Impact of urbanization on urban flooding: A case study of Chandragiri Municipality, Nepal

Abstract

Urban flooding has become one of the most significant hazards associated with rapid urbanization in South Asian municipalities. Chandragiri Municipality, a rapidly expanding peri-urban municipality of the Kathmandu Valley, has undergone dramatic land use transformation over the past two decades, yet the link between this urbanization and urban flooding has not been systematically studied. Hence, this study was conducted with an aim to identify the major problems of urbanization related to urban flooding in Chandragiri Municipality, their causes and effects, and appropriate mitigation measures. Primary data were collected through questionnaire survey of 156 respondents determined using Slovin’s formula, field observation in the downstream wards along the Balkhu River, in-depth interviews with seven key informants and three focus group discussions, whereas secondary data were collected from published literatures, hazard maps and municipal planning documents. The collected data were analyzed using the Relative Importance Index (RII). The results showed that major problem is insufficient storm-water drainage infrastructure in new settlements with the highest RII value of 0.92, followed by encroachment of rivers and natural waterways (RII 0.91) and loss of open spaces and pervious land (RII 0.89). Weak fines and penalties for illegal dumping (RII 0.92) and disposal of plastic, sand and construction debris into drains (RII 0.91) were the most significant causes, while water diversion towards neighboring houses and fields (RII 0.91), sudden flooding after moderate rain due to partial drain blockages (RII 0.90) and the desire to migrate out of high-risk neighbourhoods (RII 0.89) were the most significant effects. Built-up area now covers 51.4% of the municipality, and wards 15, 12, 11, 14 and 10 were the most affected, with 70, 60, 45, 25 and 8 houses experiencing recurrent inundation. Interviews and discussions revealed the absence of a drainage master plan, weak enforcement of river setbacks, non-functional early warning systems and a disproportionate flood burden on tenants, daily wage labourers, women and elderly residents. The study recommends flood-sensitive land use planning, a comprehensive storm-water drainage plan with regular maintenance, river corridor protection, sustainable drainage measures and community-based early warning systems.