PhD in Numerical Modelling of Short and Long-term Erosion of Permafrost Coastal Bluffs
Arctic permafrost constitutes one-third of the world’s coastline. Despite this sizeable proportion, a comprehensive understanding of erosion dynamics in the Arctic has not yet emerged. People and infrastructure are commonly located near the coast. The impact of the Arctic coastal erosion problem is widespread. Homes are being lost, population have to move away from coasts and their villages relocated. Shoreline fuel storage and delivery systems are at greater risk. Unfortunately, the majority of present knowledge regarding coastal landscape evolution is concerned to areas with temperate climates and non-cohesive sediments. Oceanographic and geomorphic feedbacks in the Arctic may be complex, but the need to interrogate these processes with physics-based modelling is becoming increasingly important. Some of the previous works indicate that Arctic coastlines have seen unprecedented increase in erosion rates over the years.
There are two main processes for Arctic coastal erosion, i.e. Thermodenudation and Thermoabrasion. The earlier is defined as the gradually thawing of permafrost bluffs due to solar radiation, warmer air temperature and snowmelt. The thawed sediment gets unstable and fails, depositing scree at the base of the slope. This scree is then eroded and finally removed through waves and currents. Thermodenudation takes place at coastlines with fine sediment with high ice content and it is characterized by low and consistent erosion rates and occurs mostly during calm conditions. Thermodenudation is more a thermal dominated process, since the sea water has no or only little contact with the frozen bluff and is just responsible for the removal of the deposited material at its toe. However, the deposited material can protect the bluff and slow down its erosion, when there are higher water levels or waves. Thermoabrasion, on the other hand, occurs during storms and high water levels, where deposited material at the toe of the slope is removed and the frozen bluff is directly exposed to the influence of the warm seawater. It then thaws quickly due to convective heat transport, whereby the melted sediment is transported off shore and out of the littoral system by waves and currents. This thawing process can lead to the formation of horizontal niches, of which the depth increases during several storms and years. When the so overhanging material becomes too heavy and cannot be hold by the shear or bending strength of the soil it collapses as a block. The block, consisting of frozen and unfrozen sediment, is then exposed to wave forces and the influence of the warm seawater and is gradually removed. Thermoabrasion is highly episodic and leads to very high and sudden coastal losses. It is highly influenced by storm surge, because then a big amount of the bluff is exposed to the seawater. Additionally, the warm seawater also erodes the coastal seabed, increasing the water depth in front of the bluff. This on the other hand makes the coastal area more accessible for longer and higher waves, accelerating the erosion process. Thus, the temperature gradient between seawater and sediment is important for the erosion rate.
Rapid changes in the Arctic coastline is due to oceanographic and geomorphic perturbations associated with climate change. Due to the changes sea ice extent is declining, sea level is rising, water temperature in the sea is increasing, and permafrost state is changing. The polar orientation of the Arctic exacerbates the magnitude and rate of the environmental forcing that facilitate coastal land area loss. The non-linear combination of these processes poses an extreme hazard. Tools to predict the Arctic coastal erosion accurately do not exist. To obtain an accurate predictive model, there is a need to couple the influences of evolving wave dynamics, hydrodynamics, thermodynamics, and sediment dynamics. One of the advantages in coupling the processes is that many of the models that can model these processes exists individually. However coupling these models presents a challenge since they involve different spatial and time scales. For an effective integrated model, models that exists individually need to have a feedback mechanism among them.
This PhD study will investigate the different physical processes associated with erosion of permafrost coastal bluffs in the Arctic. The objective is to develop a novel numerical physics-based model to predict the short- and long-term erosion rates of the bluffs. This objective will be achieved by:
- Literature review: Study of processes involved in permafrost bluffs erosion
- Propose improved formulations to describe the involved processes, e.g. submarine erosion rate (niche growth model), sediment transport model, etc.
- Implement a numerical model to assess storm impact on permafrost coastal bluffs. This includes modules for wave propagation, long waves and mean flow, sediment transport, thermodynamics, frozen soil behaviour and morphological changes. The work should utilise the recently developed theoretical models at NTNU for frozen soil (THM* models) and it should build on open-source numerical models for coastal hydrodynamics and sediment transport, e.g., XBeach**.
- Propose a methodology to assess the long-term erosion of permafrost bluffs considering both thermodenudation and thermoabrasion processes.
The candidate should have a good background in marine civil engineering, applied mathematics, physics, hydrodynamics, or mechanics, with good programming skills, good analytical skills, and the ability to work both independently and as part of a strong team. Good communication skills in English, both spoken and written are required. Arctic offshore related knowledge and experience are helpful. The candidate is expected to be self-motivated and to publish the project results in international peer-reviewed journals.
PhD Candidates are remunerated in code 1017, and are normally remunerated at gross NOK 436 900 before tax. There will be a 2 % deduction to the Norwegian Public Service Pension Fund from gross wage.
Engagement as a PhD Candidate is done in accordance with “Regulation concerning terms and conditions of employment for the posts of post-doctoral research fellow, research fellow, research assistant and resident”, given by the Ministry of Education and Research of 19.07.2010. The goal of the positions is to obtain a PhD degree. Applicants will engage in an organized PhD training program, and appointment requires approval of the applicants plan for a PhD study within three months from the date of commencement.
The position is of 3 years duration.
For further information about the position, please contact associate professor Raed Lubbad (firstname.lastname@example.org).
*THM: Thermo-Hydro-Mechanical models
**XBeach (https://oss.deltares.nl/web/xbeach/) is a two-dimensional model for wave propagation, long waves and mean flow, sediment transport and morphological changes of the nearshore area, beaches, dunes and back barrier during storms.
See https://www.ntnu.edu/iv/doctoral-programme for more information.
The engagement is to be made in accordance with the regulations in force concerning State Employees and Civil Servants. The positions adhere to the Norwegian Government's policy of balanced ethnicity, age and gender. Women are encouraged to apply.
The application must contain information of educational background and work experience. Certified copies of transcripts and reference letters should be enclosed. Applications with CV, grade transcripts and other enclosures should be submitted via this webpage at www.jobbnorge.no.
Mark the application with IV-158/18.
Start-up date may be discussed, but tentatively August 2018.
Application deadline is 20.05.2018
According to the new Freedom of Information Act, information concerning the applicant may be made public even if the applicant has requested not to be included in the list of applicants.
About this job
- Deadline Sunday, May 20, 2018
- Employer NTNU - Norwegian University of Science and Technology
- Municipality Trondheim
- Place of service Department of Civil and Environmental Engineering
- Jobbnorge ID 151379
- Internal ID 2018/11578
- Scope Fulltime
- Duration Temporary
- Applications on this job are registered in an electronic form on jobbnorge.no
- You must complete: Academic CV
- Please refer to where you first saw this job advertised!