Port locations are often selected to optimize access to land and navigable water. Many ports are therefore situated at the mouth of an estuary or along a coastline. Besides being economically important these locations are also often valuable from a biodiversity point of view. Human interventions along the coast such as port development often do not agree with local environmental processes. These interventions may be a threat to the existence of ecosystems on which our society depends in many ways. Therefore, there is an urging need for port development which is in harmony with nature and that contributes to the functioning of ecosystem services. Sustainable port development is widely regarded as ‘the answer’. This study focusses on two opportunities that can contribute to the sustainability of a port: enhancing biodiversity and the circular economy within a port and its surroundings. Generally, higher biodiversity ensures increased functioning of an ecosystem and thus supports the services an ecosystem provides. Without these services life could not exist. Enhancing the circular economy can help in mitigating the environmental pressure of a port by producing less waste and using less raw material. A promising measure to enhance both biodiversity and the circular economy at the same time within a port is constructing nature friendly banks made of residual material. Since this is not common practice in ports, it is a relatively unknown topic. The aim of this research is, therefore, to broaden the knowledge base of constructing nature friendly banks made of residual material in a port. Therefore, insight must be gained into: stakeholders and their interests in order to understand the system; critical design aspects in order to be able to identify criteria for a suitable design. Interviews with important stakeholders with different backgrounds (Rijkswaterstaat, Port of Rotterdam, Municipality of Rotterdam and WWF) are conducted to gain insight into their interests. The interviews resulted in an increased understanding and knowledge in constructing nature friendly banks made of residual material within a port. Four critical design aspects were identified during these interviews: 1. stability of the design; 2. functioning of the port and its surroundings; 3. circular economy; 4. ecological performance. Profound insight into the critical design aspects is gained by inspecting them further by obtaining a case study research and a design study. Project “De Groene Poort” in the Port of Rotterdam has been identified as a suitable case for this study. This project aims at establishing nature friendly banks in the Nieuwe Waterweg by using residual material from the port and its surroundings. The Nieuwe Waterweg is unique because of the open connection between the river and the sea, making it an important area for migratory fish. A design concept of a nature friendly bank of project “De Groene Poort” has already been developed. The main elements of this concept are a dam parallel to the bank and a nourishment between the dam and the existing bank. The dam is made of coarse residual material and aims to create sheltered conditions at the shore. The gently sloping nourishment is made of dredged material and creates intertidal area that allows more room for nature compared to the existing, steep banks. The stability is the first critical design aspect. It applies to the dam, nourishment and subsoil of the design. The port area is a dynamic environment; the governing loads are ship-induced water movements and a semi-diurnal tide. The design of the nature friendly bank has to withstand these loads and integrate with the surrounding functions of the port; the second critical design aspect. The requirements with respect to the functioning of the port and its surroundings apply to the functions: shipping, flood safety and nature and recreation. The design of project “De Groene Poort” must not impose limitations on these functions. In order to define requirements for the third and fourth critical design aspects in-depth research is required as limited information and knowledge is available on ecology in a port and the circular economy in general. One of the main objectives of project “De Groene Poort” is to enhance the circular economy of the port and its surroundings; the third critical design aspect. The project can enhance the circular economy by acting as a valuable destination for residual material and thereby reducing waste flows and the use of raw materials in the port. Project “De Groene Poort” aims to use two types of residual material as a construction material: 1. coarse residual material (e.g. debris) as a construction material for the dam; 2. dredged material as a construction material for the nourishment. Besides enhancing the circular economy, using residual material can also benefit the business case of the project by reducing expenses on dumping fees and the purchase of construction material. However, there is a high uncertainty in the availability of coarse residual material. Therefore, the final design must be flexible and adaptive to uncertainties on the fluctuating and underdeveloped market of coarse residual material. With respect to dredged material it is expected that the project imposes a small demand relative to the supply. Therefore, it is not a limiting factor for the design. Another main objective of project “De Groene Poort” is increasing biodiversity in the port and its surroundings by enhancing the living conditions of migratory fish in the area; the fourth critical design aspect. The Port of Rotterdam is situated in an estuary; an important stepping stone for migratory fish that need time and space in this area to adapt to the changing salinity between the sea and the river. Potentially, this area could be filled with fish like salmon, sturgeon and trout. However, the existing banks in the area are designed to withstand unnatural loads that are the result of intensive shipping, leaving little space for nature to develop. The area is, therefore, lacking food sources and areas for shelter. Project “De Groene Poort” can add value to the port in terms of biodiversity by providing food sources and areas of shelter for migratory fish. In order to define requirements for the final design, habitat requirements of the following groups of indicator species are, therefore, studied: 1. migratory fish; 2. food sources for migratory fish; crustacean/molluscs/polychaetes; 3. shelter for migratory fish; riparian vegetation. By improving the habitat of these indicator species, the project is expected to improve the overall ecological state of the port. The design requirements with respect to ecology affect the following factors: 1. water movement; 2. substrate; 3. salinity. Based on the requirements with respect to the critical design aspects, five alternative designs based on the existing design concept have been developed and evaluated in this study. These include a zero state model, three alternatives with dams with a varying crest level and an alternative with only a nourishment along the bank of the Nieuwe Waterweg. It has been investigated if the alternatives enable the conditions suited for the desired ecological state. This has been done by simulating the performance of each alternative with respect to every critical design aspect. The optimum design seems to be a trade-off between the objectives of enhancing the circular economy and the ecological performance. The higher the dam, the better the ecological performance but at the same time the higher the uncertainty in the availability of material. In case a lot of material is available the highest possible dam is the preferred alternative. When less material is available a lower dam is also acceptable in terms of ecological performance. These alternatives are also expected to be stable and impose no limitations on the functioning of the port and its surroundings. It has been concluded that the project imposes a relatively small demand of dredged material compared to the availability. It is, therefore, expected that using dredged material as a construction material will have limited impact on the circular economy of the Port of Rotterdam. Overall, it can be concluded that the impact of using residual material as a construction material in a nature friendly bank on the circular economy depends on the dimensions and on the scale at which a nature friendly bank is constructed. This is also related to the space that is available along the river or channel at which the nature friendly bank is constructed. Furthermore, it has been concluded that a nature friendly bank can improve the overall ecological state of a port. Results in this study prove that the (hydraulic) loads on the bank can be dissipated in favor of local ecological conditions. This can be of high value in industrial areas like ports where every ecological development is a large benefit according to ecologists. Depending on their size and scale, nature friendly banks can also add value on a regional scale. A systems approach is thereby necessary, linking different projects in order to achieve benefits on a larger scale. Overall, it is concluded that a nature friendly bank made of residual material can enhance the circular economy and the biodiversity of a port. However, the execution of approaches and methods from this study are only applied to one case. Therefore, the body of evidence is limited. It is therefore recommended to further investigate the impact of nature friendly banks for example in other ports and on locations other than along a channel.