In the dry periods the sanitary sewer network carries the waste water, and in the wet periods the network carries the waste water and the drainage water. For that reason, it is necessary to take into consideration the transient drainage processes when deciding on the dimensions of water storage reservoirs. Rainwater retention basins are control elements of the sanitary sewer network and storm drains, which allow to limit the flow generated in the storm periods and to delay the drainage process by intermediate storage. Dams are used to store water, to supply water in periods of drought, to obtain energy and as a protection against floods. The drainage processes in storage reservoirs is carried out by tunnels, pipelines, fittings, etc. The surge chamber prevents water hammers in pipelines and fittings in the event of rapid changes in flow rate. The Computer Controlled Unit for Transient Drainage Processes in Storage Reservoirs (PDDRC), allows to simulate transient drainage processes between storage reservoirs and the operation of a surge chamber.