CN114662422A - Construction method of thermal stratification reservoir thermocline dissolved oxygen prediction model - Google Patents

Construction method of thermal stratification reservoir thermocline dissolved oxygen prediction model Download PDF

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CN114662422A
CN114662422A CN202210350380.6A CN202210350380A CN114662422A CN 114662422 A CN114662422 A CN 114662422A CN 202210350380 A CN202210350380 A CN 202210350380A CN 114662422 A CN114662422 A CN 114662422A
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马冰
董飞
彭文启
刘晓波
黄爱平
王伟杰
司源
陈学凯
王威浩
黄智华
杜霞
李今今
雷阳
廉秋月
杨晓晨
邓欣
邓秘
朱志鹏
赵彦芳
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Abstract

The invention discloses a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model, which comprises the following steps: s1, acquiring actually measured terrain data of the thermal stratification lake reservoir to generate a Cartesian calculation grid; s2, obtaining the discretized bottom elevation of each layer of grids according to the actually measured terrain data; s3, constructing a three-dimensional hydrodynamic model for simulating a thermal stratification reservoir hydrodynamics process; s4, constructing a temperature field model according to a temperature transport equation and a water surface heat exchange equation; s5, constructing an eutrophication model according to a mass conservation equation and a dissolved oxygen kinetic equation of a water quality variable; s6, forming a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir by adopting a three-dimensional hydrodynamic model, a temperature field model and an eutrophication model; s7, predicting dissolved oxygen of a thermocline of the thermal stratification lake reservoir by adopting a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir, judging whether the dissolved oxygen meets preset conditions or not by S8, determining whether an minimum value dissolved oxygen region exists in the thermocline of the thermal stratification reservoir, and providing technical support for protecting the ecological environment of the water in the lake reservoir.

Description

Construction method of thermal stratification reservoir thermocline dissolved oxygen prediction model
Technical Field
The invention relates to the technical field of dissolved oxygen of a thermal stratification reservoir, in particular to a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model.
Background
The lake and reservoir dissolved oxygen is one of the important factors for maintaining the ecological safety of the water, reflects the balance between various reoxygenation and oxygen consumption functions, and is the premise on which aquatic organisms live and the health of an aquatic ecosystem. When the temperature rises in summer, the heat is unevenly distributed in the vertical direction, so that the reservoir water body is thermally layered. During this period, the thermocline and the isothermal layer are prone to form an anoxic or anaerobic reducing environment. Wherein, the oxygen deficiency of the thermocline can form a thermocline dissolved oxygen minimum phenomenon, and observation reports are already carried out in a plurality of lake and reservoir water bodies in different areas, thereby bringing adverse effects to the ecological environment of the lakes and reservoirs.
The dissolved oxygen in the thermocline is subjected to combined action of high oxygen consumption and low vertical mixing, and the reason of the high oxygen consumption is still presumed to be related to mechanisms such as plankton respiration, external substance input, turbidity-related respiration or sediment decomposition and the like, so that the dynamic change of the dissolved oxygen in the thermocline is difficult to predict. In the prior art, the simulation and prediction of the dynamic process of the low dissolved oxygen in the temperature stagnation layer are mostly focused, so that a construction method of a prediction model of the dissolved oxygen in the thermocline layer of the thermal stratification reservoir is urgently needed. The method for constructing the thermal stratification reservoir thermocline dissolved oxygen prediction model provides an effective means for deeply knowing the thermocline hypoxia mechanism and provides a scientific basis for the ecological environmental protection of the water in the lake reservoir.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a construction method of a prediction model of dissolved oxygen in a thermocline reservoir, and solves the problem that the evolution cause of the dissolved oxygen in the thermocline reservoir is still unclear in the prior art.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model is provided, and comprises the following steps:
s1: acquiring actual measurement terrain data of the thermal stratification lake reservoir to generate a multi-layer Cartesian calculation grid;
s2: obtaining the discretized bottom elevation of each layer of computational grid by adopting a neighborhood method according to the actually measured topographic data;
s3: constructing a three-dimensional hydrodynamic model for simulating the hydrodynamics process of the thermal stratification reservoir based on the bottom elevation according to a continuity equation;
s4: constructing a temperature transport equation according to the thermocline temperature of the thermal stratification reservoir and the solar short wave radiation intensity; constructing a water body surface heat exchange equation according to the surface heat exchange rate and the surface heat coefficient; adopting a temperature transport equation and a water surface heat exchange equation to form a temperature field model;
s5: constructing a mass conservation equation of the water quality variable according to the water quality variable concentration; constructing a dissolved oxygen kinetic equation according to the concentration of the dissolved oxygen, and adopting a mass conservation equation of water quality variables and the dissolved oxygen kinetic equation to form a eutrophication model;
s6: forming a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir by adopting a three-dimensional hydrodynamic model, a temperature field model and an eutrophication model;
s7: acquiring flow information and meteorological conditions of the thermal stratification lake reservoir, and predicting dissolved oxygen of a thermocline of the thermal stratification lake reservoir by adopting a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir;
s8: and judging whether the dissolved oxygen meets the preset condition, if so, a minimum dissolved oxygen region exists in the thermocline of the thermal stratification reservoir, and increasing the dissolved oxygen amount of the thermocline, otherwise, the minimum dissolved oxygen region does not exist in the thermocline of the thermal stratification reservoir.
