A Probabilistic Model Based on Gamma Distribution for Performance Analysis of Urban Drainage Systems

Evaluating urban drainage system efficacy is critical for design and renovation. Existing probabilistic models often rely on exponential distributions, which are inadequate for specific climatic regions (coefficient of variation of rainfall characteristics does not equal 1). This study proposes a Gamma distribution-based probabilistic model, integrating B.J. Adams’ rainfall-runoff transformation theory to accurately characterize rainfall properties (volume, duration, intensity, interevent time) and assess drainage system performance. A systematic, criteria-based framework is provided to determine where the Gamma model should be preferred. The model enhances estimation accuracy by incorporating both the mean and standard deviation of meteorological data, providing a reliable tool for engineering design.