CN108287950B

CN108287950B - Water quality simulation method based on water environment quality target management of control unit

Info

Publication number: CN108287950B
Application number: CN201711497530.1A
Authority: CN
Inventors: 陈岩; 白辉; 赵琰鑫; 王东; 吴悦颖; 韦大明; 赵康平; 孙运海
Original assignee: Environmental Planning Institute Of Ministry Of Ecology And Environment
Current assignee: Environmental Planning Institute Of Ministry Of Ecology And Environment
Priority date: 2017-12-27
Filing date: 2017-12-27
Publication date: 2021-09-14
Anticipated expiration: 2037-12-27
Also published as: CN108287950A

Abstract

The invention provides a water quality simulation method based on water environment quality target management of a control unit, which comprises the following steps: establishing a database; dividing a land area control unit and a river channel subunit; simulating and calculating the flow, the water surface area and the water volume of the unit grid by adopting a hydraulics model; calculating the non-point source pollutant generation amount in the pollution source by adopting an output coefficient model, and calculating the river sewage amount and the pollution load concentration of the pollutants at the sewage outlet; simulating the water quality of the grid of the computing unit by adopting a one-dimensional water quality model; the simulation method also adopts a sudden risk accident pollution discharge water quality model to simulate the transmission of accident pollutants in a river network and the change condition of the water quality of a downstream drainage basin after sudden water environment risk accident pollution discharge.

Description

Water quality simulation method based on water environment quality target management of control unit

Technical Field

The invention belongs to the field of water environment monitoring, management and protection, and particularly relates to a water quality simulation method based on water environment quality target management of a control unit.

Background

The control unit in the water environment planning and management is a drainage basin divided region serving as a unit, and provides control measures for the emission concentration and the total amount of pollution in the unit, so that the aim of recovering and maintaining the water environment quality of the drainage basin is fulfilled finally. The water quality target management based on the control unit is a water environment capacity total amount control technology.

The establishment of the watershed water quality model is a key technical point for realizing the control unit water quality target management, and the establishment of the input response relation between pollutant emission and water quality by selecting a proper water quality model can describe the migration and transformation rules of pollutants in the watershed range along with time and space, study the influence factors of the pollutants, and predict the water environment development trend on the basis of scientific parameter calibration. The watershed water environment model can be used for water environment simulation and evaluation, water quality prediction and prediction, auxiliary pollutant emission standard establishment, water quality planning, auxiliary water area water quality management and the like, and is an important tool for watershed water environment planning, management and research. After decades of development, the model technology has become an important tool for water environment management in developed countries abroad. On the one hand, it is expressed in the number of models: so far, more than 60 pieces of watershed water environment model software published by the ministry of research and development of the national environmental protection agency of the United states are widely applied to watershed pollutant generation and migration processes, water environment process simulation, morphological distribution calculation, aquatic organism growth, ecological effect simulation and the like; on the other hand, it is expressed on the scale of the model: the basin water environment model is continuously developed and perfected from a simple, isolated and dispersed hydrological model, a non-point source model and a water quality model, different sub-modules in the model and mutual permeation and coupling combination between the model and other related models gradually develop into a basin comprehensive water environment management model taking basin water quality management as a core. The popularization and application of basin composite model systems such as BASINS, EPA TMDL Toolbox and WMS become representative results in the direction.

In order to better apply the model in watershed water environment management and planning, the united states environmental protection agency performs post-evaluation on 65 models widely used in the TMDLs plan in 2005, and indicates that a suitable model is selected for actual characteristics and demand targets, which is the basis and premise for realizing application of model technology to management decision support. The modeling research of the environmental management in China starts late, and in recent years, although foreign models such as SWAT, MIKE BASIN, SPARROW and the like are applied in experiments in part of the watershed of China, the model is seriously limited to be popularized and applied due to various problems that the model needs to be operated by professional technicians, basic data is difficult to obtain, the model verification lacks method standards and the like, and the modeling method is far from being suitable for the actual requirements of scientific, standardized and standardized work such as environmental planning, management and the like.

Disclosure of Invention

The invention solves the technical problems that basic data are difficult to obtain and model verification lacks method standards in a water quality simulation model in the prior art, and further provides a water quality simulation method which is simple and convenient to operate, can make up for the deficiency of the basic data and can effectively verify and is suitable for water environment quality target management based on a control unit.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a water quality simulation method based on water environment quality target management of a control unit comprises the following steps:

(1) establishing a database, comprising: the drainage basin geographic information database is used for recording the geographic information data of the drainage basin; the hydrological, meteorological and water quality monitoring database is used for recording hydrological and water quality data in a flow domain and meteorological monitoring data corresponding to the meteorological station; the drainage basin environmental statistics database is used for collecting the emission data of various pollution sources of the drainage basin, and the social and economic and demographic information data of the drainage basin; the model parameter database is used for recording the pollution discharge coefficient of a typical pollution source, the river entering coefficient of the pollution source, the conventional pollutant transmission-degradation coefficient and the toxic and harmful substance transmission-degradation coefficient; (2) preliminarily dividing the river into a plurality of non-uniform river sections, dividing each river section into a plurality of sub-computing units, and finally determining sub-computing unit grids of the whole watershed water system; (3) calculating the non-point source pollutant production amount by adopting a drainage basin non-point source pollution discharge model, wherein the non-point source pollution discharge characteristic in each control unit is analyzed, the data in a drainage basin environment statistical database, a drainage basin geographic information database, a hydrological, meteorological and water quality monitoring database and a model parameter database are extracted, and the non-point source pollutant production amount in a pollution source is calculated by adopting a drainage basin non-point source pollution discharge coefficient model; the non-point sources comprise urban living sources, livestock breeding sources, planting industry surface sources, rural living surface sources and urban non-point sources; (4) determining the hydrological conditions of the river reach by adopting a hydrological calculation method; analyzing hydrological meteorological characteristics of the river reach, analyzing the availability of hydrological data, and selecting an applicable hydrological interpolation method: if hydrologic monitoring sites are arranged at the upstream and the downstream of the existing river reach, extracting flow data in the hydrologic, meteorological and water quality monitoring databases, and calculating the flow of the river reach by adopting a natural runoff reduction method; when the river reach lacks upstream and downstream hydrological monitoring sites, hydrological data of the drainage basin can be extracted, the river reach with basically the same hydrological conditions is found, and the flow of the river reach is estimated by adopting a hydrological comparison method; further calculating the water surface area and the water volume of the river reach based on the flow; (5) based on the calculated data in the steps (3) and (4), simulating the water quality of the sub-calculating unit by adopting a watershed one-dimensional river network hydrodynamic water quality model method, wherein the method comprises the following steps: the method comprises the following steps of firstly, extracting position information of a pollution source, a sewage outlet and a water intake in a drainage basin geographic information database, and generalizing adjacent sewage outlets in the same sub-computing unit; extracting various point source discharge data in the drainage basin environment statistical database and the calculation result in the step (3), and further calculating the river inflow sewage quantity and the pollution load concentration of the pollutants at the sewage discharge outlet after generalization according to the river inflow coefficient in the model parameter database; calculating the flow speed condition of the river reach by adopting a river water dynamic model method according to the calculation result of the step (4); secondly, verifying and calibrating the one-dimensional water quality model by adopting independent data, so that the simulation precision of the one-dimensional water quality model is not lower than 80%; and calculating the grid pollution load concentration of each calculation unit by adopting the verified and calibrated water quality model.

