GeoEnthalpy-Delta v1.0: an enthalpy-based model for coupled subaerial and subaqueous delta evolution with diagnostic moving boundaries

Abstract. Deltaic systems are vulnerable landscapes and stratigraphic archives, but modeling their evolution over long timescales requires methods that conserve sediment while allowing geomorphic boundaries to move. We present GeoEnthalpy-Delta v1.0, a fixed-grid enthalpy model for idealized fluvial-deltaic evolution in one and two spatial dimensions. The model evolves sediment thickness over a prescribed non-erodible basement, reconstructs the sediment surface, and diagnoses the alluvial–bedrock transition, shoreline, and delta toe from the evolving thickness and surface-elevation fields. Sediment redistribution is represented by a thresholded, slope-driven transport law with separate topset, foreset, down-system, and lateral mobility parameters, allowing finite foreset storage and fan-delta planform spreading without remeshing or explicit front tracking. We verify the one-dimensional implementation against analytical benchmarks for fixed sea level, square-root sea-level histories, vertical-foreset and graded-river limits, and post-autobreak retreat under constant sea-level rise. Two-dimensional experiments are evaluated using mass conservation, grid consistency, and moving-boundary diagnostics. Model demonstrations show that shoreline retreat can occur while the toe continues to prograde during cyclic sea-level forcing, and that lateral thresholds, foreset thresholds, sediment input, and feeder width control fan width, shoreline-to-toe separation, and sediment partitioning. GeoEnthalpy-Delta v1.0 provides a compact and reproducible baseline for studying coupled delta morphology and stratigraphy and for future incorporation of hydrodynamic, coastal, and subsidence processes.