Dry weather flow

Dry weather flow refers to the wastewater flow in a sewer system during periods of dry weather with minimum infiltration.

The consequences of the lower flow apply to both combined sewer systems and to separate sanitary sewer systems.

Insufficient flow velocities during dry weather flow can increase retention time if pipes and channels are not designed correctly. This would result in undesirable sedimentation of solid particles and undesirable biological and chemical reactions.

Figure showing dry and wet weather flow in a combined sewer system.