a separator module for a stormwater gully chamber is disclosed , the separator module comprising : a partition arrangement which , in use , divides the chamber into an upper region and a lower region , the partition arrangement comprising : an inlet chute having an opening which , in use , provides an inlet to the lower region from the upper region ; an outlet chute having an opening which , in use , provides an outlet from the lower region to the upper region ; and a weir separating the outlet chute from the inlet chute ; wherein at least a portion of the partition arrangement is flexible so as to allow an external diameter of the partition arrangement to be adjusted to fit different sized chambers .