Comparative Assessment of D8 and D∞ Algorithms for Drainage Delineation and Digital Terrain Model Resolution Effects on Environmental Sensitivity Mapping

Drainage products derived from digital terrain models (DTMs) depend on resolution, flow routing, and channel-initiation thresholds. This study compared the Deterministic Eight (D8) and D-infinity (D∞) algorithms for drainage delineation in the 26.9 km2 Ponte Grande River watershed, Lages, Brazil. Height Above the Nearest Drainage (HAND) and Topographic Wetness Index (TWI) maps were derived from D8 only. A 1 m DTM (2012 aerial survey) was aggregated to 5, 10, and 30 m and conditioned in TauDEM. Thresholds were tuned visually for each configuration against the Santa Catarina state hydrography (SIGSC); no positional-accuracy metrics or flood records were used. The 1 and 5 m DTMs produced dense, microtopography-driven networks (up to 1.99 km/km2) and fragmented HAND and TWI patterns. D∞ produced more diffuse flow, whereas D8 produced more concentrated, hierarchical networks, a criterion that favors D8 by construction. The 10 and 30 m DTMs gave the more interpretable outputs; D8 at 30 m had the lowest drainage density (0.76 km/km2), partly because of its larger threshold. Thresholds differed among configurations and were tuned against the same reference, so algorithm, resolution, and threshold effects are confounded and agreement may favor coarser DTMs. HAND and TWI are topographic proxies; linking them to flooding requires hydraulic or event data.