Marissa Treacher’s Three Waters Journey

From Global Experience to Local Impact: Marissa Treacher’s Three Waters Journey 

Marissa Treacher brings a truly global perspective to her role as a Principal Three Waters Engineer at Harrison Grierson. From early work in New Zealand to major infrastructure projects in the UK and the United States, her career has been shaped by curiosity, adaptability, and a drive to understand complex systems. 

After studying civil engineering at the University of Auckland, Marissa began her career specialising in hydraulic modelling for stormwater. She later expanded her expertise overseas, working in the UK on drinking water network modelling and contributing to the iconic Thames Tideway Tunnel project — a large-scale wastewater system designed to improve the health of the River Thames. 

Her work then took her to Los Angeles, where she spent five years supporting city-scale water and wastewater planning, further strengthening her expertise in distribution modelling and large urban systems. 

Returning to New Zealand in 2021, Marissa joined Harrison Grierson, where she now focuses on stormwater and advisory services, including work with Auckland Council. 

Making a Difference When It Matters Most 

One of the most impactful aspects of Marissa’s recent work has been supporting Auckland’s recovery following the devastating anniversary flooding and Cyclone Gabrielle. 

Working directly with affected communities and alongside Council teams, she contributed to understanding the causes and impacts of these events — helping shape the response and future resilience planning. 

“This experience pushed me out of my comfort zone,” she reflects, describing the importance of engaging with people who had lived through the flooding. 

The scale of the events has also influenced how extreme weather is understood and planned for, prompting a rethink of what constitutes a “1-in-100-year” storm. 

“You can’t provide a good service unless you understand the real problem.” 

A Collaborative, Client-Focused Approach 

For Marissa, delivering value to clients starts with a simple principle: understanding the problem first. 

“An important part of what we do is getting to know our clients and understanding what their real drivers are. Without that, you can’t provide a good service.” 

At Harrison Grierson, she sees this approach embedded in the culture — with a strong emphasis on communication, collaboration, and taking the time to build meaningful relationships. 

“It’s a supportive environment with flexible working and great people — that really stands out,” she adds. 

Finding Your Path in Engineering 

Marissa didn’t set out with a fixed plan, but discovered her passion through experience. After exploring different areas early in her career, she found her niche in water modelling — drawn to the way it visualises real-world physical systems. 

Her advice to those entering the profession: 
Don’t stay in your comfort zone. 

“Try different things and expand your knowledge. That’s how you find what really fits.” 

Looking Ahead 

Today, Marissa is enjoying the opportunity to work closely with clients in an advisory capacity — building strong relationships and contributing to better decision-making around infrastructure and investment. 

“It’s a real partnership — you’re not working in isolation. You feel like part of the client’s team, and that’s what makes the work meaningful. 

“It’s not just technical — it’s about people, relationships, and impact.”

Connect with Marissa to learn more about drones and what they can do for your next project.