Further, the continuity equation is:
Figure BDA0003579791620000021
Figure BDA0003579791620000022
wherein ,mx，myAll are coordinate transformation coefficients, and under Cartesian coordinates, the transformation coefficients are equal to 1; zeta is the water surface elevation relative to the reference height in m; h is total water depth, unit m; u, v and w are depth average velocity components in x, y and z directions respectively, and the unit is m/s;
the three-dimensional hydrodynamic model comprises momentum equations in the x direction, the y direction and the z direction, wherein the momentum equation in the x direction is as follows:
Figure BDA0003579791620000031
the momentum equation in the y direction is:
Figure BDA0003579791620000032
the momentum equation in the z direction is:
Figure BDA0003579791620000033
wherein, (x, y) is a curve-orthogonal coordinate in the horizontal direction; z is a vertical sigma coordinate; (u, v) is the horizontal velocity component in the (x, y) direction, in m/s; patmIs atmospheric pressure in Pa; ρ is a reference density ρ0Additional hydrostatic pressure below; b is buoyancy; f is a Coriolis coefficient and covers the curvature acceleration of the grid; a. theHIs the horizontal momentum diffusion coefficient, unit m2/s；AvIs the vertical turbulent viscosity coefficient, unit m2/s；cpThe vegetation resistance coefficient; dpIs a projected vegetation area intersecting the flow per horizontal area; s. theu，SvIs the source and sink term of the momentum equation in the x and y directions respectively, and the unit m2/s2；SlIs the source-sink term of the conservation of mass equation, unit m2/s2(ii) a S is salinity, unit ng/L; t is temperature in units; c is the total suspended inorganic particle concentration in g/m3(ii) a P and Q are mass flux components in the x and y directions, respectively,unit m2/s。
Further, the calculation formula of the vertical turbulence viscosity coefficient is as follows:
Figure BDA0003579791620000041
wherein ,
Figure BDA0003579791620000042
a stable viscosity coefficient; q is the turbulence intensity in m2/s2(ii) a l is the turbulent length scale in m;
the calculation formula of the turbulence intensity q and the turbulence length scale l is as follows:
Figure BDA0003579791620000043
Figure BDA0003579791620000044
Figure BDA0003579791620000045
wherein ,SbIs a source and sink item of the turbulence intensity equation; slIs a source and sink item of the turbulent length scale equation; a. theqThe vertical turbulent diffusion coefficient of the turbulent intensity equation; a. theqlThe vertical turbulent diffusion coefficient of the turbulent length scale equation; e1＝1.8，E2＝1.0，E3＝1.8，E4＝1.33，E5＝0.25。
Further, the temperature transfer equation is:
Figure BDA0003579791620000051
wherein T is temperature in units; a. thebThe vertical turbulent diffusion coefficient is adopted,unit m2S; i is the solar short wave radiation intensity and the unit is W/m2；STIs the source and sink term of heat exchange, unit J/s;
the water body surface heat exchange equation is as follows:
Haw＝-Kaw(Ts-Te)
wherein ,HawFor surface heat exchange rate, in W/m2；KawIs the surface thermal coefficient in W/(m)2·℃)；TsIs the water surface temperature in units;
the expression for the light intensity in the water column is:
Figure BDA0003579791620000052
Figure BDA0003579791620000053
Iws＝I0Sfmin{exp[-Ke，me(Hrps-H)]，1}min{exp[-Ke，iceHice]}
wherein ,KeIs extinction coefficient with unit of 1/m; z is the depth below the water surface in m; i iswsThe light intensity of the water surface, I0Is the intensity of solar radiation on the surface of the earth and has the unit of W/m2；SfIs a shading coefficient; hiceIs the ice thickness in m; k(e，ice)The extinction coefficient of the ice cover is 1/m; k(e，me)The extinction coefficient of vegetation immersed in water is 1/m; hrpsThe height of the submerged vegetation buds is m.
