The influence of submarine outfalls on beach water quality in S?o Paulo Coast – Brazil

摘要

S?o Paulo State coast has seven sewage submarine outfalls that were builtrnwith the main objective of preventing bathing waters of fecal pollution.rnSince CETESB, the Environmental Agency of S?o Paulo State, has a longrnterm monitoring program of beach conditions assessment, it was possible tornverify the efficiency of these wastewater structures comparing beach waterrnquality in the period before with the period after their operation.rnWith this purpose the study was conducted for 20 sampling sites in 16rnbeaches located in three coastal municipalities: Santos, Guarujá and PraiarnGrande where there are four domestic waste water submarine outfalls. Therndata set corresponds to 30 years (1976 to 2005) of beach water quality inrnterms of the non-complying percent in each year, based on weeklyrnmicrobiological analysis.rnThe influence of the construction of submarine outfalls on the beach qualityrnwas then verified using SPSS for statistical analysis such as Levene test forrncomparing variances, t and Mann-Whitney tests for average comparison,rnand cluster analysis.rnFor the Santos municipality the results showed that the outfall had littlerninfluence on beach quality reducing average non-compliance index inrnapproximately 10% only, comparing the period of 1976 to 1979 with 1989rnto 1991. However, the later construction of flood gates in the drainagerncanals played an important role resulting in a significant improvement ofrnbeach quality with an average reduction of 47% of non-compliance.