Research On The River Assimilative Capacity And The Rainwater Overflow Impact

Water is an essential resource for human life and production. As the industrialsociety advances, water problems—mainly water shortage and water pollution, aregetting increasingly severe. Under the condition that water resource volume can’tincrease by a large margin, controlling water pollution becomes the priority inalleviating water problems. Currently, the adoption of combined intercepting sewernetwork in most cities, which is liable to produce overflow at the initial stage of rainfalland lead to river pollution, gravely compounds the difficulty of water environmenttreatment. With Jiaozhou’s moat and the drainage pipe system in its service zone as thestudy subjects, this thesis analyzes how initial rainwater overflow influences the river’sassimilative capacity in combined intercepting sewer network in terms of itsassimilative capacity and initial rainwater overflow, and aims to provide data supportsfor the optimization of combined drainage network and river treatment in the old city.When calculating and analyzing the river’s assimilative capacity, the thesis adoptsthe river water quality model and delves into the influences of different calculationmethods on the calculation results under specific hydrologic design conditions andwater quality. Besides, it also explores the result differences in the river’s assimilativecapacity when factors like upstream background concentration, discharge modes ofdifferent pollution sources, and fracture surface are taken into consideration. Therefore,this thesis provides sound technical supports for studies on river’s assimilative capacityas well as water environment protection, and obtains the assimilative capacity value ofthe study subjects by case study.For overflow in rain spell, this thesis selects the SWMM model as the drainagemodel in pipe network simulation after comparative analysis. On the basis of data andfield survey, the thesis finishes the generalization of the pipe network and the catchmentarea, calibrates several simulation parameters, and completes the model construction.Then, it carries out simulation and calculation on the operation of pipe network indifferent rainfall reoccurrence periods, and fully considers the influence of pipe network deposit on its operation in rainfall period. In order to tackle the hydraulic problems inthe simulated operation like node overflow and section overload, node elevationregulation and pipe diameter regulation are adopted in the optimization stage.By integrating the river’s assimilative calculation results and simulated overflow ofpipe network in rainfall period, this thesis analyzes the overflow rules of rainwater andquantitatively analyzes the impact of overflow concentration changes of COD, NH4+-N,TP, and TSS on the river’s assimilative capacity. Then, according to the river’s overflowpollution in the analysis, the thesis proposes such alleviating methods as enlarging theinterception ratio of the intercepting well and increasing greening area. In addition,corresponding SWMM rain spell simulation is performed to justify the feasibility ofthese methods in solving overflow pollution and to provide technical supports forstudies on river’s assimilative capacity and water environment protection.