Coastal zones, which are characterized by coupled land-river-ocean processes, feature extensive ecological diversity and biological productivity. Climate change poses several threats to the coastal communities such as increased flooding, sea level rise, saltwater intrusion, erosion, and hypoxia. The current generation Earth System Models (ESMs) typically operate on grid cells of tens to a hundred kilometers and use simplified representations of processes at the land-ocean interface. For example, ESMs use one-way coupling of land-river-ocean processes to transport freshwater runoff from the land to the ocean through rivers. One-way coupling fails to simulate the dynamic land-ocean interface and compound flooding events due to storm surge and flood water from land and rivers. In this work, we describe new capabilities in the US Department of Energy's Energy Exascale Earth System Model (E3SM) in support of modeling coupled interactions between land, river, and ocean components. A flexible, open-source framework has been developed to generate variable resolution meshes with the ability to preserve geospatial features such as river networks and watershed for fine-scale modeling of land-river-ocean interactions. Two-way land-river and river-ocean coupling are developed to simulate changes land surface processes within floodplains and to study the impact of compound flooding in case studies of observed landfalling hurricanes in the Mid-Atlantic region. Furthermore, two-way transport of nutrients and sediments between land and river models is included. These initial model developments will prepare E3SM to simulate changes in coastal zone processes due to climate change with increased fidelity and at higher spatial resolutions.