Further, the mass conservation equation of the water quality variable is as follows:
Figure BDA0003579791620000061
wherein C is water quality variable concentration, and the unit is mg/L; a. thex，Ay，AzThe vertical turbulent diffusion coefficients in the x, y and z directions are respectively, and the unit is m2/s；SCIs a source and sink item;
the first order kinetic expression is:
Figure BDA0003579791620000062
wherein k is the kinetic rate; r is a source/sink term due to external load and/or internal reaction;
the kinetic equation of dissolved oxygen is:
Figure BDA0003579791620000063
wherein ,CDOIs the dissolved oxygen concentration in g/m3(ii) a c, d, g and m respectively represent blue algae, diatom, green algae and macroalgae; PN (pseudo-noise)xPreference coefficient for class x algae to use ammonia nitrogen, 0 < PNx＜1；FCDxIs a part separated out in the form of dissolved organic carbon in the basic metabolism of the x-class algae;
Figure BDA0003579791620000064
is dissolved oxygen half-saturation constant, g/m, excreted by organic carbon in the dissolved state of algae of the x class3(ii) a AOCR is the oxygen consumption of organic carbon in respiration, and the value is 2.67; AONT is ammonia nitrogen nitrification oxygen consumption per unit mass, and the value is 4.33; ntt is the nitrification rate in units of 1/d; kHRThe unit is 1/d of the abnormal respiration rate of the dissolved organic carbon; cDOCIs the concentration of dissolved organic carbon in g/m3；KHCODIs the oxygen half-saturation constant in g/m3；KCODThe oxidation rate of COD is 1/d; cCODIs chemical oxygen demand concentration in g/m3；KRIs the reoxygenation coefficient with the unit of 1/d; cDOSIs saturated dissolved oxygen concentration in g/m3(ii) a SOD is sediment oxygen demand and has the unit of g/(m)2·d)；WDOThe unit is the external load in g/d.
Further, the preset conditions are as follows:
C1(z，t1)＝C0(z，t0)+ΔC(z，Δt)
Figure BDA0003579791620000071
Figure BDA0003579791620000072
Figure BDA0003579791620000073
Figure BDA0003579791620000074
wherein ,C1Is t1The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; c0Is t0The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; Δ C is a Δ t period (t)1-t0) The concentration of dissolved oxygen at the inner water depth z is changed, and the unit mg/L is; MOM is the minimum value of dissolved oxygen in the thermocline.
Predicting the dissolved oxygen concentration in a thermocline of the hot stratified reservoir according to a three-dimensional hydrodynamic water quality model of the hot stratified reservoir, wherein if the dissolved oxygen concentration in the thermocline of the hot stratified reservoir meets preset conditions, the dissolved oxygen in the thermocline is extremely small in the current thermocline of the hot stratified reservoir, and the dissolved oxygen concentration in the thermocline of the hot stratified reservoir needs to be adjusted manually; if the dissolved oxygen concentration of the thermocline of the thermal stratification reservoir does not meet the judgment condition, the phenomenon that the dissolved oxygen in the thermocline is extremely small does not exist in the thermocline of the thermal stratification reservoir, and the dissolved oxygen concentration in the thermocline of the thermal stratification reservoir is not adjusted.
Further, in step S1, the cartesian calculation grid includes a multi-layered horizontal rectangular grid, the multi-layered horizontal rectangular grid employing the SGZ coordinates in the vertical direction; the interval between two adjacent layers of horizontal rectangular grids is 1.5m-2.5m, the horizontal rectangular grids are below the water surface, and the interval between two layers of horizontal rectangular grids is 2.5 m; the horizontal rectangular grids are above the water surface, and the interval between the two layers of horizontal rectangular grids is 1.5 m.
Further, in step S3, the boundary conditions of the three-dimensional hydrodynamic model include upstream flow, downstream flow and meteorological conditions, such as atmospheric pressure, air temperature, relative humidity, rainfall, evaporation, solar radiation, cloud shading coefficient, wind speed and wind direction.
The invention has the beneficial effects that: the factors influencing the kinetic process of the dissolved oxygen in the lake and reservoir are numerous, and the factors interact with each other and influence each other. The temperature of water, dissolved oxygen, biomass and the rate of mass transfer in the thermocline have large gradients, so that the influence of different processes on the change of the dissolved oxygen is extremely difficult to quantify. The invention researches and develops a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model, considers the influence of a plurality of processes such as an algae biological process, an organic matter decomposition process, sediment oxygen consumption and the like on dissolved oxygen, can accurately simulate and predict the formation and development rule of the minimal dissolved oxygen phenomenon of the thermocline, is beneficial to explaining an oxygen consumption mechanism and predicting future development, is an indispensable tool for researching and driving and influencing the change factors of the dissolved oxygen of the thermocline of the lake and reservoir, and can provide technical support for the ecological environment protection of the water of the lake and reservoir.
