Development of the design rainfall is a fundamental aspect to a hydrological study and alternative block method is an accepted method to derive a design rainfall from a given IDF equations.
The alternating block method (Chow, Maidment, Mays, 1988). This is the simplest way of arranging a design rainfall when you do not have a critical pattern. Otherwise, you have to do a pattern analysis and derive your own pattern specific to that particular catchment area