The geographical information data of the drainage basin recorded by the drainage basin geographical information database comprises land area ranges, administrative divisions, river systems, landforms, hydrological and meteorological sites, water quality monitoring sections and position information of various pollution sources, sewage outlets and water inlets.

In the step (5), the method further comprises the following steps: and extracting the degradation coefficient in the conventional pollutant transmission or toxic and harmful substance transmission-degradation coefficient database in the model parameter database by using the river one-dimensional sudden risk accident simulation model, and simulating the change condition of the water quality of the downstream drainage basin after sudden water environment risk accidents are discharged.

The river water dynamic model method comprises a river water level-flow relation method and a Manning formula method; the watershed one-dimensional river network hydrodynamic water quality model method comprises a river constant pollution discharge one-dimensional steady-state water quality degradation model.

In the step (5), when the sewage outlets are generalized, for the sewage outlet of the point source, a plurality of adjacent sewage outlets in the same sub-computing unit grid can be generalized into a centralized sewage outlet; the method for calculating the river sewage amount and the pollution load concentration of the pollutants at the sewage outlet comprises the following steps: 1) determining the corresponding relation between the sewage draining exit and the pollution source; 2) calculating the sink-in distance from the pollution source to the sewage outlet; 3) determining river entering coefficients according to the river entering distance; 4) and accumulating all pollution sources of each sewage discharge outlet to obtain the river sewage amount and the pollution load concentration of the sewage discharge outlet.

And regarding the sewage discharge outlets of the non-point sources, generalizing the sewage discharge outlets into line discharge outlets along the course of the river reach, taking the point positions of the starting point and the end point of each non-point source influence river reach as boundary lines, and averagely distributing the load of the pollution source to each influenced sub-computing unit grid in the range.

In the step (2), river reach with basically the same water power, water quality characteristic and parameter value are divided into the same river reach, and the water power and/or water quality characteristic of each river reach are different; the sub-calculation units are the minimum units for water quality simulation, and each river reach is composed of an integral number of sub-calculation units.

And respectively coding the divided river reach and the sub-computing units to clarify connection and sink topology relations among river networks.

Dividing the river reach with basically same water power, water quality characteristics and parameter values into the same river reach, and then further dividing the river reach with a sensitive point into an upstream independent river reach and a downstream independent river reach at the sensitive point, wherein the sensitive point comprises any one of the following positions: the control unit divides a boundary; water environment function partitioning; the junction of the river stem and the branch; a water quality monitoring station; where the hydraulic characteristics are changed significantly, wherein the hydraulic characteristics refer to any one of flow speed, water depth and river width; at the tidal river reach boundary.

Dividing all the sub-computational unit grids into: the source head water unit grid is source head water of a drainage basin; the tributaries are imported into the sink unit grids, and non-source water unit grids into which the tributaries are imported; common unit grids without non-source water unit grids for branch flow import; for the source water unit grid, a sink is arranged in the middle of the source water unit grid; and for the tributary import and export unit grid, the tributaries are gathered to be imported at the upstream start position of the tributary import and export unit grid, and the drain outlet is gathered to be the position where the tributary import and export unit grid is placed in the middle.

In the invention, on the basis of defining the scope of the drainage basin, a land area control unit and a river channel unit are divided. The land unit division considers river catchment characteristics and administrative boundaries and divides the river basin into a series of control units. On the basis, in the step (2), river catchment characteristics and administrative boundaries of the drainage basin are considered, the drainage basin is divided step by step from top to bottom, and the drainage basin is adjusted layer by layer from bottom to top, and the drainage basin and the land are sequentially divided into a series of control areas, control units and control subunits, so that differences of production sewage and water environment quality caused by space difference characteristics of natural conditions and social and economic conditions of the drainage basin are reflected. The control unit is the most basic unit for carrying out water environment quality target management. The river channel data is organized by river reach and is associated with the land area control unit, the river reach with basically the same waterpower, water quality characteristics and parameter values is divided into the same river reach, and the waterpower and/or water quality characteristics of each river reach are different; the sub-calculation units are the minimum units for water quality simulation, and each river reach is composed of an integral number of sub-calculation units. The generalized river channel subunits do not need to be strictly equal in length, but the generalized sub-computing unit river network is basically consistent with the actual river water body in the aspects of water delivery capacity, regulation capacity and the like.

In practical application, the river reach and the computing unit are analyzed and coded and sorted according to topological relation. And respectively coding the divided river reach and the calculation unit to clarify the connection and sink topology relation between the river networks. For a standard river network, the main steps of encoding the river reach and the computing unit comprise: 1) determining a main river according to the principle that the water collection area is large, and numbering main stream river sections from upstream to downstream in an ascending order from 1 by taking the source of the main river as a starting point; 2) when a river channel is forked, namely a branch is converged, pausing numbering and recording a current number value N, tracing to a branch source along a branch which is converged, numbering the branch source as N +1, numbering branch river reach in sequence from upstream to downstream along the branch until the branch enters a trunk inflow convergence port, and recording a current number value M; 3) relocating the current coding river reach to the main stream, and sequentially numbering the main stream river reach below the inlet junction from the upstream to the downstream from M + 1; 4) repeating the above processes until reaching the river basin outlet, and finishing the river reach coding; 5) and traversing the river reach in sequence according to the codes, and coding the divided computing units of each river reach in sequence from the upstream to the downstream to finally form ascending numbers of the continuous river reach from the main stream source to the drainage basin outlet and the computing units.

The water quality simulation method based on the water environment quality target management of the control unit adopts a model integrating a drainage basin non-point source product pollution discharge coefficient model, a hydrological interpolation calculation method, a river water power model method, a river one-dimensional water quality model method and the like. Wherein, the river water dynamic model method comprises a river water level-flow relation method and a Manning formula method; the river one-dimensional water quality model method comprises a river constant pollution discharge one-dimensional steady-state water quality degradation model, a river one-dimensional sudden risk accident simulation model and other various model methods, and specifically comprises the following steps:

non-point source production pollution discharge coefficient model method

The pollutant output coefficient is a standardized estimation of the total pollutant load output in a certain land utilization mode in unit time, and is mostly expressed by the load quantity of unit area in unit time. The output coefficient method is used for estimating the non-point source pollution load output by the drainage basin by utilizing the pollutant output coefficient, and is a lumped simple and convenient non-point source pollution load estimation method. The output coefficient model is a concrete embodiment of an output coefficient method, is a mathematical weighting formula for calculating annual average pollution such as total nitrogen and total phosphorus load on a watershed scale by using a semi-distributed approach, and is a semi-distributed lumped model in essence. Because the source pollution load of the drainage basin is closely related to the land utilization type in the drainage basin, the relationship between the drainage basin land utilization type and the non-point source pollution output quantity is directly established by utilizing data such as the drainage basin land utilization type which is relatively easy to obtain through multivariate linear correlation analysis, and then the total non-point source pollution load of the area is obtained by summing the pollution loads from different sources.

1. Livestock and poultry breeding source

The non-point source pollution load calculation of the livestock and poultry breeding industry is shown as the following formula:

Q＝∑A_i*T_i*E_j

in the formula: q is non-point source pollution load discharge amount of livestock and poultry breeding industry, ton/year, A_iThe number of breeding stocks for the breeding species of the i-type livestock and poultry is the number of the breeding stocks (only); t is_iThe coefficient of the dirt production of the i-type livestock and poultry breeding is gram/day; e_jThe treatment efficiency of j breeding manure treatment modes is improved.

