Factors affecting the pre-filling probability of water storage tanks

Water Storage tanks have proved to be effective for runoff control in drainage systems. Standard design procedures follow an event-based approach: a single flood at a time is considered and tank is assumed completely empty at the beginning of its filling. The possibility of pre-filling from previous events is then neglected and underestimation of storage volume can occur. In this paper an analytical probabilistic approach to estimate the probability of pre-filling is presented and effects due to outflow rate and storage volume are investigated. Derived formulas are validated by their application to a case study.