Portfolio managers

Tijmen Steensma - Secretary Portfolio Managers

Biography, education and career

In 2025, Tijmen took office as Secretary Portfolio Managers. In 2023, he completed his master's degree in Complex Systems Engineering & Management at Delft University of Technology. During his studies, Tijmen worked at several startups, after which he did the State Traineeship at the Ministry of Economic Affairs and Climate. In early 2025, he made the move to TNO Vector, where he continued his career.

Ancillary activities

Tijmen Steensma is PR Commissioner of the board of YKE.

There are too few engineers in the Lower House

"For years it has been written that there are too few engineers in politics. While politicians decide on technical issues such as building nuclear power plants, bridges and dykes, policy on wind energy, nitrogen and semiconductors and subsidies for innovation. Portfolio managers can support politicians by connecting politicians with the right technical experts within KIVI. Conversely, Portfolio Managers could help KIVI members put their advice to the right people in politics."

Engineers and politicians need to come together

"Engineers and politicians often think from their own perspective. By talking to each other, they eventually find out that the truth lies somewhere in the middle. This is why we from YKE want to facilitate the conversation between engineers and politicians. Both professional groups share the same ambition to make the world a more beautiful place, so let's join forces in this above all!"

Mert Kösedag - Portfolio manager Built Environment

Biography, education and career

Mert Kösedag has been involved with YKE as Portfolio Manager: Built Environment since November 2025. He studied Water Management at the Hogeschool Rotterdam and conducted research on the future water safety challenges around the Maeslant barrier. Besides his studies, Mert worked at a consultancy firm on quay reinforcements, integral redesigns of outdoor space, and nature restoration, and collaborated on the realisation of Europe's largest hydrogen plant on the Maasvlakte. Mert is currently pursuing a master's degree in project management at Utrecht University of Applied Sciences and fulfils an advisory role for the Water Board Amstel Gooi and Vecht's Framework Directive Water programme.

Ancillary activities

Mert Kösedag does not carry out any ancillary activities.

Young engineers' voice can be strengthened by combining engineering and governance

"Society faces some major challenges. Attention is needed on issues such as a climate-proof living environment, especially in terms of subsidence and sea level rise. By using my combination of technical knowledge and administrative interest, I want to focus on getting the right message across in the right place, to effectively strengthen the voice of young engineers."

Siebe van der Burg - Portfolio manager Built Environment

Biography, education and career

Siebe van der Burg has been involved with YKE as Portfolio Manager: Built Environment since 2026. He studied Civil Engineering at Delft University of Technology and obtained his master's degree in Civil Engineering: Hydraulic and Offshore Structures in 2025 from the same university. During his studies, Siebe worked at various companies and research institutes in the civil and offshore sector. Since July 2025, he has been working as a civil engineering project engineer at an engineering firm.

Ancillary activities

Siebe van der Burg does not carry out any ancillary activities.

Engineers have a responsibility to be empowered

"Engineers tend to keep to themselves behind the scenes. They calculate, design and build, but in a world facing complex challenges such as energy transition, digitalisation and climate adaptation, technical knowledge is no longer just an executive tool. Technical knowledge should be the basis for policy, which is why it is important to give engineers a voice in this."

Arwen Matthijssen - Portfolio manager Energy & Renewables

Biography, education and career

Arwen Matthijssen started as Portfolio Manager: Energy & Renewables at YKE in 2023. In 2018, she obtained a master's degree in Complex System Engineering and Management from Delft University of Technology. After that, Arwen started working as a consultant in process management and systems technology, eventually moving into asset management. Besides her work, Arwen is a board member at KIVI Assetmanagement & Maintenance.

Ancillary activities

Arwen Matthijssen is a board member at KIVI Assetmanagement & Maintenance and NxtGen.

Everything can be made

"From my passion for travelling, my motivation also arose to maintain and continuously improve the world we have created together, to prevent future problems. Fortunately, as an engineer, I believe that everything is makeable. The sun goes up for nothing, which already sends us enough energy every hour, to meet the annual global energy needs. Just imagine what our generation can achieve, if we pool our innovation power, to discover how to harvest and harness this energy optimally for all our assets."

Joining hands to strengthen each other

"At a time of enormous challenges, such as the tightening labour market due to an ageing population and the huge replacement task of civil engineering works, the young engineer hardly has time to develop himself. Right now, we are short of hands across the sector, so let's join hands and strengthen each other. By expanding and sharing my knowledge in the field of sustainable technology within KIVI, I want to contribute to energy transition, life-extending maintenance, circular and emission-free working and climate adaptation for future-proof asset management."

Marleen van de Kerkhof - Portfolio manager Mobility, Transportation & Logistics

Biography, education and career

Marleen van de Kerkhof joined YKE as Portfolio Manager: Mobility, Transportation & Logistics in 2026. She studied Technical Public Administration at Delft University of Technology, where she specialised in the interaction between technology, policy and political decision-making. During her studies, she was involved in the early development of the hyperloop and did an internship in the Dutch Parliament.

In her professional career, Marleen has delved further into improving railway safety and capacity. In doing so, she works daily at the interface of innovation and policy, with a strong focus on international cooperation and translating technical developments into applicable policy information.

Additional work

Marleen is a supervisor at 013 Poppodium and the Young Climate Movement. She is also a board member at Rail Cargo Information Netherlands and ambassador for diversity in transport at the European Commission. She also fulfils the role of Chairman of the International Rail Transport Knowledge Circle at Railforum.

Technological developments require administrative interpretation

"We are facing urgent social issues in areas such as energy supply, climate adaptation, digitalisation, spatial planning and the resilience of vital infrastructure. These issues touch upon complex technological systems and long-term choices. Understanding technological developments is essential. Wise decisions arise when the human-oriented view of the alpha and gamma sciences is linked to the analytical and system-oriented view of the beta sciences. That connection is not yet sufficiently structurally embedded in politics."

KIVI as a bridge between engineering and politics

"For years it has been observed that technical expertise is underrepresented in the political domain. Until there are more betas in the Lower House, KIVI fulfils an important role by making that knowledge available and positioning it where it is needed. My background in Technical Public Administration enables me to support building the bridge between technology, policy and society.

As Portfolio Manager Mobility, Transportation & Logistics, I am committed to effectively linking technical expertise to policy choices that contribute to a safe, sustainable and future-proof mobility system."