Considering the stock keeping amount of cattle, pigs, sheep and poultry as a relatively stable feeding amount in the current year according to the estimation method of related research, and on the premise of not considering the feeding period, the livestock and poultry breeding pollutant production coefficient (T)_i) The calculation formula is as follows:

production of livestock and poultry pollutants (T)_i) Daily excretion coefficient of livestock and poultry manure (kg/head-year) x pollutant content of manure (g/kg).

2. Non-point source for planting industry

And estimating the non-point source loss of the planting industry by adopting a standard farmland method. The standard farmland refers to a farmland with plain, wheat as a planted crop, loam as a soil type, 25-35 kg/(mu-year) of fertilizer application amount and 400-800mm of precipitation amount.

For an actual farmland, factors such as an actual gradient, crop planting types, soil properties, fertilizer application amount, precipitation distribution and the like need to be considered, and on the basis of a standard farmland, a source intensity coefficient is corrected necessarily:

A. slope correction (a)_{Slope correction})

The land gradient is below 25 degrees, and the loss coefficient is 1.0-1.2; over 25 degrees, and the loss coefficient is 1.2-1.5. And analyzing the average gradient of the cultivated land by using the drainage basin geographic information database, and determining a corresponding correction factor.

B. Crop type correction (b)_{Crop type correction})

The method is characterized in that main crops such as corn, sorghum, wheat, barley, rice, soybean, cotton, oil plants, sugar materials, economic forests and the like are used as research objects, and the pollutant loss correction coefficients of different crops are determined.

C. Soil type correction (c)_{Soil type correction})

Farmland soil is classified according to texture, namely according to the proportion of clay to sandy soil in soil components, the soil is classified into sandy soil, loam and clay. Taking loam as 1.0; the sand correction coefficient is 1.0-0.8; the clay correction coefficient is 0.8-0.6. And taking 0.9-1.0 according to the soil type of the drainage basin.

D. Correction of fertilizer application amount (d)_{Chemical fertilizer application amount correction})

The application amount of the fertilizer per mu is below 25kg, and the correction coefficient is 0.8-1.0; the correction coefficient is 1.0-1.2 between 25-35; above 35kg, the correction coefficient is 1.2-1.5.

E. Precipitation correction (e)_{Precipitation correction})

The annual rainfall is below 400mm, and the loss coefficient is 0.6-1.0; taking the loss coefficient to be 1.0-1.2 in areas with annual rainfall between 400 and 800 mm; the annual rainfall in the area with the annual rainfall above 800mm is taken to have the loss coefficient of 1.2-1.5. The average annual precipitation of the drainage basin is 600-300mm, and the precipitation correction factor is determined according to the annual precipitation map and the farmland distribution map of the drainage basin.

The formula of the load discharge amount of the planting industry is as follows:

in the formula, E_PlantingThe discharge amount of the load is ton/year for the drainage basin planting industry; e_{Standard farmland}The loss coefficient is the loss coefficient of the planting mode of the 'standard farmland' in the drainage basin, namely kilogram/mu.year; a. the_{Planting Pattern i}Adopting planting area of i-th planting mode for the drainage basin, mu; a is_{Slope correction}The gradient correction factor is a non-dimensional gradient correction factor; b_{Crop type correction}The crop type is corrected, and the method is dimensionless; c. C_{Soil type correction}The soil type correction is carried out, and the dimension is not needed; d_{Chemical fertilizer application amount correction}The fertilizer application amount is corrected, and no dimension is needed; e.g. of the type_{Precipitation correction}The method is dimensionless for correcting the precipitation.

3. Rural life non-point source

The rural life pollution discharge condition is determined according to the pollution load discharge of rural population and average rural population of each control unit, and is shown as the following formula:

W＝3.65AF

in the formula, W is the rural area source load discharge amount, ton/year; a is rural population, ten thousand people; f is the coefficient of pollution discharge of rural residents, g/(man-day).

4. City non-point source

And estimating the runoff surface source runoff loss of the city by adopting a standard city pollution discharge coefficient method. The definition of so-called "standard city" is: is located in plain zone, the urban non-agricultural population is between 100 and 200 thousands, and the area of the built-up area is 100km²And on the left and right, the annual precipitation is between 400 and 800mm, the popularity of the urban rainwater collection pipe network is between 50 and 70 percent, and the standard urban source intensity coefficient is COD 50 tons/year and ammonia nitrogen 12 tons/year.

The method considers a plurality of factors influencing urban runoff, and further performs coefficient correction on the basis of a standard city by comparing specific conditions such as planned evaluation of urban built-up area topographic features, urban population, urban area, rainfall, pipe network coverage and the like:

A. terrain correction factor (T)_City)

The city is divided into 3 conditions of plain city, mountain city and hill city according to terrain, and terrain correction coefficients are respectively given. Wherein, the landform correction coefficient of the plain city is 1; the correction coefficient of the mountain city is 3.8; and the correction coefficient of the hill city is 2.5.

B. Population correction factor (P)_City)

Population correction coefficients are respectively given for 4 cases of urban non-agricultural population of less than 100 ten thousand, 100 ten thousand to 200 ten thousand, 200 ten thousand to 500 ten thousand and more than 500 ten thousand. Wherein, the population correction coefficient is 0.3 for less than 100 ten thousand persons; the correction coefficient is 1 between 100 ten thousand and 200 ten thousand; the correction coefficient is 2.3 between 200 and 500 ten thousand; more than 500 ten thousand correction coefficients are taken as 3.3.

C. Area correction factor (A)_City)

The area integral of the built city is 75km²75-150 km below²、150～250km²、250km²In the above 4 cases, the area correction coefficients are given separately. Wherein, 75km²The area correction factor is taken as 0.5; 75-150 km²Taking a correction coefficient as 1; 150 to 250km²Taking the correction coefficient to be 1.6; 250km²The correction factor was taken to be 2.3.

D. Rainfall correction factor (R)_City)

And (3) respectively giving rainfall correction coefficients for the annual rainfall under 400mm, 400-800mm and over 800 mm. Wherein the rainfall correction coefficient is 0.7 when the rainfall correction coefficient is less than 400 mm; taking a correction coefficient of 1 between 400 and 800 mm; the correction coefficient is 1.4 when the thickness is more than 800 mm.

E. Pipe network correction factor (P)_{n city})

The coverage rate of the rainwater collection pipe network is divided into 4 conditions of less than 30%, 30-50%, 50-70% and more than 70%, and pipe network correction coefficients are respectively given. Wherein, the rainwater collection pipe network coverage rate is below 30%, and the pipe network correction coefficient is 0.6; taking the correction coefficient of 0.8 when the coverage rate is between 30 and 50 percent; taking a correction coefficient of 1 when the coverage rate is 50-70%; the correction coefficient for a coverage of 70% or more was 1.2.

The urban non-point source accounting formula is as follows:

E_city＝E_{Standard city}×T_City×P_City×A_City×R_City×P_{n city}

In the formula, E_CityThe discharge amount of urban runoff non-point source load is ton/year; e_{Standard city}The standard urban runoff load emission intensity defined in the flow field is ton/year; t is an urban terrain correction coefficient and is dimensionless; n is a radical of_CityThe urban population correction coefficient is dimensionless; a. the_CityThe urban area correction coefficient is dimensionless; r_CityThe correction coefficient is a correction coefficient of the urban precipitation, and is dimensionless; p_{n city}The correction coefficient is a correction coefficient of the urban rainwater pipe network and is dimensionless.

