Piscina and Castella

On basins and control mechanisms in Roman aqueducts, Part 2

Illustrations to Appendices II: Settling versus Storage basins

Settling basin	Storage basin
A. Supply almos equal to discharge
Major elements: In the flow (Almost) permanent in use (except during maintenance) one inlet (I), one exit (E) Overflow (O) is optional Drain (D) is necessary (although there are other ways of cleaning) for discharge of debris and imputities Acces for control and cleaning By-pass os optional )*	Major elements: Near the flow In use on demand Control mechanisms at inlet (O) and exit (E) to control the supply and the discharge Overflow (O) necessary for security reasons Drain (D) and access recommended (also in storage basins there is sedimentation) Loss of head (for a medium size reservoir (10 x 5 x 3) almost 3 meters !!
B. Supply < discharge
C. Supply > discharge
An overflow or by-pass mechanism has to do its work	The overflow mechanism will do its work
)* For a settling basin a by-pass mechanism is optional; for a storage basin a by-pass is problematic because of the gradient / loss of head