The Rainstorm Intensity Formula For The Chief Sewage Pipeline Design In Chongqing And Its Workability Assessment Analysis

Because the sub-secondary pipeline transformation has not completed，actually,the chief sewage pipeline in Chongqing main urban area is still a combined systemalthough it was designed to be a separate system, it is the key to flood control anddrainage under the strong-intensity rainfall. Rainstorm intensity formula is the designbasis for a regional sewerage, and it should not only embody the characteristics of thelocal current extreme rainfall, but also have enough accuracy. The present rainstormintensity formula in Chongqing was derived with the insufficient material which isselected before1973, and it can’t reflect the characteristics of the current extremerainfall. Therefore, it is necessary to correct the formula and use the corrected formulato analyze the safety of the chief sewage pipeline in Chongqing main urban area.The derivation of rainstorm intensity formula relates to three key problems:(1)thesamples extraction of the rainstorm intensity;(2)the determination of the probabilitydistribution model of samples and the establishment of the localfrequency-intensity-duration table(IDF table);(3)the numerical solution for thenonlinear model parameters of rainstorm intensity formula. In this paper, according tothe requirements of codes and the recent30years’(from year1981to2010) minuteself-recording rain gauge records provided by Chongqing Weather Bureau, annualmulti-sampling method was used to extract samples, and Gumbel distribution, Weibulldistribution, Exponential distribution and Pearson-Ⅲ distribution were used to analyzethe samples. The results showed that: except for Gumbel distribution, Weibulldistribution, Exponential distribution and Pearson-Ⅲ distribution were suitable for thesamples and Exponential distribution is the best, Weibull distribution took second place,Pearson-Ⅲ distribution took third place. According to this results,frequency-intensity-duration tables(IDF tables) corresponding to the latter threeprobability distribution models were established in this paper. Then, Nanjingmethod(CRA) was used to determine each parameters of rainstorm intensity formulacorresponding to these three probability distribution models, and through the erroranalysis, the formula corresponding to Exponential distribution which had the minimumerror and can meet the requirements of codes was selected to be the new rainstormintensity formula in Chongqing. What’s more, through the comparison between new formulaand old formula, disadvantages of the old formula are pointed out. In this paper, the new rainstorm intensity formula was used to analyze thedrainage capacity and the safety of the overhead box culvert structures of the chiefsewage pipeline’s A pipeline in Chongqing main urban area after the drainage systemwas changed. The results showed that: under the strong-intensity rainfall, the structuraldamage would not appear to the overhead box culverts of A pipeline, but the combinedflow of A pipeline exceeded its design flow in some areas, and the terminal flow of Apipeline exceeded the capacity of sewage treatment plant. Therefore, overflow pipeswere needed to reduce the combined flow. According to the flow monitoring data, themeasure was effective.Finally, in order to monitor and manage the chief sewage pipeline’s A pipeline inChongqing main urban area, sewerage’s structure safety monitoring and managementsystem was established.