Hydrological interpolation calculation method

For a certain river reach sub-calculation unit, if an actual hydrologic monitoring site is located on a river reach of a water environment functional area (water functional area) to which the river reach sub-calculation unit belongs, the actual measurement flow value of the hydrologic monitoring site is directly adopted as the incoming flow condition of the river reach. In consideration of the uneven characteristic of the distribution of the actual hydrologic monitoring sites, many river reaches actually do not measure hydrologic data. For the river reach sub-calculation unit, if there is no actual hydrologic monitoring site on the river reach of the water environment functional area (water functional area) to which the river reach sub-calculation unit belongs, the original hydrologic data needs to be preprocessed according to the production convergence relation in the flow domain, and the original hydrologic data is interpolated and restored to other river reach without actual measured hydrologic data.

1. Interpolation method

When hydrologic stations are arranged at the upstream and downstream of the river reach of the water environment functional area (water functional area) to which a certain sub-computing unit belongs, actual flow observation data (Q) of the current month of the upstream and downstream stations can be used^{On the upper part}、Q^{Lower part}) The average flow of the river reach of the water environment functional area (water functional area) is estimated by an interpolation method, and the calculation formula is as follows:

wherein Q is the result of accounting the flow of a river section lacking hydrologic monitoring data, m³/s；Q^{On the upper part}、Q^{Lower part}Measured in a month at upstream and downstream hydrological stations, respectivelyFlow rate, m³S; a is the average water yield of the river basin above the control section of the data station for many years, m³；A^{On the upper part}、A^{Lower part}Average water yield m in many years in the watershed controlled by upstream and downstream hydrological stations respectively³。

2. Hydrological comparison method

For non-data areas, hydrological analogy (analogy) methods may also be used. Firstly, finding out a drainage basin which is similar to the climate lacking the data drainage basin and the natural geographic condition, has little difference in drainage basin area and has longer-term actual measurement data as a reference (analog) drainage basin, and transferring the statistical parameters of the runoff quantity or the runoff process of the reference drainage basin time period to the data-lacking drainage basin after correction, wherein the calculation formula is as follows:

river water power model method

1. Equation of water balance

The river reach unit water quantity balance equation is as follows:

Q_i＝Q_i-1+Q_in,i-Q_out,i

in the formula, Q_iFlow rate of river reach i into river reach i +1, m³/s；Q_i-1Is the flow rate of the upstream river reach i-1 flowing into the river reach i, m³/s；Q_in,iI point source and non-point source total inflow of the river reach m³/s；Q_out,iI point source and non-point source total output flow of river reach m³/s。

All incoming flows from the source can be expressed as:

wherein Q is_ps,i,jIs the flow of the j point source into the river reach i, m³Psi is the number of all point sources in the river reach i, Q_nps,i,jIs the flow of the jth non-point source flowing into the river section i, m³D, npsi is all non-points of river section iThe number of sources.

All the outgoing flow from the source can be expressed as:

wherein Q is_pa,i,jIs the flow of the source intake at the jth point of the river reach i, m³The number of water intakes of all point sources of the river reach i is/d, pai, Q_npa,i,jIs the flow of the jth non-point source water intake of the river reach i, m³And/d, npai is the number of all non-point source water intake ports of the river reach i.

2. Water level-flow relation equation

The concrete idea of adopting the water level flow relation curve method to estimate the average flow speed condition according to the flow is that the relation between the flow speed and the flow and the relation between the depth and the flow in the river reach unit can be described by a power exponent equation:

U＝aQ^b

H＝cQ^d

wherein Q is the flow rate, m³S; u is the average flow velocity, m/s; h is the average water depth, m; a. b, c and d are empirical constants and can be obtained by calculating intercept and slope of a water level-flow relation curve of a cross section. From the flow velocity and depth calculations, the cross-sectional flow area and average river width can be further determined by the following equations:

3. manning formula method

Assuming that each river reach is a trapezoidal channel, the flow is calculated by using the Manning formula as follows:

wherein p is the wet week; n is a Manning roughness coefficient; s₀Is slope,%; a. the_cIs the flow area.

For a trapezoidal channel, the formula for calculating the flow area is as follows:

A_c＝[B₀+0.5(S_S1+S_S2)H]H

the wet cycle calculation formula is:

the formula for calculating the depth of the section water is as follows:

wherein, B₀Is the width of the bottom of the river channel, m; s_S1、S_S2Is the slope gradient of the side slopes on two sides of the river channel.

One-dimensional water quality model method for river channel

The model is suitable for the dendritic river, allows the discharge of waste water from a plurality of point sources along the river, the entrance of a surface source into a sink, the taking of water and the inflow of branches to analyze the influence of the total discharge amount and the specific discharge position of pollutants on the water quality of a received water body, and can be used as a steady-state model or a time-varying dynamic model to simulate sudden water environment pollution accidents and the like.

1. Constant-pollution-discharge one-dimensional steady-state water quality degradation model

For the water quality change caused by the point source and non-point source pollution discharge of each sub-calculation unit of the river, a constant pollution discharge one-dimensional steady state degradation water quality model is adopted for simulation analysis:

wherein C (x) is the concentration of contaminant at river x, mg/L; c₀The concentration of the initial section of the river sewage outlet is mg/L; x is the length of the river, m, x is 0 at the sewage discharge outlet, x>0 denotes the downstream side of the sewage discharge outlet, x<0 refers to the upstream side of the sewage draining exit; u is the cross-sectional flow velocity, m/s; k is the comprehensive attenuation coefficient of pollutants, 1/s; c_pThe concentration is the pollutant emission concentration, mg/L; q_pM is the discharge amount of sewage³/s；C_hThe concentration of the river pollutants is mg/L; q_hIs the flow rate of river, m³/s；D_xIs the longitudinal dispersion coefficient of the contaminant, m²/s。

For the case that the change of the cross section flow velocity of the small river is not large, the simplified form of the formula is as follows:

C₀＝(C_pQ_p+C_hQ_h)/(Q_p+Q_h)

for the degradation coefficient k in the formula, the national water environment capacity accounting general recommended value: the COD degradation coefficient is generally not more than 0.2d^-1The degradation coefficient of ammonia nitrogen is generally not more than 0.15d^-1. The value of the pollutant degradation coefficient in the watershed water environment capacity calculation can be comprehensively considered and determined in the range, and under the normal condition, the value range of the COD degradation coefficient is 0.2-0.3 d^-1(ii) a The value range of the ammonia nitrogen degradation coefficient is 0.10-0.2 d^-1. Because the degradation coefficient changes greatly along with the temperature, in the actual water quality model calculation, the COD and ammonia nitrogen degradation coefficients are corrected according to the average water temperature of each monthly basin, and the formula is as follows:

DK_Temp＝DK_20℃*1.047(^Temp-20℃)

in the formula (II) DK_TempUnder the condition of actual water temperature in a certain monthCoefficient of degradation, DK_20℃The degradation coefficient is 20 ℃, and Temp is the actual water temperature in a month.