Drawings
FIG. 1 is a flow chart of a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model.
Fig. 2 is a cross-sectional view of a Panjiakou reservoir computing grid.
FIG. 3 is a vertical section of a Panjiakou reservoir grid.
FIG. 4 is a terrain elevation difference diagram of a Panjiakou reservoir.
Fig. 5 is a schematic diagram of the upstream and downstream boundary conditions of the pan jiakou reservoir.
Fig. 6 is a comparison graph of the water level simulation value and the measured value of the pan family inlet reservoir.
Fig. 7 is a comparison graph of the measured value and the simulated value of the water temperature of the pan family reservoir.
FIG. 8 is a graph showing the comparison between the simulated dissolved oxygen value and the measured value in the Panjiakou reservoir.
FIG. 9 is a distribution characteristic diagram of dissolved oxygen minimum phenomenon in a thermocline and a thermocline of a Panjiakou reservoir.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
As shown in fig. 1 to fig. 1, the invention provides a method for constructing a prediction model of dissolved oxygen in a thermocline of a thermal stratification reservoir, taking a panjiakou reservoir as an example, the method comprises the following steps:
s1: and acquiring actual measurement terrain data of the thermal stratification lake reservoir to generate a Cartesian computational grid. As shown in fig. 2 to fig. 3, based on the actual measurement topographic data of the pan jiakou reservoir, rectangular grids of 200m × 200m are adopted in the horizontal direction, and the total number of the grids is 1911. And dividing 38 layers vertically by adopting an SGZ coordinate, wherein the interlayer spacing is 1.5-2.5 m, the interlayer spacing of two layers below the water surface is 2.5m, and the spacing of the rest layers is 1.5 m.
S2: obtaining the discretized bottom elevation of each layer of computational grid by adopting a neighborhood method according to the actually measured topographic data; taking the actual measurement of the terrain in the Panjia Kouchu area of 2016 as an example, the calculation grids of step S1 are differentiated, and the result of the terrain elevation difference is shown in FIG. 4.
S3: constructing a three-dimensional hydrodynamic model for simulating the hydrodynamics process of the thermal stratification reservoir based on the bottom elevation according to a continuity equation;
Figure BDA0003579791620000101
Figure BDA0003579791620000102
wherein ,mx，myAll are coordinate conversion coefficients, and under Cartesian coordinates, the conversion coefficients are equal to 1; zeta is the water surface elevation relative to the reference height in m; h is total water depth, unit m; u, v and w are depth average velocity components in x, y and z directions respectively, and the unit is m/s;
the three-dimensional hydrodynamic model comprises momentum equations in the x direction, the y direction and the z direction, wherein the momentum equation in the x direction is as follows:
Figure BDA0003579791620000103
the momentum equation in the y direction is:
Figure BDA0003579791620000104
the momentum equation in the z direction is:
Figure BDA0003579791620000105
wherein, (x, y) is a curve-orthogonal coordinate in the horizontal direction; z is a vertical sigma coordinate; (u, v) is the horizontal velocity component in the (x, y) direction, in m/s; patmIs atmospheric pressure in Pa; ρ is a reference density ρ0Additional hydrostatic pressure below; b is buoyancy; f is a Coriolis coefficient covering the curvature acceleration of the grid; a. theHIs the horizontal momentum diffusion coefficient, unit m2/s；AvIs the vertical turbulent viscosity coefficient, unit m2/s；cpIs the vegetation resistance coefficient; dpIs a projected vegetation area intersecting the flow per horizontal area; su，SvIs the source and sink term of the momentum equation in the x and y directions respectively, and the unit m2/s2；SlIs the source-sink term of the conservation of mass equation, unit m2/s2(ii) a S is salinity, unit ng/L; t is temperature in units; c is the concentration of total suspended inorganic particles in g/m3(ii) a P and Q are each x,mass flux component in y-direction, unit m2/s。
The calculation formula of the vertical turbulence viscosity coefficient is as follows:
Figure BDA0003579791620000111
wherein ,
Figure BDA0003579791620000112
a stable viscosity coefficient; q is the turbulence intensity in m2/s2(ii) a l is the turbulent length scale in m;
the calculation formula of the turbulence intensity q and the turbulence length scale l is as follows:
Figure BDA0003579791620000113
Figure BDA0003579791620000114
Figure BDA0003579791620000115
wherein ,SbIs a source and sink item of the turbulence intensity equation; s. thelIs a source and sink item of the turbulent length scale equation; a. theqThe vertical turbulent diffusion coefficient of the turbulent intensity equation; a. theqlThe vertical turbulent diffusion coefficient of the turbulent length scale equation; e1＝1.8，E2＝1.0，E3＝1.8，E4＝1.33，E5＝0.25。
Taking the pan house outlet reservoir as an example, the related parameters such as horizontal and vertical vortex viscosity coefficients and diffusion coefficients in the hydrodynamic model are calibrated, a pan house outlet three-dimensional reservoir hydrodynamics model is constructed, and the comparison result of the water level simulation value and the measured value is shown in fig. 6.
