Influence of siltation on flood propagation: hydrodynamic analysis and hazard index assessment in the Jundiaí River Basin

Resumen

Siltation is one of the main aggravating factors for floods in urbanized basins, altering flow capacity and increasing socio-environmental risks. This study evaluates the impacts of siltation on flood dynamics in the Jundiaí River Basin (São Paulo, Brazil), using hydrodynamic modeling (HEC-RAS 6.0) and the Hazard Index (HI = y × v), based on hydraulic thresholds established in the literature. Three scenarios were simulated for an extreme 100-year return period (RP) event: (1) reference condition (no siltation), (2) moderate siltation (20% reduction in depth), and (3) severe siltation (40% reduction). The results indicated three distinct hydrodynamic behavior patterns: high-energy zones (where the cross-section reduction increased velocity and erosive power), active deposition zones (locations with low velocity, v < 0.3 m/s, with lateral flood expansion), and transition areas (with unstable Hazard Index behavior). An increase in the flooded area was observed by 12% (moderate scenario) and 28% (severe scenario), with a critical rise in the HI (> 4.0 m²/s) in high hydraulic energy zones, while low-velocity areas (v < 0.3 m/s) showed lateral flood expansion. Sediment deposition was predominant in floodplains and reaches with slopes < 0.3%, corroborating literature studies. It is concluded that siltation not only expands the flooded area but also intensifies hydrodynamic risks in critical regions, demanding integrated sediment management strategies.

Keywords: hazard index, hydrodynamic modeling, Jundiaí River, siltation.