2. Sudden risk accident pollution discharge water quality model

After the sudden water environment risk accident pollution discharge process, the accident pollution discharge influences the water quality change of the stem and branch of the river, and for degradable pollutants, such as COD, ammonia nitrogen and other conventional pollutants, degradable toxic and harmful organic pollutants, acid and alkali and the like, the formula is as follows:

in the formula, C_bThe background concentration value of the river accident pollutant is mg/l; c (x, t) is x from the occurrence risk accident, and the pollutant concentration at the t moment after the accident occurs is mg/L; x is the distance from the sewage outlet, m; u is the cross-sectional flow velocity, m/s; k is the comprehensive attenuation coefficient of pollutants discharged by the risk accident, 1/s; (ii) a D_xIs the longitudinal dispersion coefficient of the contaminant, m²S; m is the quality of one-time emission of the sudden water environment risk accident pollutants, g

For refractory contaminants, the formula is as follows:

fifth, sewage draining outlet generalization method

The sewage draining exit solves the water-land coupling problem between the pollution source and the river water system. Point source and non-point source pollution loads must be distributed to the corresponding waste outlets. While the model allows a single drain to correspond to virtually any number of point or non-point sources of pollution.

1. Point source

The point source determines the sub-calculation unit grid to which the point source belongs according to the actual position of the point source, a plurality of adjacent point source sewage outlets or water intakes can be simplified into a concentrated sewage outlet or water intake, and the distance between the combined sewage outlet and the upstream section can be calculated by the following formula:

in the formula, L is the distance (km) from the generalized sewage discharge outlet to a control section at the upstream of the river reach; q_iThe amount of water (m) of the ith sewage outlet³/s)：C_iThe pollutant concentration (mg/L) of the ith sewage outlet; l is_iThe distance (km) from the ith sewage draining exit to the upstream control section of the river reach is shown.

2. Non-point source

The non-point source sewage draining exit or water intake is generalized to be a line draining source or a line water intake along the river reach. The model takes the point positions of the initial point and the terminal point of each non-point source influence river reach as boundary lines, and the non-point sources are evenly distributed to each unit according to the distance in the area to calculate the water quality.

3. Pollution source and sewage draining outlet association method

The pollution source and the sewage draining outlet are associated and treated by the following steps: 1) firstly, establishing a drain outlet-pollution source attribute table, and determining the relation between a drain outlet (water) and a pollution source (land); 2) calculating the sink entering distance from the point source to the sewage outlet; 3) determining river entering coefficients according to the river entering distance; 4) and accumulating all pollution sources of a certain sewage discharge outlet to obtain the river sewage amount and the pollution load concentration of the sewage discharge outlet.

The water quality simulation method provided by the invention comprises the following steps that 1) from the aspect of a model algorithm, aiming at data conditions and application requirements, the simulation requirements of the development of the social economy of the drainage basin, the production of sewage and the response analysis of water quality are fully met through a model specification and model solidification method; 2) from the aspect of parameter data, aiming at the current situations that relevant early-stage research foundations of a considerable part of places are weak and data accumulation is less, model recommendation parameters which comprehensively reflect the local socioeconomic characteristics and the drainage basin characteristics are directly collected and sorted based on a production and pollution discharge accounting manual, a capacity and water quality accounting guide rule and the like; 3) in the aspect of model application, a watershed-control area-control unit partition and water environment functional area (water functional area) partition system is comprehensively considered.

In order to make the technical scheme of the water quality simulation method based on the water environment quality target management of the control unit more clearly understood, the invention is further described in detail below with reference to the specific drawings and specific examples.

Drawings

FIG. 1 is a diagram of a model system of the water quality simulation method according to the present invention;

Detailed Description

The embodiment further describes the water quality simulation method in the present invention, which takes the Qinghai watershed as an example, and a model system diagram of the water quality simulation method adopted in the embodiment is shown in fig. 1.

First, a database is established for the simulation of water quality of a water basin, wherein the database comprises: a pollution source product pollution discharge information database which records pollution source information, sewage outlet information, water intake information and river entering coefficient; a drainage basin geographic information database; the hydrologic water quality monitoring database is used for recording hydrologic data of a drainage basin and water quality data monitored by a monitoring station, and the data are dynamically updated according to a detection result; a conventional pollutant transmission-degradation coefficient database and a toxic and harmful substance transmission-degradation coefficient database.

10 branch river water bodies in a water basin are divided into 158 water environment functional areas, wherein 14 lake and reservoir functional areas are provided, and the total area of the lake and reservoir is 15.4km²(ii) a The river type functional areas are 144, and the total length of the river channel is 2451.7 km. 5 industrial water areas are provided, and the length of a river channel is 47.4 km; the number of source head water protection areas is 6, and the length of a river channel is 163.4 km; 63 water areas for landscape entertainment are provided, which relate to the length of a river channel of 1015.1km and the area of a lake reservoir of 3.1km²(ii) a 84 drinking water source protection areas are provided, which relate to the length of a river channel of 1235.8km and the area of a lake reservoir of 12.3km²。

According to the zoning achievement of the water environment function of the lunge watershed, the research preliminarily divides 56 main dry-tributary rivers in the lunge watershed into 134 non-uniform river sections according to the zoning situation of the water environment function, the same river section has the same characteristics of hydraulic power and water quality parameters such as specific drop, flow speed and pollutant degradation coefficient, and the hydraulic power and water quality characteristics of the river sections are different. On the basis, dividing 134 river reach into sub-computing unit grids with basically equal length to form sub-computing unit grids with basically 1000 m; then, traversing all the river reach, and seeing whether there is a water quality monitoring section and a water environment functional area node on the river reach, and breaking the river reach at the section position, and finally dividing the whole moisture river basin into 2820 sub-computing unit grids. The sub-calculation unit grid is a basic unit for water quality simulation analysis and calculation. Non-point sources and the in-out and out-flow of point sources may be within any river segment or grid of sub-computing units.

For each computing unit grid divided in the moisture domain, starting from the upstream bast temple river source on the water of the 10, numbering in an ascending order from 1 to downstream, and continuing to numbering in an ascending order from the tributary source to the tributary downstream when arriving at a tributary, thereby generalizing all dry tributaries in the whole moisture domain into a series of sub-computing unit grids connected end to end.

The last determined minimum numbering (No. 1) unit of the river network computing unit in the watershed is located at the 10 upstream 10 fair source hempsey river source, and the maximum numbering (No. 2719) unit is located at the exit of the watershed. The sub-calculation units of the two branches of the salt water ditch and the Longzhi ditch are numbered from 2720 to 2820, and the two branches are individually numbered.

Each tributary of the water basin has 16 main hydrological monitoring sites. Wherein, the major hydrological stations on the water trunk flow include 5 kayan three stations, a source station, a xining station, a ledu station, a min station, and a station, among other branches, the major hydrological stations on the north river include 3 cow stations, five bridgehead stations, and a yang facing station, the major hydrological stations on the liquid medicine river include 1 hollander three station, the west river includes 1 hollander two station, the black river includes 1 black river 1 hydrological station, the south river includes 1 kawa estuary station, the shatang river includes 1 kazai two station, the little south river includes 1 queensland station, the attraction ditch includes 1 irie bridge three station, and the baoba river includes 1 kamikazakh station.

In this study, for a certain river reach sub-calculation unit, if an actual hydrologic monitoring site is located on a river reach of a water environment functional area to which the river reach sub-calculation unit belongs, the actual measurement flow value of the hydrologic monitoring site is directly used as the incoming flow condition of the river reach. In consideration of the uneven characteristic of the distribution of the actual hydrologic monitoring sites, many river reaches actually do not measure hydrologic data. For the river reach sub-calculation unit, if the river reach of the water environment functional area to which the river reach sub-calculation unit belongs does not have an actual hydrologic monitoring site, the original hydrologic data needs to be preprocessed according to the production convergence relation in the river reach, and other river reach without actually measured hydrologic data are restored through interpolation.

