Low-gradient coastal watersheds are susceptible to flooding caused by various flows such as rainfall-runoff, astronomical tides, storm surges, and riverine flows. Compound flooding occurs when at least one coastal flood driver occurs simultaneously or in close succession with a pluvial and/or fluvial flood driver, such as during a tropical cyclone event. This study presents a one-dimensional (1-D), reduced-order physics compound inundation model tested over an idealized coastal watershed transect under various forcing conditions (e.g., storm surge, astronomical tides, and rainfall) that varied in magnitude, time, and space. This study aims to evaluate each flooding mechanism and the associated hydrodynamic responses to identify generalized coastal transition zones and enhance the production of flood maps for varying regions in a coastal watershed. Compound inundation levels are affected by the magnitude and timing of each flooding mechanism. The desire is a more holistic compound inundation model that can be a critical tool for decision-makers, stakeholders, and authorities who provide evacuation planning to save human lives and enhance resilience.