Secondary circulation in partially vegetated channels

The goals of this project are to:

• Characterise the three-dimensional flow in submerged partially vegetated channels.
• Investigate the effects of vegetation density and water surface level relative to vegetation height on the flow structure of patchy vegetation.
• Model spanwise depth-averaged velocity distributions in submerged partially vegetated channels.

The details

Vegetation along river margins and banks act as porous obstructions for the flow, generating a differential velocity between the slow moving fluid inside the vegetation and the faster moving fluid outside the vegetation. This, in turn, creates strong vortical motions spiraling in the main direction of the flow. These vortical structures are also known as secondary circulation.

While the faster flowing water in the main channel carries sediment and nutrient loads, within the vegetation lies the ecological diversity and capacity for hydrological storage and sediment retention. Thus, secondary circulation can promote the exchange and retention of various types of matter between a patch of vegetation and the overlying water such as, particulates, sediments and heavy metals. This exchange is a fundamental process in a healthy aquatic ecosystem. However, vegetation can also promote local erosion and sedimentation processes, leading to rising water levels, increasing flood risk.

Therefore, this research aims to characterise the flow through patchy vegetation, and specifically the secondary circulation, to improve the system-level understanding of vegetated environments.This will translate into more robust modelling to study biological processes, such as vertical scalar transport and residence times of biological species in aquatic vegetation, as well as river modelling to assist river managers in the assessment of flood risk, enabling more informed decision making.

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Graduate researcher profile: Stefania Unigarro Villota

What did you do before you started your PhD?

I undertook this joint PhD programme to conduct research in the field environmental fluid mechanics after completing with distinction my Master’s degree in Civil Engineering for Risk Mitigation at Politecnico di Milano, Italy. During my Master’s studies, I focused on hydrogeological risk and river hydraulics, and experimentally investigated the impact of sediment fronts and bed-forms caused by sediment overloading on water levels, and consequently flood risk.

Previously, I worked for a consultancy company in various water engineering projects in Colombia (my native country), where I developed my interest in flood risk. I have a Bachelor’s degree in Civil Engineering with emphasis in structures from Pontificia Universidad Javeriana, Colombia. I graduated in the top five of my cohort, receiving distinction for the best Bachelor’s thesis in Civil Engineering. The bachelor’s thesis aimed to improve the seismic performance of the structural system of 16^th-and 17^th -century rammed-earth churches by proposing a reinforcement alternative using confinement wood elements. Subsequently, in 2019 the standards for the evaluation and intervention of heritage buildings in adobe and rammed-earth were created and incorporated into the Colombian Standards for Seismic Resistant Design and Construction. This was due to the extensive studies performed on adobe and rammed-earth structures over the previous decades.

What are the challenges of your research role?

My supervisors work in a variety of different research fields, so one of the challenges of my research is incorporating different perspectives and view-points wisely without losing focus, while also keeping everyone engaged.

On the other hand, a joint PhD has many challenges, but it is definitely rewarding! All the paperwork, the meetings, and the preparation for reviews, presentations and assessments, can seem overwhelming at times but good time-management and organisation alleviates most of the stress. Great communication is also essential. It is not always possible to have meetings with all supervisors at one time, due to the time-zone differences, and it is ultimately up to you to keep everyone updated, interested and engaged in the project. Here, it is important to be flexible as well, because meetings or activities sometimes take place before/after working hours. Although, it is not possible to explore and exploit everything each university has to offer, great benefit can be yielded from both universities.

What is the best part of your research role?

The best part of my research role is to contribute to a system-level understanding of vegetated environments in river management and coastal systems, which has become increasingly important due to climate change. To this end, the joint PhD programme provided the unique opportunity to tackle a cutting-edge project under the guidance of highly experienced and recognised researchers in two continents, and allowed meaningful discussions with peers and experts in a wide range of research fields.

Where do you wish to go after your PhD? Do you want to enter industry or continue doing more research?

Although I have very much enjoyed my PhD journey, I would like to transfer my skills and knowledge to the water engineering industry. I believe that the knowledge I have acquired can contribute positively in addressing future flood severity and its vulnerabilities to croplands, ecosystem function and societal quality of life.

Supervision team

• The University of Melbourne: Dr Jimmy Phillip
• The University of Birmingham: Dr Soroosh Sharifi