This study objective is to evaluate Gumbel's law exclusive use relative error of the in favor of theoretical and practical laws in extreme rainfall quantile estimation. To do this, an extreme rainfall database from 1941 to 2000 from the Bianouan, Agnibilékro, Adiaké and Ayamé rainfall stations on the Bia River watershed was established. The results analyzes show that the Fréchet and normal Log 2 laws are respectively the ideal laws of the theoretical and practical approach. In addition, a Gumbel's law exclusive use underestimates extreme rainfall quantiles compared to two approaches. Thus, Gumbel's law use could be justified by an economic or operational issue insofar as it understates the structures while minimizing the cost.