S4: constructing a temperature transport equation according to the thermocline temperature of the thermal stratification reservoir and the solar short wave radiation intensity; constructing a water body surface heat exchange equation according to the surface heat exchange rate and the surface heat coefficient; adopting a temperature transport equation and a water surface heat exchange equation to form a temperature field model;
the temperature transport equation is:
Figure BDA0003579791620000121
wherein T is temperature in units; a. thebIs a vertical turbulent diffusion coefficient in m2S; i is the solar short wave radiation intensity and the unit is W/m2；STIs the source and sink of heat exchange, and the unit is J/s;
the water body surface heat exchange equation is as follows:
Haw＝-Kaw(Ts-Te)
wherein ,HawFor surface heat exchange rate, in W/m2；KawIs the surface thermal coefficient in W/(m)2·℃)；TsIs the water surface temperature in units;
the expression for the light intensity in the water column is:
Figure BDA0003579791620000122
Figure BDA0003579791620000131
Iws＝I0Sfmin{exp[-Ke，me(Hrps-H)]，1}min{exp[-Ke，iceHice]}
wherein ,KeIs extinction coefficient with unit of 1/m; z is the depth below the water surface in m; I.C. AwsThe light intensity of the water surface, I0Is the intensity of solar radiation on the surface of the earth, and has the unit of W/m2；SfIs a shading coefficient; hiceIs the ice thickness in m; k(e，ice)Is an ice coverThe unit of the extinction coefficient of (2) is 1/m; k(e，me)The extinction coefficient of vegetation immersed in water is 1/m; hrpsThe height of the submerged vegetation buds is m. Taking the pan family mouth reservoir as an example, parameters such as extinction coefficient, riverbed temperature, thickness of an active bed temperature layer and the like are calibrated based on the constructed pan family mouth reservoir three-dimensional hydrodynamic model, a pan family mouth reservoir temperature field model is constructed, and a comparison result of a water temperature simulation value and an actual measurement value is shown in fig. 7.
S5: constructing a mass conservation equation of the water quality variable according to the water quality variable concentration; constructing a dissolved oxygen kinetic equation according to the concentration of the dissolved oxygen, and adopting a mass conservation equation of water quality variables and the dissolved oxygen kinetic equation to form a eutrophication model;
the mass conservation equation of the water quality variable is as follows:
Figure BDA0003579791620000132
wherein, C is the variable concentration of water quality, and the unit is mg/L; a. thex，Ay，AzThe vertical turbulent diffusion coefficients in the x, y and z directions are respectively, and the unit is m2/s；ScIs a source and sink item;
the first order kinetic expression is:
Figure BDA0003579791620000141
wherein k is the kinetic rate; r is a source/sink term due to external load and/or internal reaction;
the dissolved oxygen kinetic equation is:
Figure BDA0003579791620000142
wherein ,CDOIs the dissolved oxygen concentration in g/m3(ii) a c, d, g and m respectively represent blue algae, diatom, green algae and macroalgae; PN (pseudo-noise)xUse of ammonia nitrogen bias for x-class algaeGood coefficient, 0 < PNx＜1；FCDxIs a part separated out in the form of dissolved organic carbon in the basic metabolism of the x-class algae;
Figure BDA0003579791620000143
is dissolved oxygen half-saturation constant, g/m, excreted by organic carbon in the dissolved state of algae of the x class3(ii) a AOCR is the oxygen consumption of organic carbon in respiration, and the value is 2.67; AONT is ammonia nitrogen nitrification oxygen consumption per unit mass, and the value is 4.33; nit is the nitration rate, and the unit is 1/d; kHRThe unit is 1/d, which is the abnormal breathing rate of dissolved organic carbon; cDOCIs the concentration of dissolved organic carbon, and has a unit of g/m3；KHCODIs the oxygen half-saturation constant in g/m3；KCODThe oxidation rate of COD, l/d; cCODIs chemical oxygen demand concentration, and has unit of g/m3；KRIs the reoxygenation coefficient with the unit of 1/d; cDOSIs saturated dissolved oxygen concentration in g/m3(ii) a SOD is sediment oxygen demand with the unit of g/(m)2·d)；WDOIs the external load in g/d.
