The Frequency Distribution Estimation Method of Excess Rainfall Intensity of Double Thresholds (ERId) for Combined Sewer Overflow

Xingpo Liu (), Liang Shen, Wenke Zang and Yuwen Zhou
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Xingpo Liu: Shanghai Maritime University
Liang Shen: Shanghai Maritime University
Wenke Zang: Shanghai Maritime University
Yuwen Zhou: Beijing University of Technology

Water Resources Management: An International Journal, Published for the European Water Resources Association (EWRA), 2024, vol. 38, issue 11, No 21, 4379-4392

Abstract: Abstract Nowadays, many cities in China are facing the challenge of returning black and odorous waters during the rainy seasons. Combined sewer overflow (CSO) was one of the critical triggers. In this study, a new method for estimating frequency distribution of the excess rainfall intensity considering double thresholds (ERId in short) was proposed, which is helpful for estimating severity of CSO. For the specific interceptor well, the upper threshold is the design areal unit discharge (the equivalent rainfall intensity) of its upstream combined sewer and the lower one is the design areal unit discharge of its downstream interceptor sewers minus dry weather flow rate. First, rainfall events were divided and the minimum inter-event time (MIET) was set based on the time of concentration of the combined sewer catchment. Second, double-threshold method was used for ERId calculation and sampling for scenario of 30- minute CSO duration. Finally, the empirical frequency of the sampled ERId(30) was calculated by the mathematical expectation formula (Weibull formula) and five functions (doubly censored exponential distribution, exponential function, Gumbel distribution, Weibull distribution and lognormal distribution) were used for comparison to obtain the best theoretical frequency distribution. Results revealed that: (1) The excess rainfall intensity of double thresholds (ERId) is suitable for characterizing CSO. (2) The frequency distribution of ERId was right (positively) skewed. (3) The kurtosis of the ERId samples is not greater than 3 for all the thresholds studied, which indicates that the distribution is thin-tailed. (4) The optimal frequency distribution function for ERId is doubly censored exponential distribution.

Keywords: Combined Sewer Overflow (CSO); Excess Rainfall Intensity of Double Thresholds (ERId); The Combined Interceptor well; Return Period; The Doubly Censored Exponential Distribution (search for similar items in EconPapers)
Date: 2024
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DOI: 10.1007/s11269-024-03870-4

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