodic nature of the experiments in Brazil means the evolution can only be monitored over much shorter time scales, while the smaller scale of the experiments means they are operating at a lower Reynolds number. As with the Cambridge experiments, both the roughness of the lower boundary and the presence of macroscopic topography within the annular channel. The collaborator at the University of Colorado, Boulder, was the original Cambridge PI on the project; the current PI took on the role when the original one relocated to Boulder. Since relocating, the original PI has remained closely involved with the project and has actively participated in the majority of meetings, bringing onboard their expertise. All three partners met (and continue to meet) on a regular basis (weekly during the project, approximately every three weeks since the end of the project) to discuss on-going progress in these areas. |
| Impact | Data set is awaiting upload onto EIDC. |
| Start Year | 2023 |
| Description | FDSE 2023 |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Postgraduate students |
| Results and Impact | Our regular Summer School on the Fluid Dynamics of Sustainability and the Environment included work on granular flows. Both the PI and PDRA associated with this project were involved in the organisation and delivery of the Summer School. |
| Year(s) Of Engagement Activity | 2023 |
| URL | http://www.fdse.org/ |