Nouns ending in -tion are feminine.
The suffix forms abstract nouns of action or state.
Is augmentation masculine or feminine?
l'augmentation
The rule behind it
99.8% of -tion nouns are feminine
In context
La population urbaine des États-Unis est en augmentation.
The urban population of America is increasing.
J'ai réclamé une augmentation à mon patron.
I asked my boss for a pay raise.
J'ai réclamé une augmentation à ma patronne.
I asked my boss for a pay raise.