When the hydrologic stations are arranged at the upstream and the downstream of the river reach of the water environment functional area to which a certain sub-computing unit belongs, the actual monitoring value (Q) in the current month of the upstream and the downstream monitoring stations can be used^{On the upper part}、Q^{Lower part}) And estimating the average flow of the river reach of the water environment functional area by an interpolation method, wherein the calculation formula is as follows:

wherein Q is the result of accounting the flow of a river section lacking hydrologic monitoring data, m³/s；Q^{On the upper part}、Q^{Lower part}Measured flow of a month, m, of upstream and downstream hydrological stations, respectively³S; a is the average water yield of the river basin above the control section of the data station for many years, m³；A^{On the upper part}、A^{Lower part}Average water yield m in many years in the watershed controlled by upstream and downstream hydrological stations respectively³。

the meteorological data in this embodiment is derived from the average precipitation per year data in the resource and environment scientific data center of the academy of sciences in china, and the average precipitation distribution data over many years in the water allocation domain is intercepted with the aid of the ArcGIS spatial data processing technique. Obtaining the average rainfall distribution and the water runoff producing deep space of the 10 water flow domain 1956 + 2000 years.

The steady-state flow balance equation is suitable for each simulated river reach, and the water balance equation of the river reach unit is as follows:

Q_i＝Q_i-1+Q_in,i-Q_out,i

All incoming flows from the source can be expressed as:

wherein Q is_ps,i,jIs the flow of the j point source into the river reach i, m³Psi is the number of all point sources in the river reach i, Q_nps,i,jIs the flow of the jth non-point source flowing into the river section i, m³And/d, npsi is the number of all non-point sources in the river reach i.

All the outgoing flow from the source can be expressed as:

The water quality model in the embodiment estimates the average flow velocity condition according to the flow by adopting a water level flow relation curve method based on the principle of mass conservation. The specific idea is that the relationship between the flow velocity and the flow and the relationship between the depth and the flow in the river reach unit can be described by a power exponent equation:

U＝aQ^b

H＝cQ^d

wherein Q is the flow rate, m³S; u is the average flow velocity, m/s; h is the average water depth, m; a. b, c and d are empirical constants and can be obtained by calculating intercept and slope of a water level-flow relation curve of a cross section.

The basic theory of the water environment model of the watershed is a one-dimensional advection-diffusion and mass conservation equation, the model is suitable for the dendritic river, and allows the discharge of wastewater from a plurality of point sources along the river, the entry and collection of surface sources, the water intake and the inflow of tributaries to analyze the influence of the total pollutant discharge amount and the specific discharge position on the water quality of the received water body, and the model can be used as a steady-state model or a time-varying dynamic model to simulate sudden water environment pollution accidents and the like.

The river reach sub-calculation unit is considered to be in a stable state, namely the concentration of the pollutants in the river reach is only related to the position of the sewage discharge outlet and is not related to the time, the time control is determined by the hydraulic retention time, and the hydraulic retention time is determined by the length of the river reach and the average flow speed of the river reach. Consider advection diffusion, dilution, and biochemical reactions of the material components themselves, interactions between water quality components, and the influence of the external source and drain of the components on the concentration of the components.

For the water quality change caused by point source and non-point source blowdown along the moisture trunk, performing simulation analysis by adopting a constant blowdown one-dimensional steady state degradation water quality model:

for the case that the flow velocity of the small branch flow surface has little change, the formula is as follows:

C₀＝(C_pQ_p+C_hQ_h)/(Q_p+Q_h)

after the sudden water environment risk accident pollution discharge process is analyzed, accident pollution discharge influences water quality change of the trunk branch of the lower water, and degradable pollutants, such as COD, ammonia nitrogen and other conventional pollutants, degradable toxic and harmful organic pollutants, acid and alkali and the like, have the following formula:

The embodiment computes the yield of the non-point source pollutant of the water flow domain by using an output coefficient model. The output coefficient method is firstly proposed in North America in the early 70 th of the 20 th century, and is characterized in that the method can directly utilize data such as land utilization conditions, planting industry structures and the like, and utilizes the pollutant output coefficient to estimate the non-point source pollution load output by a drainage basin, so that the method is a lumped non-point source pollution load simple and convenient estimation method.

The output coefficient model is a concrete embodiment of an output coefficient method, is a mathematical weighting formula for calculating annual average pollution such as total nitrogen, total phosphorus and the like on a watershed scale by using a semi-distributed approach, and is a semi-distributed lumped model in essence. Because the source pollution load of the drainage basin is closely related to the land utilization type in the drainage basin, the relationship between the drainage basin land utilization type and the non-point source pollution output quantity is directly established by utilizing data such as the drainage basin land utilization type which is relatively easy to obtain through multivariate linear correlation analysis, and then the total load of the area pollution is obtained by summing the pollution loads from different sources.

The generation amount of urban living pollution is determined according to pollution discharge coefficients of town and town population in the water distribution domain, as shown in the following formula:

W＝3.65AF

wherein W is the urban life pollution load, t/a; a is urban population, ten thousand; f is the domestic pollution discharge coefficient of urban residents, g/person.day.

According to the pollution discharge coefficient and the use instruction of the Source of Life (2011 revision) and the quota of Water consumption for Qinghai province (DB63T 1429) 2015) and combining the development level of local socioeconomic, the quota of the urban population domestic water of Wening city and Shandong city in the Water flow area is 230L/person.day, the pollution coefficient of COD (chemical oxygen demand) product is 72 g/person.day, the pollution coefficient of ammonia nitrogen product is 8.06 g/person.day, and the pollution coefficient of total phosphorus product is 0.89 g/person.day; the daily water quota of residents in urban areas of other counties and towns and general towns is 150L/person.day, the COD yield pollution coefficient is 61 g/person.day, the ammonia nitrogen yield pollution coefficient is 7.41 g/person.day, and the total phosphorus yield pollution coefficient is 0.63 g/person.day.

In this study, the non-point source pollution load of livestock and poultry breeding industry is calculated as follows:

Q＝∑A_i*T_i*E_j

production of livestock and poultry pollutants (T)_i) For livestock and poultryThe daily excretion coefficient of fecaluria (kg/head-year) x the fecaluria contaminant content (g/kg).

The excretion coefficients of 5 livestock and poultry such as pigs, cows, beef cattle, laying hens, broilers and the like, and the contents of various pollutants such as COD, ammonia nitrogen, total phosphorus and the like in excrement of the livestock and poultry refer to the recommended value of the original national environmental protection Bureau and the first national pollution Source general survey: a livestock and poultry breeding industry source pollution discharge coefficient manual (2009) recommended value.

TABLE 1 daily excretion coefficients of five main types of livestock and poultry feces

TABLE 2 average contaminant content in feces of five main types of livestock and poultry

TABLE 3 fouling coefficient of five main types of livestock and poultry

Breed species	COD (g/head. sky)	Ammonia nitrogen (g/head. sky)	Total phosphorus (g/head. sky)
				Live pig	133.7	10.82	8.45
Beef cattle	680	69	28
				Dairy cow	680	69	28
Laying hen	4.57	0.28	0.58
				Broiler chicken	4.57	0.28	0.58

TABLE 4 average treatment efficiency of typical fecal sewage treatment mode

The research adopts a standard farmland method to estimate the non-point source runoff of the planting industry. The standard farmland refers to a farmland in plain, with wheat as a planted crop, loam as a soil type, a fertilizer application amount of 25-35 kg/mu per year and a precipitation amount within the range of 400-800 mm.

