Hydrodynamic And Water Quality Modeling For The Middle And Upper Of Minjiang River

Watershed models have been proved to be an viable tool for integrated watershed management,which can analyze the influence of human activities on watershed,thereby providing effective management alternative.Min River as the mother river of Fujian,is the water sources for industry,agriculture and drinking of more than 12 million people in Nanping,Sanming,Ningde,Fuzhou,Quanzhou and other cities.Whether the water quality achieved the standards or not is related to 10 million residents' health.However,the simulation of water quality in the middle and upper reaches of the Minjiang River is rarely reported.The water environment model in the middle and upper of Minjiang River Basin was built providing technical support for integrated management of Minjiang River Basin.Insite monitoring,lab measurement,modeling,GIS and scenario analysis were coupled in this study to construct semi-distributed watershed model HSPF and Hydrodynamic and water quality model EFDC,so as to simulate the middle and upper reaches of the Minjiang River.The specific results are as follows:Firstly,the temporal and spatial variation of water quality in the middle and upper reaches of Minjiang River was identified.Analysing the water quality of 2003-2012,the concentration of disolved oxygen in Taxia,You River and Shuikou Bridge in the last 10 years ranged from 5 mg/L to 8 mg/L showed a slightly decreasing trend and reach the Class III water standards.Gutian River showed an increasing trend,which was between 1.2 mg/L and 8 mg/L,the lowest concentration is lower than the Class V water standards.The concentration of ammonia nitrogen in Taxia and Shuikou Bridge showed a decreasing trend but almost below Class III water standards.The concentration of ammonia nitrogen in Gutian River was almost unchanged,with an averege value of 2.28 mg/L and its concentration was higher than Class V water standards.The concentration of total phosphorus in Taxia and Shuikou Bridge showed an slight upward trend.The concentration of total phosphorus in You River and Gutian River showed a slight decrease,and the total phosphorus concentration in Gutian River was abnormal,with a maximum of 0.81 mg/L higher than Class V water standards.The rest reach the Class III water standards.Analysis the sampled water quality,the concentration of ammonia,total phosphorus and chlorophyll-a in the cage culture area was generally higher than that of the non-network,and the concentration of disolved oxygen in the cage culture area was lower than that in the non-cage culture area.The concentration of ammonia in Gutian River was higher than that in the upper reaches of Min River.Secondly,the watershed database of Min River Basin is constructed,including DEM,landuse,soil,hydrological water quality data and meteorological data.The water environment analysis model of the upper and middle reaches of the Minjiang River includes two parts:the first part is the construction of the HSPF of the three tributaries(Shaxi,Jianxi and Fu Tunxi),which are generalized into 380 sub-basins;the second part is EFDC model constructing from Taxia which is the confluence of Shaxi,Jianxi and Futunxi including the two-dimensional EFDC model of the reservior area,which are generalized to 1750 grids and one-dimensional EFDC model from Shaxikou to the mainstream which is generalized to 500 grids.Thirdly,the HSPF model in the middle and upper reaches of Min River was built with NSE>0.7.With the weather data and flow data from 2005 to 2008,the HSPF model of middle and upper reaches of Min River was calibrated.The Nash coefficients of the daily flow calibration stage of Shaxi,Fu Tunxi and Jianxi were 0.784,0.774 and 0.782 respectively.The HSPF model was validated with meteorological data and flow data from 2009 to 2012,and the Nash coefficients of the daily runoff verification stage were 0.745,0.782 and 0.737.Fourthly,EFDC model in the middle and upper reaches of Min River was built with has finished calibrating and validating hydrology and water quality with the Median Error(ME)of daily flow is less than 0.1,and the ME of DO,NH3-N and TP is mostly less than 0.4 which means that the EFDC works well.With the hydrological and water quality data from 2009 to 2010,the EFDC model of middle and upper reaches of Min River was established and the model was calibrated.The results showed that the ME of the daily flow of the model was 0.013,0.0184 and 0.0184,respectively,and ME of DO in Yuxi,Taixia and Shuikou Bridge was 0.0268,0.001,0.143 and 0.331 respectively.ME of NH3-N in Yuxi,Tower,Zhanghuban,Shuikou Bridge is 0.00335,0.0718,0.705 and 0.327 respectively;ME of TP in Youxi,Taxia,Zhanghuban and Shuikou Bridge was 0.00268,0.08,0.438 and 0.295,respectively.With the hydrological and water quality data from 2011 to 2012,the EFDC model of middle and upper reaches of Min River was validated.ME of the daily runoff of the Taxia,Youxi and Shuikou Bridge was 0.0084,0.017 and 0.0184,respectively.The DO in the Youxi,Taxia,Zhanghuban and Shuikou Bridge,the water outlet ME of the bridge was 0.0268,0.001,0.141 and 0.331 respectively.ME of NH3-N in Youxi,Taxia,Zhanghuban and Shuikou Bridge was 0.0232,0.00168,0.298 and 0.388 respectively.ME of TP in the Youxi,Taxia,Zhanghuaban and Shuikou Bridge,the median error was 0.00828,0.00054,0.326 and 0.296.The simulation trend and the measured value change trend are basically consistent,the simulation effect is good,the median error is within the acceptable range,through the model of the calibration and validation,to meet the technical requirements of forecasting and early warning.Finally,combined with the scenario design,the calibrated HSPF and EFDC model was used to simulate the influence of hydrological condition change,cage culture and controlling Gutianxi water quality on the water quality of Shuikou reservoir area,and provided a quantitative basis for water quality control in Shuikou reservoir area.According to the characteristics of the Minjiang River Basin,three scenarios were developed.The results showed that:a)During the wet season,the low dissolved oxygen in Gutian River could affect the water quality of the main stream,resulting in low dissolved oxygen,causing dead fish events,but the effect of normal season and dry season on the Minjiang River will not be significant;b)After the cage culture of You River is removed,the water quality of the Minjiang River reaches a significant change,the DO concentration is increased by 3%-10%,the NH3-N concentration is reduced by 5%-17%,TP concentration decreased by 6%-21%;c)Reducing the concentration of ammonia in the Gutianxi,ammonia concentration of Shuikou reservoir in Min River has a big change.If ammonia concentration in Shuikou reservoir area has to reache Class III water quality,Gutianxi ammonia nitrogen concentration can not exceed 2.14 mg/L.The results of the relevant scenario analysis showed that the effective control of the water quality in Gutian and Youxi can effectively improve the water quality of the reservoir area and its downstream.