【作者】 王晓青；

【导师】 郭劲松；

【作者基本信息】 重庆大学 ， 市政工程， 2012， 博士

【摘要】 三峡水库次级河流回水区富营养化问题是当前三峡库区最为严重的生态环境问题之一。三峡大坝建成蓄水后，长江干流总体营养盐浓度变化并不显著，水质总体保持稳定。但由于水滞留时间的延长，长江支流水体富营养化有加重趋势，因水体富营养化出现了较大规模的水华现象。而水动力条件的改变是导致水体富营养化，加剧水华发生的最主要原因。因此，考虑水动力条件对水质污染和水体富营养化的影响及水华控制具有重要意义。在分析澎溪河流域气象、水文及污染特征和三峡蓄水后澎溪河水动力条件、水质等水环境因素的变化的基础上，构建SWAT与MIKE21耦合模型，研究调节坝的生态调度控制水体富营养化的可行性并提出优化调度方案。研究成果可为三峡水库支流回水区的富营养化控制提供理论依据和实践参考。论文主要研究内容如下：①澎溪河流域气象水文特征及回水区河道形态特征。澎溪河地区具备发生水体富营养化的光热条件，春夏之交是富营养化多发季节。澎溪河流域年际和年内的降水量、径流量分配不均匀。三峡水库蓄水后，澎溪河断面面积为1082-75126m²，水面宽度为57.60-2026.31m。河道断面面积和水面宽度沿程变化大，河道形态复杂。②澎溪河水质及富营养化现状。在收集野外监测数据的基础上分析环境条件和各污染物指标的相互关系，根据回水区的径流量、降水量，结合水温、气温、溶解氧（DO）、氮（N）、磷（P）、叶绿素a（Chla），化学耗氧量（COD）、生化需氧量（BOD₅）等指标的浓度值，分析了水污染与水文条件的关系。研究结果表明：季节性温度、降水量等因素是影响澎溪河水环境的首要原因,其次是三峡水库蓄水的影响，蓄水后水位的变化使回水区水环境因子发生变化：DO升高并趋于均匀分布，总氮（TN）峰值浓度略有下降，总磷（TP）峰值浓度略有增加，N/P值有减小的趋势。蓄水后的水文条件易导致水体富营养化的发生。从年内分析来看，高浓度的TN、TP容易出现在降水量大、流量大的丰水期；流量大于150m³/s或日平均降水量大于30mm的水文条件下容易测得高的TN、TP浓度值，但Chla含量较低；高含量的Chla容易出现在3-5月份澎溪河流量在35-45m³/s之间，且前期降水量不超过15mm的情况下。③三峡蓄水对污染物降解系数及水环境容量的影响。受天然因素和人工蓄水的影响，澎溪河水域污染物滞留时间及降解率的变化呈现出动态特征，回水区污染物降解系数为蓄水前1/20-1/10，直接影响着水环境容量的变化。采用一二维水动力模型相结合，对澎溪河7个功能区进行计算表明：蓄水后，COD_Mn水环境容量减少约15.6%,氨氮（NH₃-N）水环境容量减少量约12.2%，TP水环境容量减少约28.3%。④采用MIKE21水动力模型，研究三峡蓄水对澎溪河回水区水动力特征影响。三峡蓄水后，水位上升，澎溪河回水区段河道断面增宽，过水面积增加。在相同流量条件下，断面流速比天然状态下减小，流速与蓄水位成反比。蓄水前澎溪河各个断面的最小流速为0.01-0.19m/s，蓄水后最小流速为0.001-0.005m/s。蓄水后，渠马、高阳、黄石、双江大桥、河口五个断面的平均流速为蓄水前的1/2-1/100。依据本文对澎溪河水动力和水质特征的分析提出了水体类型划分：湖泊型流速<0.016m/s，过渡型流速为0.016-0.050m/s，河道型流速为>0.050m/s。水动力学条件的改变导致水质评价适用标准的改变，从而水质评价结果由蓄水前的Ⅱ-Ⅲ类达标水体变为超过Ⅱ-Ⅲ类水质的不达标水体。⑤采用SWAT分布式水文模型对澎溪河流域非点源污染负荷的研究。采用SWAT模型，根据流域的数字高程、土壤分类、植被分类、气象水文、水质等自然特征和行政区划、人口分布等社会经济状况的相关数据和资料，建立模型数据库。划分为25个计算子流域，225个水文相应单元（HRUs），模拟计算流域非点源污染负荷。在7-9月氮、磷负荷最大，丰水期氮平均为928.67吨/月，磷平均为173.47吨/月；在12月至次年1月氮、磷负荷最小，枯水期氮平均为61.91吨/月，磷平均为11.56吨/月。⑥构建SWAT模型与MIKE21耦合模型，预测水质及水体富营养化。根据三峡水库的调蓄过程，在175m高水位、小流量、低污染负荷和145m低水位、大流量、高污染负荷的两种设计条件下模拟澎溪河水体断面平均COD_Mn、TN、TP浓度和Chla含量，澎溪河回水段从上游到下游的COD_Mn、TN、TP浓度有增加的趋势，在接近河口处有趋同于长江水污染物浓度的趋势。145m低水位的大流量、高污染负荷设计条件下Chla含量较高，在弯道下游和河道水面开阔的高阳、双江大桥断面的流速减缓区段，出现Chla含量峰值。拟合澎溪河水体流速及Chla含量相关关系，分别在枯丰两种设计条件下建立水体流速（V）与Chla（S）含量的相关关系式，分别为S=0.1860·V^1.6820（相关系数r²=0.8380）和S=10.8449·V^-0.2939（相关系数r²=0.8380）。模拟结果表明：加大水体流速有利于抑制Chla含量。通过改变水动力条件控制富营养化具有可行性。⑦依托已建的澎溪河生态调节坝，提出了澎溪河水华控制生态调度方案。根据河流流速与Chla含量的相关性，根据澎溪河水动力学特征和水利工程的控制约束条件，建立了生态调度模型，模拟计算并提出了3-6月控制水华发生机率的调节坝最优化调度运行方案，使生态调节坝下游回水区的断面平均Chla含量控制在20ug/L以下从而达到控制水华的目的。更多还原

【Abstract】 The eutrophication of the secondary river in the Three Gorges reservoir is one ofthe most severe ecological environmental problems currently in china. After theimpoundment of the Three Gorges reservoir, the nutrient concentrations did not changesignificantly in the Yangtze River and the water quality remained stable in general.However due to water retention time extension, the eutrophication in the secondaryriver shows increased trend, the phenomenon of algae bloom has occurred many times.The change of hydrodynamic condition was the main reason of the water eutrophicationand algae bloom, therefore, it is significant to study the influence of the hydrodynamiccondition on water pollution concentrations and eutrophication in order to control algaebloom.In this paper I analyzed the meteorological condition, water hydrological conditionand pollution load in the Pengxi catchment, the change of water environmental factorssuch as hydrodynamic condition and the water quality in the Pengxi River. Based onthis data, I built the SWAT and MIKE21coupled models to study the feasibility of damregulation