A. slope correction

The land gradient is below 25 degrees, and the loss coefficient is 1.0-1.2; over 25 degrees, and the loss coefficient is 1.2-1.5. According to the research, the average gradient of the cultivated land is analyzed under an ArcGIS platform according to the DEM data of the drainage basin and the land utilization data, and a corresponding correction factor is determined.

B. Crop type correction

The method is characterized in that main crops such as corn, sorghum, wheat, barley, rice, soybean, cotton, oil plants, sugar materials, economic forests and the like are used as research objects, and the pollutant loss correction coefficients of different crops are determined. The correction coefficient needs to be verified through scientific research experiments or empirical data. The central watershed mainly plants the crop type being wheat.

C. Soil type correction

D. Chemical fertilizer application amount correction

E. Precipitation correction

The annual rainfall is below 400mm, and the loss coefficient is 0.6-1.0; taking the loss coefficient to be 1.0-1.2 in areas with annual rainfall between 400 and 800 mm; the annual rainfall in the area with the annual rainfall above 800mm is taken to have the loss coefficient of 1.2-1.5. The average annual precipitation of the drainage basin is 600-300mm, and a precipitation correction factor is determined according to an annual precipitation map and a farmland distribution map of the drainage basin.

in the formula, E_PlantingThe discharge amount of the load is ton/year for the drainage basin planting industry; e_{Standard farmland}The loss coefficient is the loss coefficient of the planting mode of the 'standard farmland' in the drainage basin, namely kilogram/mu.year; a. the_{Planting Pattern i}Adopting planting area of i-th planting mode for the drainage basin, mu; a is_{Slope correctionIs just}The gradient correction factor is a non-dimensional gradient correction factor; b_{Crop type correction}The crop type is corrected, and the method is dimensionless; c. C_{Soil type correction}The soil type correction is carried out, and the dimension is not needed; d_{Chemical fertilizer application amount correction}The fertilizer application amount is corrected, and no dimension is needed; e.g. of the type_{Precipitation correction}The method is used for correcting the precipitation amount and is dimensionless;

the pollution discharge coefficient of the planting industry covers the farmland fertilizer loss coefficients of different planting modes of main planting areas, planting modes, farming modes, farmland types, soil types, terrain and main crop types in China according to 'first national pollution source census-agricultural pollution source (fertilizer loss coefficient)' (2009) published by a lead group office of the first national pollution source census of the state institute, and the farmland fertilizer loss coefficients of typical planting modes of a water basin of a vertical water flow field are as shown in the table:

TABLE 5 Farmland nitrogen and phosphorus nutritive salt loss coefficient in typical planting mode of northern drainage basin

Planting pattern	Ammonia nitrogen loss coefficient (kg/mu-year)	Total phosphorus loss coefficient (kg/mu-year)
			Northern plateau mountain area-gentle slope land non-terrace-dry land-garden land	0.085	0.041
Northern plateau mountain area-steep slope non-terrace-dry land-field	0.006	0.003
			Northern plateau area-gentle slope terrace-dry land-garden land	0.007	0.002
Northern plateau mountain area-steep slope terrace-dry land-field	0.001	0.001

In this study, the rural domestic pollution emission situation in the water watershed is determined according to the pollution load emission of the rural population and the average rural population of each control sub-control unit, as shown in the following formula:

W＝3.65AF

in the formula, W is the rural area source load discharge amount, ton; a is rural population, ten thousand people; f is the coefficient of pollution discharge of rural residents, g/(man-day).

According to the socioeconomic statistics data of the watershed, there are 155.8 ten thousand rural demographics in 2015 year in 12 counties of the watershed. The rural resident life emission coefficient of the watershed is 80L/person/day according to the Qinghai province water quota (DB63T1429-2015), the rural life main pollution load generation coefficient reference and the town life coefficient are respectively calculated by 61 g/person/day, 7.41 g/person/day and 0.63 g/person/day.

The embodiment adopts a standard urban pollution discharge coefficient method to estimate the urban runoff surface source runoff quantity. The definition of the so-called standard city is: is located in plain zone, the urban non-agricultural population is between 100 and 200 thousands, and the area of the built-up area is 100km²And on the left and right, the annual precipitation is between 400 and 800mm, the popularity of the urban rainwater collection pipe network is between 50 and 70 percent, and the standard urban source intensity coefficient is COD 50 tons/year and ammonia nitrogen 12 tons/year.

A. coefficient of terrain correction

B. Population correction factor

C. Area correction factor

D. Rainfall correction factor

E. Pipe network correction factor

The urban non-point source accounting formula is as follows:

E_city＝E_{Standard city}×T_City×P_City×A_City×R_City×P_{n city}

The embodiment solves the problem of water-land coupling between a pollution source and a river water system through the sewage draining exit generalization. Point source and non-point source pollution loads must be distributed to the corresponding waste outlets. While the model allows a single drain to correspond to virtually any number of point or non-point sources of pollution.

The point source determines the sub-calculation unit to which the point source belongs according to the actual position of the point source, a plurality of adjacent point source sewage outlets or water intakes are simplified into a concentrated sewage outlet or water intake, and the distance between the combined sewage outlet and the upstream section can be calculated by the following formula:

in the formula, L is the distance, km, from a generalized sewage discharge outlet to a control section at the upstream of a river reach; q_iThe amount of water of the ith sewage discharge outlet m³/s：C_iThe pollutant concentration of the ith sewage outlet is mg/L; l is_iThe distance, km, from the ith sewage draining exit to the upstream control section of the river reach.

In the established moisture model of the watershed, the association processing steps of the pollution source and the drain outlet are as follows: 1) firstly, establishing a drain outlet-pollution source attribute table, and determining the relation between a drain outlet (water) and a pollution source (land); 2) calculating the sink entering distance from the point source to the sewage outlet; 3) determining river entering coefficients according to the river entering distance; 4) and accumulating all pollution sources of a certain sewage discharge outlet to obtain the river sewage amount and the pollution load concentration of the sewage discharge outlet.

In the embodiment, for the quality of source head water of each trunk branch river of the lunge river, the quality of type II water is considered according to the quality standard of surface water environment (GB3838-2002), wherein the concentration of COD source water is 10mg/L, and the concentration of ammonia nitrogen is 0.25 mg/L.

And (3) distributing 19 main water quality monitoring sections in the watershed, and verifying the parameters by using a set of data which is independent of parameter rate timing. In the research, the average relative errors of actually measured chemical oxygen demand and ammonia nitrogen water quality concentration of water quality monitoring sections of three main river sections, namely a dry, flat and rich water dry flow zamalon-xinning bridge section, a small fjord-bay bridge section, a bay bridge-min and bridge section and the like in the same water period are selected as error detection indexes, and the statistical result of the average relative errors of all the sections is shown in table 6.