Taking the pan family mouth reservoir as an example, based on the constructed three-dimensional hydrodynamic model and the temperature field model of the pan family mouth reservoir, a pan family mouth reservoir eutrophication model is constructed by calibrating a plurality of water quality parameters such as the growth rate of algae, the hydrolysis rate of particles and the mineralization rate of dissolved state, the maximum value and the minimum value of suitable temperature, the sedimentation rate of organic matters and the like, and the comparison result of the dissolved oxygen simulation value and the measured value is shown in fig. 8.
S6: and forming a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir by adopting a three-dimensional hydrodynamic model, a temperature field model and an eutrophication model.
S7: and acquiring flow information and meteorological conditions of the thermal stratification lake reservoir, and predicting dissolved oxygen of a thermocline of the thermal stratification lake reservoir by adopting a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir.
S8: and judging whether the dissolved oxygen meets the preset condition, if so, a minimum dissolved oxygen region exists in the thermocline of the thermal stratification reservoir, and increasing the dissolved oxygen amount of the thermocline, otherwise, the minimum dissolved oxygen region does not exist in the thermocline of the thermal stratification reservoir.
The preset conditions are as follows:
C1(z，t1)＝C0(z，t0)+ΔC(z，Δt)
Figure BDA0003579791620000151
Figure BDA0003579791620000152
Figure BDA0003579791620000153
Figure BDA0003579791620000154
wherein ,C1Is t1The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; c0Is t0The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; Δ C is a Δ t period (t)1-t0) The concentration of dissolved oxygen at the inner water depth z is changed, and the unit mg/L is; MOM is the minimum value of dissolved oxygen in the thermocline.
Predicting the dissolved oxygen concentration in a thermocline of the hot stratified reservoir according to a three-dimensional hydrodynamic water quality model of the hot stratified reservoir, wherein if the dissolved oxygen concentration of the thermocline of the hot stratified reservoir meets preset conditions, the dissolved oxygen concentration of the thermocline in the current thermocline of the hot stratified reservoir is extremely small, and the dissolved oxygen concentration of the thermocline of the hot stratified reservoir needs to be adjusted manually; if the dissolved oxygen concentration of the thermocline of the thermal stratification reservoir does not meet the judgment condition, the phenomenon that the dissolved oxygen in the thermocline is extremely small does not exist in the thermocline of the thermal stratification reservoir, and the dissolved oxygen concentration in the thermocline of the thermal stratification reservoir is not adjusted.
Taking the Panjiakou reservoir as an example, according to the constructed three-dimensional hydrodynamic water quality model of the Panjiakou reservoir, the formation and development rules of the phenomenon of minimum dissolved oxygen in the thermocline are predicted. The phenomenon of minimal dissolved oxygen in the thermocline appears in a thermal stratification stable period (7 months-9 months), the formation period is 7 months-8 months, the development period is 9 months, and the minimal dissolved oxygen region in the thermocline gradually disappears along with the subsidence of the dissolved oxygen in a 10-month manner. The minimum value and position of dissolved oxygen in thermocline during thermal stratification are shown in FIG. 9. The factors influencing the kinetic process of the dissolved oxygen in the lake and reservoir are numerous, and the factors interact with each other and influence each other. The temperature, dissolved oxygen, biomass, and the material transport rate in the thermocline have large gradients, which makes it extremely difficult to quantify the influence of different processes on the change of dissolved oxygen. The invention researches and develops a construction method of a thermal stratification reservoir thermocline dissolved oxygen prediction model, considers the influence of a plurality of processes such as an algae biological process, an organic matter decomposition process, sediment oxygen consumption and the like on dissolved oxygen, can accurately simulate and predict the formation and development rule of the thermocline dissolved oxygen minimum phenomenon, is beneficial to explaining an oxygen consumption mechanism and predicting future development, is an indispensable tool for researching driving and influencing the change factors of the thermocline dissolved oxygen, and can provide technical support for the ecological environment protection of lakes and reservoirs.

