Grey and green infrastructure alternatives for water-related disaster mitigation: The case of Mandailing Natal, North Sumatera, Indonesia

Flood disaster in Mandailing Natal Regency, North Sumatera, Indonesia is challenging due to its barriers to reduce the disaster impact. Flood disaster mitigation should be prepared for both structural and non-structural alternatives to apply. Meanwhile, the government seems to face budget allocation and geographical condition of the area to choose the better alternatives. This research aims to investigate the suitable alternative to be applied in the study area as flood disaster mitigation. There are three alternatives: (1) river channel modification, (2) earth-embankment dam construction, or (3) rainwater harvesting (RWH) application. The investigation is carried out through hydrological analysis, hydraulics analysis, and numerical analysis of channel and dam by using HEC-RAS and Geo-Studio supporting tool. Meanwhile, rainwater harvesting is computed based on a mathematical model from previous studies. Since the alternative is chosen because of the runoff reduction capability and budget expenditure prediction, rainwater harvesting seems to be the more recommended to be applied in the study area. The RWH could make 86.36 runoff reduction. Despite river channel modification could extract almost 100 of runoff, the allocation for the construction is too high for the government to handle. © Published under licence by IOP Publishing Ltd.