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Jurnal Pendidikan Geografi: Kajian, Teori, dan Praktek dalam Bidang Pendidikan dan Ilmu Geografi

Abstract

Flash floods are especially hazardous hydrological phenomena, noted for their abrupt occurrence and capacity to inflict severe damage on infrastructure, farmlands, and residential zones, often leading to substantial socio-economic upheaval and fatalities. A flash flood struck the Upper Brantas watershed on November 4, 2021, at 14:00, precipitated by intense rainfall over a short duration, leading to significant hydrological impacts. The event manifested at six critical points within Batu City, with Sambong Hamlet and Beru Hamlet experiencing severe inundation. The flash floods disrupted residential areas and severely affected agricultural lands through debris flows. Preliminary assessments indicated that approximately 35 houses were damaged or submerged in mud, impacting around 89 families. This study aims to analyze the storage capacity of the Upper Brantas River (Sub-watershed Brantas) and develop predictive models for future flooding events using advanced hydrological modeling techniques. Employing the Hydrological Engineering Center-River Analysis System (HEC-RAS) version 5.0.7, we evaluated river discharge dynamics and flood-inundation patterns across an approximately 33-kilometer river length. The findings reveal that rainfall fluctuations reached up to 21.86 mm during critical hours preceding the flood event, with peak river discharge estimated at 112.88 m³/s, occurring just five minutes before flooding commenced. The modeling results indicate extensive inundation covering an area of 4,402 m², underscoring significant risks associated with rapid runoff in this mountainous region characterized by steep slopes exceeding 45%. This research provides essential insights into hydrological responses under extreme weather conditions, while emphasizing land use changes as contributing factors to increased vulnerability within this sub-watershed area. This research provides a foundation for developing effective flood management strategies to mitigate future disasters in vulnerable communities along the Upper Brantas River.

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