Selective Depression Filling for Terrain-Derived Surface-Water Connectivity States: An Irregular-Cell Routing Framework

Surface-water networks evolve as depressions fill, spill, and connect, whereas conventional digital elevation model (DEM) routing often treats flats and depressions through preprocessing or complete filling. This study introduces selective depression filling (SDF), a terrain-based framework that generates routing states characterized by depression extent, network connectivity, and geometric fill-to-spill volume. SDF aggregates 8-connected DEM cells with identical elevations into irregular cells (ICs), preserving the lateral geometry of flats, lakes, and channels, and uses a catchment-to-destination area (C/D) ratio to control depression-filling levels. IC-D8 (IC-based single-flow-direction routing scheme) and IC-MFD (IC-based multiple-flow-direction routing scheme) routing are evaluated across four contrasting landscapes. Both methods avoid ambiguous cellwise routing across flat and low-gradient features. Depression filling changes connectivity and contributing-area propagation as depressions transition from internal termini to widened flow-path components at spillover. Filling depths define DEM-derived topographic accommodation space rather than available water-storage capacity. Differences in C/D ratios define a Contributing-Area Sensitivity Metric (CSM), a terrain-based routing contrast rather than flood probability. Because the C/D ratio and filling states are derived from terrain data without independent hydrological forcing, the uncoupled SDF is a terrain-morphological analysis framework, not a hydrological model; hydrologic interpretation and regional transferability require independent calibration, validation, and testing across regions.