| How to select a reasonable drainage system is a key problem in planning anddesign of city’s and towns’ drainage system. It not only affects design, construction andmanagement of drainage systems basically, but also has a far-reaching effect onenvironmental protection of cities and towns. At the same time, it also affectsinvestment and management cost of the projects. There are a lot of small mountainoustowns in Three Gorges Reservoir Region. They have much particularity in physicalgeography, layout and social economy. Nevertheless, most small mountainous townsmainly follow specifications or standards of big and medium cities’ drainage systemswhile drainage infrastructure is under design, construction and operation ormanagement. An unreasonable option of drainage systems leads to higher constructioninvestment and operation cost, but lower operation and management efficiency. Sovlingthe problem, runoff pollution rules in different types of small mountainous towns werefully discussed, pollutant load models of small mountainous towns for drainage systemswere constructed, and a reasonable drainage system option model for smallmountainous towns was made by spot investigation, sewage and runoff monitoring,questionnaire analysis and comprehensive evaluation. The main research results werelisted as below.①Change rule for different runoff pollutant had an inconsistency of relativity.Change rule with time for the same runoff pollutant may be different in a residentialsmall mountainous town. Change rule with time for the same runoff pollutant may besame in a small mountainous tourism town.②The frequency and intensity of first flush effect for the same runoff pollutantmay be different during different rainfalls; The frequency and intensity of first flusheffect for the different runoff pollutants may be different in the same rainfall. First flusheffect was not a common phenomenon from the current result.③SEMC of runoff pollutan TN and NH3-N in a residential small mountainoustown was higher than SEMC of TN and NH3-N i in a small mountainous tourism town,but SEMC of runoff pollutan COD, SS and TP in a small mountainous tourism townwas much higher than SEMC of COD and NH3-N in a residential small mountainous.SEMC of runoff pollutan COD and NH3-N in a small mountainous town was higherthan maximum concentration of Ⅴgrade of water quality. It affected water environment, and the surface runoff pollution should be emphasized.④Rainfall pollutant load of unit area for the same pollutant in same smallmountainous towns had a great difference. Rainfall pollutant load of unit area indifferent small mountainous towns had a great difference. Runoff frequency stands forpollution load probability. Annual runoff frequency curve indicates that mediumpollutant load had a highest probability of75%and low pollutant load together highpollutant load had a probability of only25%.⑤The comprehensive evaluation indices of drainage system for smallmountainous towns were selected and established by Delphi, the comprehensiveevaluation indices system of drainage system for small mountainous towns wasestablished. The indices weight was determined by Eigenvector method. Fuzzy MatterElement Analysis was choosed as a comprehensive evaluation method to establish anoptimization option model of drainage system for small mountainous towns. VisualBasic (VB) was utilized to develop a comprehensive evaluation model of software onFuzzy Matter Element Analysis. Taking a typical residential small mountainous town inChongqing as an example, the parameters of optimization model were calibrated.Bysoftware of drainage system based on fuzzy matter element analysis, the result showedthat the most suitable drainage system was complete separate system for residentialsmall towns under given conditions.Two typical small mountainous town were selectedand proved their drainage system by the optimization option model of drainage system. |
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