Claims (8)

1. The construction method of the thermal stratification reservoir thermocline dissolved oxygen prediction model is characterized by comprising the following steps of:
s1: acquiring actual measurement terrain data of the thermal stratification lake reservoir to generate a multi-layer Cartesian calculation grid;
s2: obtaining the discretized bottom elevation of each layer of computational grid by adopting a neighborhood method according to the actually measured topographic data;
s3: constructing a three-dimensional hydrodynamic model for simulating the hydrodynamics process of the thermal stratification reservoir based on the bottom elevation according to a continuity equation;
s4: constructing a temperature transport equation according to the thermocline temperature of the thermal stratification reservoir and the solar short wave radiation intensity; constructing a water body surface heat exchange equation according to the surface heat exchange rate and the surface heat coefficient; adopting a temperature transport equation and a water surface heat exchange equation to form a temperature field model;
s5: constructing a mass conservation equation of the water quality variable according to the water quality variable concentration; constructing a dissolved oxygen kinetic equation according to the concentration of the dissolved oxygen, and constructing an eutrophication model by adopting a mass conservation equation of a water quality variable and the dissolved oxygen kinetic equation;
s6: forming a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir by adopting a three-dimensional hydrodynamic model, a temperature field model and an eutrophication model;
s7: acquiring flow information and meteorological conditions of the thermal stratification lake reservoir, and predicting dissolved oxygen of a thermocline of the thermal stratification lake reservoir by adopting a three-dimensional hydrodynamic water quality model of the thermal stratification reservoir;
s8: and judging whether the dissolved oxygen meets the preset condition, if so, a minimum dissolved oxygen region exists in the thermocline of the thermal stratification reservoir, and increasing the dissolved oxygen amount of the thermocline, otherwise, the minimum dissolved oxygen region does not exist in the thermocline of the thermal stratification reservoir.
2. The method for constructing the model for predicting the dissolved oxygen in the thermocline reservoir of the hot stratified reservoir as claimed in claim 1, wherein the continuity equation is as follows:
Figure FDA0003579791610000011
Figure FDA0003579791610000021
wherein ,mx，myAll are coordinate conversion coefficients, and under Cartesian coordinates, the conversion coefficients are equal to 1; zeta is the water surface elevation relative to the reference height in m; h is total water depth, unit m; u, v and w are depth average velocity components in x, y and z directions respectively, and the unit is m/s;
the three-dimensional hydrodynamic model comprises momentum equations in the x direction, the y direction and the z direction, wherein the momentum equation in the x direction is as follows:
Figure FDA0003579791610000022
the momentum equation in the y direction is:
Figure FDA0003579791610000023
the momentum equation in the z direction is:
Figure FDA0003579791610000024
wherein, (x, y) is a curve-orthogonal coordinate in the horizontal direction; z is a vertical sigma coordinate; (u, v) is the horizontal velocity component in the (x, y) direction, in m/s; patmIs atmospheric pressure in Pa; ρ is a reference density ρ0Additional hydrostatic pressure below; b is buoyancy; f is a Coriolis coefficient covering the curvature acceleration of the grid; a. theHIs the horizontal momentum diffusion coefficient, unit m2/s；AvIs the vertical turbulent viscosity coefficient, unit m2/s；CpIs the vegetation resistance coefficient; dpIs a projected vegetation area intersecting the flow per horizontal area; su，SvIs the source and sink term of the momentum equation in the x and y directions respectively, and the unit m2/s2；ShIs the source-sink term of the conservation of mass equation, unit m2/s2(ii) a S is salinity, unit ng/L; t is temperature in units; c is the total suspended inorganic particle concentration in g/m3(ii) a P and Q are mass flux components in the x, y directions, respectively, in m2/s。
3. The method for constructing the prediction model of the dissolved oxygen in the thermocline of the hot stratified reservoir as claimed in claim 2, wherein the calculation formula of the vertical turbulence viscosity coefficient is as follows:
Figure FDA0003579791610000031
wherein ,
Figure FDA0003579791610000032
a stable viscosity coefficient; q is the intensity of the turbulence,unit m2/s2(ii) a l is the turbulent length scale in m;
the calculation formula of the turbulence intensity q and the turbulence length scale l is as follows:
Figure FDA0003579791610000033
Figure FDA0003579791610000034
Figure FDA0003579791610000035
wherein ,SbIs a source and sink item of the turbulence intensity equation; slIs a source and sink item of the turbulent length scale equation; a. theqThe vertical turbulent diffusion coefficient of the turbulent intensity equation; a. theqlThe vertical turbulent diffusion coefficient of the turbulent length scale equation; e1＝1.8，E2＝1.0，E3＝1.8，E4＝1.33，E5＝0.25。
4. The method for constructing the prediction model of the dissolved oxygen in the thermocline reservoir of claim 1, wherein the temperature transport equation is as follows:
Figure FDA0003579791610000041
wherein T is temperature in units; a. thebIs a vertical turbulent diffusion coefficient in m2S; i is the solar short wave radiation intensity and the unit is W/m2；STIs the source and sink term of heat exchange, unit J/s;
the water body surface heat exchange equation is as follows:
Haw＝-Kaw(Ts-Te)
wherein ,HawFor surface heat exchange rate, in W/m2；KawIs the surface thermal coefficient in W/(m)2·℃)；TsIs the water surface temperature in units;
the expression for the light intensity in the water column is:
Figure FDA0003579791610000042
Figure FDA0003579791610000043
Iws＝I0Sfmin{exp[-Ke，me(Hrps-H)]，1}min{exp[-Ke，iceHice]}
wherein ,KeIs extinction coefficient with unit of 1/m; z is the depth below the water surface in m; i iswsIs the light intensity of the water surface, I0Is the intensity of solar radiation on the surface of the earth and has the unit of W/m2；SfIs a shading coefficient; hiceIs the ice thickness in m; k is(e，ice)The extinction coefficient of the ice cover is 1/m; k(e，me)The extinction coefficient of vegetation immersed in water is 1/m; hrpsThe height of the submerged vegetation buds is m.
