The uniform design storm is the oldest and simplest design storm. The storm originates from the use of the rational method. By selecting a duration and return period, the average maximum in-tensity is found from an intensity duration frequency curve. The intensity remains constant for the duration of the storm.

The uniform design storm contains only a part of the real storm volumes. The volume of the uni-form design storm is obtained from an IDF curve it is not the volume from a real storm event. The uniform hyetograph does not show any variation in intensity with time. Real rainfall events have intensities that are highly variable, this variability affects the peak flow.