TABLE 6 Water dry flow Main section 2014 year Water phase simulation and prediction Water quality contrast

From simulation and validation results, the global average relative error of the dry fluid chemical oxygen demand of the moisture is 7.6%, and the global average relative error of the ammonia nitrogen is 11.5%, i.e. the total accuracy of the chemical oxygen demand reaches 92.4%, and the total accuracy of the ammonia nitrogen reaches 88.5%. The model parameter verification result shows that the simulation precision of the one-dimensional water quality model is basically over 85 percent, the response characteristics of drainage basin pollutant discharge and water quality can be accurately reflected, and the simulation precision is high.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the claims.

Claims

1. A water quality simulation method based on water environment quality target management of a control unit is characterized by comprising the following steps: the method comprises the following steps:

(1) establishing a database, comprising: the drainage basin geographic information database is used for recording the geographic information data of the drainage basin; the hydrological, meteorological and water quality monitoring database is used for recording hydrological and water quality data in a flow domain and meteorological monitoring data corresponding to the meteorological station; the drainage basin environmental statistics database is used for collecting the emission data of various pollution sources of the drainage basin, and the social and economic and demographic information data of the drainage basin; the model parameter database is used for recording the pollution discharge coefficient of a typical pollution source, the river entering coefficient of the pollution source, the conventional pollutant transmission-degradation coefficient and the toxic and harmful substance transmission-degradation coefficient;

(2) preliminarily dividing the river into a plurality of non-uniform river sections, dividing each river section into a plurality of sub-computing units, and finally determining sub-computing unit grids of the whole watershed water system;

(3) calculating the non-point source pollution yield by adopting a drainage basin non-point source pollution discharge model; analyzing the non-point source pollution discharge characteristics in each control unit, extracting data in a drainage basin environment statistical database, a drainage basin geographic information database, a hydrological, meteorological and water quality monitoring database and a model parameter database, and calculating the non-point source pollutant generation amount in a pollution source by adopting a drainage basin non-point source pollution discharge coefficient model; the non-point sources comprise urban living sources, livestock breeding sources, planting industry surface sources, rural living surface sources and urban non-point sources;

(4) determining the hydrological conditions of the river reach by adopting a hydrological calculation method; analyzing hydrological meteorological characteristics of the river reach, analyzing the availability of hydrological data, and selecting an applicable hydrological interpolation method: if hydrologic monitoring sites are arranged at the upstream and the downstream of the existing river reach, extracting flow data in the hydrologic, meteorological and water quality monitoring databases, and calculating the flow of the river reach by adopting a natural runoff reduction method; when the river reach lacks upstream and downstream hydrological monitoring sites, hydrological data of the drainage basin can be extracted, the river reach with basically the same hydrological conditions is found, and the flow of the river reach is estimated by adopting a hydrological comparison method; further calculating the water surface area and the water volume of the river reach based on the flow;

(5) based on the calculated data in the steps (3) and (4), simulating the water quality of the sub-calculating unit by adopting a watershed one-dimensional river network hydrodynamic water quality model method, wherein the method comprises the following steps: the method comprises the following steps of firstly, extracting position information of a pollution source, a sewage outlet and a water intake in a drainage basin geographic information database, and generalizing adjacent sewage outlets in the same sub-computing unit; extracting various point source discharge data in the drainage basin environment statistical database and the calculation result in the step (3), and further calculating the river inflow sewage quantity and the pollution load concentration of the pollutants at the sewage discharge outlet after generalization according to the river inflow coefficient in the model parameter database; calculating the flow speed condition of the river reach by adopting a river water dynamic model method according to the calculation result of the step (4); secondly, verifying and calibrating the one-dimensional water quality model by adopting independent data, so that the simulation precision of the one-dimensional water quality model is not lower than 80%; and calculating the grid pollution load concentration of each sub-calculation unit by adopting the verified and calibrated water quality model.

2. The water quality simulation method based on control unit water environment quality target management as claimed in claim 1, wherein the geographical information data of the watershed recorded by the watershed geographical information database comprises land area range, administrative division, river system, terrain and landform, hydrological meteorological site, water quality monitoring section, and position information of various pollution sources, sewage outlets and water intakes.

3. The water quality simulation method based on control unit water environment quality target management according to claim 1 or 2, characterized in that in the step (5), the method further comprises the steps of: and extracting the degradation coefficient in the conventional pollutant transmission or toxic and harmful substance transmission-degradation coefficient database in the model parameter database by using the river one-dimensional sudden risk accident simulation model, and simulating the change condition of the water quality of the downstream drainage basin after sudden water environment risk accidents are discharged.

4. The water quality simulation method based on control unit water environment quality target management of claim 1, wherein the river hydrodynamic model method comprises a river level-flow relation method, a Manning formula method; the watershed one-dimensional river network hydrodynamic water quality model method comprises a river constant pollution discharge one-dimensional steady-state water quality degradation model.

5. The water quality simulation method based on control unit water environment quality target management according to claim 1 or 2, characterized in that in the step (5), when the sewage outlets are generalized, as for the sewage outlets of the point source, a plurality of adjacent sewage outlets in the same sub-computing unit grid can be generalized into a centralized sewage outlet; the method for calculating the river sewage amount and the pollution load concentration of the pollutants at the sewage outlet comprises the following steps: 1) determining the corresponding relation between the sewage draining exit and the pollution source; 2) calculating the sink-in distance from the pollution source to the sewage outlet; 3) determining river entering coefficients according to the river entering distance; 4) and accumulating all pollution sources of each sewage discharge outlet to obtain the river sewage amount and the pollution load concentration of the sewage discharge outlet.

6. The water quality simulation method based on control unit water environment quality target management of claim 3, characterized in that a non-point source sewage discharge outlet is generalized to a line discharge outlet along the course of a river reach, and the point positions of the starting point and the ending point of each non-point source affected river reach are used as boundary lines to evenly distribute the pollution source load to each affected sub-computing unit grid within the range.

7. The water quality simulation method based on the water environment quality target management of the control unit according to claim 1 or 2, wherein the river reach with basically the same water power, water quality characteristics and parameter values in the step (2) is divided into the same river reach, and the water power and/or water quality characteristics of each river reach are different; the sub-calculation units are the minimum units for water quality simulation, and each river reach is composed of an integral number of sub-calculation units.

8. The water quality simulation method based on control unit water environment quality target management according to claim 1 or 2, characterized in that the divided river segments and the sub-calculation units are respectively encoded according to the river from a main stream source to a drainage basin outlet so as to clarify the connection and intake-sink topological relation between river networks.

9. The water quality simulation method based on control unit water environment quality target management of claim 7, wherein the river reach with basically same water power, water quality characteristics and parameter values is divided into the same river reach, and then the river reach with a sensitive point is further divided into an upstream independent river reach and a downstream independent river reach at the sensitive point, wherein the sensitive point comprises any one of the following positions: the control unit divides a boundary; water environment function partitioning; the junction of the river stem and the branch; a water quality monitoring station; where the hydraulic characteristics are changed significantly, wherein the hydraulic characteristics refer to any one of flow speed, water depth and river width; at the tidal river reach boundary.

10. The water quality simulation method based on control unit water environment quality target management of claim 7, wherein all sub-computing unit grids are divided into: the source head water unit grid is source head water of a drainage basin; the tributaries are imported into the sink unit grids, and non-source water unit grids into which the tributaries are imported; common unit grids without non-source water unit grids for branch flow import;

for the source water unit grid, a sink is arranged in the middle of the source water unit grid; and for the tributary import and export unit grid, the tributaries are gathered to be imported at the upstream start position of the tributary import and export unit grid, and the drain outlet is gathered to be the position where the tributary import and export unit grid is placed in the middle.