to control eutrophication, and to put forward proposal of optimizationoperation schemes. My research provided scientific basis for the water environment andeutrophication control in the backwater area of the Three Gorges reservoir tributary.This research is summarized in the following aspects:①The characteristics of meteorology, hydrology in the Pengxi catchment andbackwater morphology.In the Pengxi catchment the photothermal conditions meet the need of the watereutrophication which occurs frequently at the end of spring and the beginning of thesummer. The rainfall and runoff distribution are uneven. The Pengxi River morphologyis complicated, the cross section areas are from1082m²to75126m²and water surfacewidths vary along the river are from57.60to2026.31m after the impoundment.②The current situation of water quality and eutrophication in the Pengxi River.I studied relations between environmental conditions and hydrodynamic conditionsbased on environmental monitoring data. In addition, I analyzed the relations betweenthe water pollution and hydrological factors based on the rainfall, runoff and the valuesof temperature, dissolved oxygen （DO）, nitrogen （N）, phosphorus （P）, chlorophyll-a（Chla）, chemical oxygen consumption（COD）, five-day biochemical oxygen demand （BOD₅）, etc. The results showed that the season factors such as temperature and rainfallwere the main influential factors of the water environment. The other factors are fromthe impoundment of the Three Gorges, and the change in water level due toimpoundment ultimately leads to the water environment change. The DO concentrationrose and tended to be even, the peak concentration of total nitrogen（TN） decreasedslightly and the peak concentration of total phosphorus （TP） increased slightly, and N/Pvalue had the tendency to decrease. After the impoundment the hydrological conditionswere helpful to form water eutrophication. The analysis of a year period showed that thehigh concentrations of TN and TP were easy to develop in the high precipitation andhigh discharge period. The high concentrations of TN and TP occurred under theconditions of runoff higher than150m³/s, or daily precipitation higher than30mm,however the concentrations of Chla were relatively low during this period. The highChla concentrations were easy to develop from March to May when the runoff is35-45m³/s and the early precipitation is below the15mm.③Effect of the Three Gorges reservoir impoundment on the pollutant degradationcoefficients and water environmental capacities of the Pengxi River.Affected by the natural factors and impoundment regulation, the pollutant retentiontime and the degradation rate in the Pengxi water presented dynamic characteristics.The pollutants degradation coefficients after the impoundment were1/20-1/10of thecoefficients before the impoundment, which affected the water environmental capacities.The results simulated by the1D-2D coupled model from seven water function divisionsshowed that after the impoundment of the Three Gorges, the COD_Mn capacity wasreduced by15.6%, the ammonia nitrogen（NH3-N） capacity was reduced by12.2%andthe TP capacity was reduced by28.3%within a year. Water hydrological conditionsafter the impoundment were favorable for the eutrophication in the Pengxi River.