Step 1: The Mumbai Coastal Road Project is one of the biggest infrastructure projects in Maharashtra, designed to reduce traffic congestion.
Step 2: The project involves advanced coastal engineering, especially reclamation, dykes, and storm surge protection.
Step 3: The Netherlands, known for its world-class expertise in water management and coastal engineering, has been providing technological support for the project. \[ \boxed{\text{Netherlands}} \]
Each country's recognised expertise can be weighed against what the Mumbai coastal road project actually required.
Since coastal engineering expertise of this kind is most associated with the Netherlands, option 1 is the fit.
Hence, the correct answer is Netherlands.