A Low-Return-Period Rainfall Intensity Formula for Estimating the Design Return Period of the Combined Interceptor Sewers

The design rainfall intensity and its return period of the combined interceptor sewer is an important factor affecting overflow (CSO) occurrence. However, we often use ratio (or multiple, n0) to sewer, equivalent ignored. In this study, a low formula modeling method was proposed estimate period. First, new event separation approach especially developed, minimum interevent time (MIET) set concentration tributary area corresponding most downstream well. Second, sampling algorithm, annual multi—event—maxima (AMEM) put forward. For several maxima should be sampled annually, only one maximum for each event. addition, empirical frequency values above intensities can obtained according mathematical expectation (Weibull formula). After comparison, lognormal distribution selected theoretical probability density function. Finally, parameters were estimated using three-parameter Horner MCMC (Markov Chain Monte Carlo) algorithm. A case study conducted demonstrate based on recorded data from meteorological station in southwestern China system. Results revealed that: (1) MIET determination independence CSO events. (2) An multi-event-maxima collecting samples intensity. (3) best-fit distribution. (4) Resulted provided.