④The study on the effect of the impoundment on water dynamic characteristicsin the Pengxi backwater area simulated by the MIKE21model.After the impoundment of Three Gorges project, water depth and the area andwidth of river cross section from the Pengxi backwater water increased. On thecondition of the same runoff, flow rate was reduced as compared to the naturalcondition, and it was inversely proportional to the water level. Before the impoundmentthe minimum flow rate is0.01-0.19m/s and after the impoundment the minimum flowrate is0.001-0.005m/s in the Pengxi backwater. The mean flow rates of five sectionsfrom Quma, Gaoyang, Huangshi, Shuangjiang bridge and Hekou after impoundment were1/2-1/100of those before the impoundment. According to the hydrodynamicconditions and the water quality of the river, the water type was defined as thefollowing: the flow rate of lake type is lower than0.016m/s, the flow rate of thetransition type is0.016-0.050m/s, and the flow rate of the river type is greater than0.050m/s. The dynamic change of water type lead to the change of the applicable waterquality evaluation standards, thus the evaluation result of II-III water quality standardturns to exceeded II-III water quality standard.⑤The study on the non-point pollution load in the Pengxi catchment based on theSWAT distributed hydrological model.Based on the data from digital elevation, soil types, vegetation types, meteorology,hydrology, water quality, administrative divisions, population distribution, etc., thedatabase was set up with these as the SWAT input conditions. The Pengxi catchmentwas divided into twenty five subcatchments and225hydrological response units（HRUs）. The results simulated by SWAT showed that Nitrogen and Phosphorus loadsfrom July to September were high, the mean monthly loads of Nitrogen and Phosphoruswere928.67tons and173.47tons respectively in the flood period; The Nitrogen andPhosphorus loads from December to February is low, the mean monthly loads ofNitrogen and Phosphorus were61.91tons and11.56tons respectively in the dry period.⑥The SWAT and MIKE21models were coupled to predict the water quality andwater eutrophication.I simulated the average COD_Mn, TN, TP concentrations and Chla content along thePengxi River on two design conditions:1)175m high water level with low flow and lowpollutant load;2)145m low level with high flow and high pollutant load. COD_Mn, TN,TP concentrations from upstream to downstream tended to increase, and the waterquality at the estuary trended toward the Yangtze water quality. In the period of145mlow water level with large flow and high pollutant load, the Chla content was high. Inthe curve or wide surface sections such as Gaoyang or Shuangjiang Bridge, the flowrate was slow and Chla content was high.The correlation of flow rate （V） and Chla content （S） was fitted under the twodesign conditions, the equations were S=0.1860·V^1.6820（related coefficientr²=0.8380）and S=10.8449·V^-0.2939（related coefficient r²=0.8380） respectively. Thesimulated results showed that the increase of flow rate tended to keep down the Chlacontent. It is feasible to control water eutrophication through the hydrodynamicconditions. ⑦The ecological regulation schemes put forward relied on the Xiaojiangecological regulating dam.Based on the correlation between the flow rate and Chla content, the constraintconditions of hydrodynamic feature and hydraulic project, I established the ecologicalscheduling models. And I put forward the optimization schemes from March to June tocontrol Chla content of lower than20ug/L for the purpose of controlling watereutrophication.更多还原