How can hydrological connectivity inform catchment scale stormwater flood management?

Area of Science:

• Environmental Hydrology
• Urban Water Management
• Geospatial Analysis

Background:

• Current stormwater management focuses on local solutions, often failing to achieve catchment-scale flood mitigation.
• The role of hydrological connectivity (HC) in organizing urban flood inundation patterns is underutilized in current planning paradigms.
• Operationalizing HC as a spatial diagnostic tool is crucial for understanding and managing urban flooding.

Purpose of the Study:

• To apply the Index of Hydrological Connectivity (IHC) for diagnosing connectivity controls on urban flooding at the catchment scale.
• To evaluate the explanatory power of multi-scale IHC features using machine learning for strategic flood planning.
• To identify key connectivity features that govern flood initiation, concentration, and propagation.

Main Methods:

• Generated flood inundation patterns using a validated 2D hydrodynamic model for various design storms (10-, 30-, 100-year).
• Employed an interpretable machine-learning method (XGBoost) to assess the relationship between IHC features and simulated flood scenarios.
• Investigated the impact of spatial aggregation of IHC features on flood pattern representation at different scales.

Main Results:

• Spatial aggregation of IHC features significantly improved the representation of flood patterns, with optimal performance at a 240m neighborhood scale.
• Identified a depth-dependent regime shift: shallow flooding is storage-limited, while hazardous depths are conveyance-limited.
• Hazardous flood depths are driven by slope-energized inflow interacting with corridor continuity and bottlenecks, with nonlinear and interaction-rich dependencies.

Conclusions:

• The Index of Hydrological Connectivity (IHC) provides a diagnostic framework for delineating flood conveyance corridors, bottlenecks, and inflow feeders.
• IHC helps prioritize interventions by identifying areas where hazardous inundation initiates, concentrates, and propagates.
• Integrating IHC enables site-scale stormwater measures to function coherently within a catchment-scale flood mitigation system.