Evaluating Design Peak Flow Estimation Methods

This study evaluates four hydrological approaches, in particular the Rational method, Fuller’s formula, EBA4SUB, and the STORAGE + COSMO4SUB (S + C) model, across five sub-basins of the Gidra River (Slovakia) for return periods (T) of 2–1000 years. In the gauged Píla sub-basin, all methods deviated from official design flows (6–44.5 m³/s), with empirical approaches showing systematic overestimation (e.g., up to 35 m³/s vs. 6 m³/s at T = 2 years), while Fuller’s formula reached up to threefold overestimation at long return periods. The S + C model provided closer agreement, generally within a factor of two. In ungauged basins, peak flows ranged from near 0 to 479 m³/s, with inter-method variability (CV at T = 1000 years) decreasing from 0.65 in small basins to 0.55 in larger ones. Empirical methods displayed largely linear scaling with basin area, which may oversimplify underlying hydrological processes. More physically-based approaches, such as S + C, offer internally consistent results, but require careful calibration and validation.