Meet the modellers
Two decades working with New Zealand waters
Submergent was established in 2023, when a long-standing team of senior modellers forged a partnership. Today, our boutique consultancy is made up entirely of technical people – engineers with significant experience in river and urban stormwater hydrological and hydraulic modelling.
Directors Carl Johnson and Rathika Jebamony now lead our small team to deliver wide-ranging hydraulic modelling projects, including scoping and schematisation, model development, technical investigations, advice, strategies, peer review and guideline development.
Carl Johnson
Director, Principal Engineer / Modeller
Carl Johnson is a specialist in hydraulic and hydrological modelling with more than nineteen years of experience across New Zealand, Denmark, Australia and Singapore. His expertise spans the full spectrum of flood and water system modelling, from large-scale 1D/2D coupled floodplain models to sophisticated Computational Fluid Dynamics (CFD) studies of individual structures.
Carl’s uncompromising approach to technical precision and output quality means he’s recognised by peers as one of New Zealand’s top specialists. His models balance technical sophistication with practicality, identifying fit-for-purpose solutions without over-engineering.
A natural educator and collaborator, he is valued for his approachability and ability to explain complex science clearly. He continues to challenge conventional modelling practices, pushing for results that are accurate, meaningful and enduring for the people who build, use, and maintain these models.
Education
Bachelor’s degree in engineering (Engineering Science)
Key projects
· Trusted advisor to Waikato Regional Council
· Northern Wairoa catchment modelling (4,000 km²) for Northland Regional Council
· Key contributor to the National Stormwater Modelling Guide (Department of Internal Affairs/Water NZ, 2024)
· Key contributor to Bay of Plenty’s Hydraulic Modelling Guidelines (2021, Draft)
· Key contributor to Tauranga City Council’s Guidelines for Stormwater Modelling v008 (2022)
· Modelling specialist for Tauranga City Council’s Stormwater Panel (2011 – 2024)
Rathika Jebamony
Director, Principal Engineer / Modeller
Rathika Jebamony has spent more than two decades as a senior water modeller and project leader across New Zealand, Australia and Canada. A recognised specialist in stormwater and wastewater modelling, she brings a broad technical perspective, adapting to diverse project contexts and leading complex projects with clarity and precision.
She is known for her strategic insight and refined understanding of the issues facing local authorities, consultants and private developers. This ensures each model and policy outcome is grounded in practicalities and delivers long-term value.
Rathika is highly regarded by industry peers for her thoroughness, consistency and leadership across multi-consultant projects. She has trained and mentored a wide range of professionals, building modelling capacity in Australasian consultancies, councils, and client organisations. Her commitment to knowledge-sharing continues throughout project delivery, empowering teams to confidently understand, adapt, and evolve their models.
Submergent’s clients and partners value her collaborative approach and the accessibility of her solutions. She works to set up structures and processes so clients can confidently manage and adapt their models over time.
Education
· Bachelor’s degree in engineering (Engineering Science)
Key projects
· Peer review of flood control scheme models for Hawke’s Bay Regional Council
· Key contributor to the National Stormwater Modelling Guide (Department of Internal Affairs/Water NZ, 2024)
· Modelling lead for Kaipara District Council’s 3 Waters panel (2020 – 2024)
· Modelling specialist for Tauranga City Council’s Stormwater Panel (2020 – 2024)
· Key contributor to Tauranga City Council’s Guidelines for Stormwater Modelling v008 (2022)
· Modelling specialist for Tauranga City Council’s wastewater systems (2017-2020)
Eric Feng
Junior Modeller
A recent graduate, Eric is already adding value to the Submergent team with his deep thinking and approach to problem-solving. While studying, he built technical skills in fluid mechanics and numerical modelling, having achieved firsts in course awards. His final-year project was to produce a large-scale flood inundation map of the Massey catchment during the Auckland Anniversary Flood (2023) – the ideal experience to bring to Submergent.
During his studies, he also worked at the university as a teaching assistant in engineering mechanics, and a research assistant looking into a hybrid CFD/ML approach to fluidic permeability prediction in bone tissue engineering applications.
Education
· Bachelor’s degree in engineering (honours), (Engineering Science)
Key projects
· Rainfall-runoff modelling for the Massey Pony Club during the Auckland Anniversary flood (2025, final-year project)
· A Hybrid CFD–Machine Learning Framework for Efficient Permeability Prediction in 3D-Printed Bone Scaffold Design (2026)
Claire Barker
Business Operations
Claire Barker is a cofounder of Submergent, playing a key role in guiding the strategic direction of the business.
She draws on her background in education and the humanities to bring strong communication, organisation and people management skills to the team. Claire has worked internationally and in a wide variety of schools and community groups, experience that has shaped her collaborative approach and ability to work across diverse teams and contexts. Her role is broad, spanning finance, HR, business management, marketing and communications, as well as coordinating events and partnerships. Much of this work happens behind the scenes, but it plays a central role in enabling the technical work Submergent is known for. Her clarity of thought and big picture perspective makes her a valuable sounding board on complex projects and client challenges.
Education
- Bachelor’s degree in arts
- Postgrad diploma in teaching (secondary)