Modeling the cumulative impact of minor impoundments on watershed hydrology: Enhancements to the Xin’anjiang model

Abstract

Research on the mechanistic influence of minor impoundments on runoff generation and watershed convergence, along with improved simulation methods, is crucial for enhancing flood forecasting precision. This study classifies minor impoundments into three types—single-reservoir, cascaded, and parallel—and models their cumulative impact on a watershed. A novel multi-bottom sills graded weir flow pattern (MBSP) is introduced, leading to a new storage-and-discharge equation, which is integrated into the Xin’anjiang (XAJ) model to create the modified Xin’anjiang (CM-XAJ) model. The CM-XAJ model was evaluated using data from 13 flood events, showing significant performance improvements: Mean Nash-Sutcliffe efficiency coefficient (MNS) increased by 0.27 and 0.40 during calibration and validation, peak time error (M_Etp) reduced by 0.9 and 0.7 h, and flood volume (Q_v) and peak pass rates (Q_p) improved by 30 % and 66.7 %. The CM-XAJ model performs particularly well at the start of the flood season or after prolonged dry spells but is less effective during later stages or for multi-peak events. While the model shows promise, its performance decreases for larger floods, suggesting opportunities for future refinement.

The code will be available from the corresponding author upon reasonable request.