5. The method for constructing the model for predicting the dissolved oxygen in the thermocline of the hot stratified reservoir as claimed in claim 1, wherein the mass conservation equation of the water quality variables is as follows:
Figure FDA0003579791610000051
wherein C is water quality variable concentration, and the unit is mg/L; a. thex，Ay，AzThe vertical turbulent diffusion coefficients in the x, y and z directions are respectively, and the unit is m2/s；scIs a source and sink item;
the first order kinetic expression is:
Figure FDA0003579791610000052
wherein k is the kinetic rate; r is a source/sink term due to external load and/or internal reaction;
the kinetic equation of dissolved oxygen is:
Figure FDA0003579791610000053
wherein ,CDOIs the dissolved oxygen concentration in g/m3(ii) a c, d, g and m respectively represent blue algae, diatom, green algae and macroalgae; PN (pseudo-noise)xPreference coefficient for class x algae to use ammonia nitrogen, 0 < PNx＜1；FCDxIs a part separated out in the form of dissolved organic carbon in the basic metabolism of the x-class algae;
Figure FDA0003579791610000065
is dissolved oxygen half-saturation constant, g/m, excreted by organic carbon in the dissolved state of algae of the x class3(ii) a AOCR is the oxygen consumption of organic carbon in respiration, and the value is 2.67; AONT is ammonia nitrogen nitration oxygen consumption per unit mass, and the value is 4.33; nit is the nitration rate, and the unit is 1/d; kHRThe unit is 1/d of the abnormal respiration rate of the dissolved organic carbon; cDOCIs the concentration of dissolved organic carbon in g/m3；KHCODIs the oxygen half-saturation constant in g/m3；KCODThe oxidation rate of COD is 1/d; cCODIs chemical oxygen demand concentration in g/m3；KRIs the reoxygenation coefficient with the unit of 1/d; cDOSIs saturated dissolved oxygen concentration in g/m3(ii) a SOD is sediment oxygen demand with the unit of g/(m)2·d)；WDOIs the external load in g/d.
6. The method for constructing the thermal stratification reservoir thermocline dissolved oxygen prediction model according to claim 1, wherein the preset conditions are as follows:
C1(z，t1)＝C0(z，t0)+ΔC(z，Δt)
Figure FDA0003579791610000061
Figure FDA0003579791610000062
Figure FDA0003579791610000063
Figure FDA0003579791610000064
wherein ,C1Is t1The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; c0Is t0The concentration of dissolved oxygen at the water depth z at the moment is unit mg/L; Δ C is the time interval (t) of Δ t1-t0) The concentration of dissolved oxygen at the inner water depth z is changed, and the unit mg/L is; MOM is the minimum value of dissolved oxygen in the thermocline.
7. The method for constructing the model for predicting dissolved oxygen in a thermocline of a hot stratified reservoir as claimed in claim 1, wherein in step S1, the cartesian calculation grid includes a plurality of horizontal rectangular grids, and the plurality of horizontal rectangular grids adopt SGZ coordinates in the vertical direction; the interval between two adjacent layers of horizontal rectangular grids is 1.5m-2.5 m.
8. The method for constructing the thermal stratification reservoir thermocline dissolved oxygen prediction model according to claim 1, wherein in step S3, the boundary conditions of the three-dimensional hydrodynamic model include upstream flow, downstream flow and meteorological conditions, wherein the meteorological conditions are atmospheric pressure, air temperature, relative humidity, rainfall, evaporation, solar radiation, cloud shielding coefficient, wind speed and wind direction.
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