Research papersDerived flood frequency distributions considering individual event hydrograph shapes

- Improvement of the analytical probabilistic approach, a stormwater management model.
- Mathematical equations describing frequency distribution of peak discharge rate.
- All possible approximating hydrograph shapes were considered.
- Flood frequency distributions for use in urban stormwater management studies.
- Favorable results were found as compared to the widely used design storm approach.

Derived in this paper is the frequency distribution of the peak discharge rate of a random runoff event from a small urban catchment. The derivation follows the derived probability distribution procedure and incorporates a catchment rainfall-runoff model with approximating shapes for individual runoff event hydrographs. In the past, only simple triangular runoff event hydrograph shapes were used, in this study approximating runoff event hydrograph shapes better representing all the possibilities are considered. The resulting closed-form mathematical equations are converted to the commonly required flood frequency distributions for use in urban stormwater management studies. The analytically determined peak discharge rates of different return periods for a wide range of hypothetical catchment conditions were compared to those determined from design storm modeling. The newly derived equations generated results that are closer to those from design storm modeling and provide a better alternative for use in urban stormwater management studies.