A framework for mechanism analysis and main controlling factor identification of equivalent flood-control effects in basin reservoir groups

To establish a unified mechanistic interpretation of flood-control storage equivalence in reservoir groups comprising serial, parallel, and mixed mainstem-tributary configurations, an event-scale analytical framework for equivalent flood-control effects is developed. Baseline and equivalent-cooperative operation scenarios are compared for the same flood event to define upstream additional storage, downstream volumetric flood-load reduction, and an equivalent interchange coefficient. Valid samples are screened using water-level, discharge, and actual-interchange constraints. Four dimensionless controlling factors—flood source, flood intensity, process matching, and group regulation capacity—are organized into a response matrix. The analysis shows that an equivalent flood-control effect is an event-scale system response governed by cascade routing, parallel confluence, intervening floods, and common flood-protection-section constraints. Its formation and variation can be interpreted through four mechanisms: source dominance, encounter modulation, load threshold, and topological constraint. The framework provides a theoretical basis for identifying flood-control storage interchange relationships, analyzing safety boundaries, and extracting joint flood-control operation rules.