Field survey of post-flood damage in Denpasar, Indonesia following the September 2025 flood

Abstract

Flooding is among the most frequent and damaging natural hazards worldwide, causing substantial losses to buildings. This study presents a post-disaster field survey of the September 2025 flood in Denpasar, Indonesia. Surveys were conducted from 15 to 17 September 2025 across Denpasar, Badung, Tabanan, and Gianyar. Fifty observation points were initially collected, of which 38 were selected for analysis using a minimum spacing of 90 m to ensure spatial independence. Recorded flood depths ranged from 0 to 4 m, revealing considerable spatial variability. The surveyed area was dominated by residential buildings (46%) and single-storey structures (72%), representing a predominantly low-rise environment. Unreinforced masonry was the most common construction type (44%), followed by confined masonry (26%) and reinforced concrete (18%). Damage assessments indicated that 54% of cases involved non-structural damage and 46% structural damage. Structural damage was observed across a wider flood depth range (0–3.5 m, excluding outliers) than non-structural damage (0.4–2 m). Non-structural damage primarily affected walls, finishes, and contents, whereas structural damage included wall collapse, foundation settlement, and complete building failure. Additional impacts included severe losses to household contents and failures of retaining walls, bridges, and roads. These findings provide valuable empirical evidence for improving flood risk assessment, mitigation, and disaster preparedness.