Numerical Simulation Study On Dissolved Oxygen In Heavily Polluted River In Mountainous City

Riversin Mountainouscity feature with fast discharge and quick release. Hydraulicstructures are often built for store water. Velocity of flowbecomesslowduring the dryseason resulting in poor self-purification capacity of water bodies. As the developmentof industrialization and urbanization,rivers werepolluted andbecome eutrophication withriparian vegetationdestroyed. Loss of ecological functions, water body becameblack-odor. Dissolved oxygen in water is the basis for the survival of plants andanimals.Reflecting the self-purification capacity of water bodies, dissolved oxygenis animportant indicator of the quality of the water body.Acknowledge the distribution ofdissolved oxygen in the river and the impact of external conditions changefor dissolvedoxygen are important basis of developing measures to protect river from black-odor andensure the health ofriver.Funiu Creek, a secondary river that flow into the Yangtze River is located inDadukou District, Chongqing.Funiu Creekis a typical mountainous river. In recent years,the riparian vegetation of the river has been destroyedwhich result in serious soilerosion. Water quality of the river is inferiorⅤwater, basically lost its ecologicalfunctions. Many hydraulic structures were built to storage water in Funiu creek, whichresult in slow flow velocity and poor self-purification capacity.In this study, MIKE11model was used to establish water quality model of theFuniu creek on the basis of detailed analysis of water pollution situation. The maincontents of the study and conclusions are as follows:①Quality and quantity of the wastewater flow into the river were investigated.Non-point source load was calculated based the land use type. The river was dividedinto four reaches according to hydrodynamic conditions of river.The pollution characterwas analyzed for each river reach based onwater quality data monitored during2012-2013.Single Factor Water Quality Identification Index was used to assesseachriver reach. The results showed that:Total nitrogen and total phosphorus are the mainpollutants. Ammonia pollution is much heavier in the downstream ofthe river.Theconcentration of CODMncan up to theⅤstandard in Environmental quality standards forsurface water.②NAM module in MIKE11model was used to established rainfall-runoff modelof Funiuxi Creek based onrunoff datameasuredduring1995-1999. Parameters sensitivityanalysis was conducted under three kinds of typical rainfall(abundant, normal and scarce)respectively. The results showed that:The correlation coefficient valuesof simulatedand observedrunoffare0.778and0.775in the upstream and downstream catchments respectively. The relative error oftotal volume betweensimulated and observed is8.24%. Umaxis a sensitive parameteraffecting the water balance under three typical rainfall conditions.③Water level and flow of Funiu creek were simulated by HD module coupled withthe NAM model.The result was calibrated according to observed data of3#cross-section. The sensitivity of bed resistance was analyzed. Simulation results showthat: the correlation coefficient of water level is0.73and Nash-Sufficient efficiencycoefficient is0.62. The correlation coefficient of flow is0.78. Nash-Sufficient efficiencycoefficient is0.60. Bed resistance has limited impact on water level.④AD and ECOLab module was used to simulate water quality with Level4template. Relative error of simulated and observed values of ammonia andBOD5are21.6%and20.7%relatively. Oxygen simulated value can reflect the actual changes inthe law. Model can be used to simulate the water quality of Funiu creek and getsatisfactory results. Algae in water are important factor in the impact of dissolvedoxygen. Respiration of animals and plantsplay important role in dissolved oxygenconsumption so as to sediment.⑤Water quality model was used to predict the impact of point source treatmentand water diversion schemes on water quality. Results show that:water quality get anobvious improvement after point source treated. The concentration of ammonia andBOD5can up to the Ⅴstandard in Environmental quality standards for surfacewater.Obvious improvement of water quality can get under the two different waterdiversion schemes. Using comprehensive Treatment program can get a better effect.There still comes the phenomenon that the concentration of dissolved oxygen blow2mg/L.At present, improving water body water quality and restoring ecosystem hasbecome the common goal of government and residents. Numericalsimulation methodwas used to analysis the interaction between dissolved oxygen and water pollutants andfind out the main impact factor. Pollution control and management can put forwardbased on the simulation results.