What are the functions of wetwells?

Wetwells are designed to store temporarily water/sewage before it is pumped out. They are usually provided for sewage and stormwater pumping stations and they serve the following functions:

(i) They assist in attenuating the fluctuations of flow owing to the diurnal variation of sewage discharge.

(ii) The wetwells serve as sump pits where the suction pipes are inserted and the fluid level in the sumps can be employed for the control of opening and closure of pumps.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.