Estuary coast water quality forecasting method based on hydrodynamic water quality coupling model

Abstract

The invention provides an estuary coast water quality forecasting method based on a hydrodynamic water quality coupling model. The method comprises the following steps: S1, collecting basic data required for constructing an estuary coast hydrodynamic water quality model; s2, establishing and verifying an estuary coast hydrodynamic water quality coupling model based on an FVCOM-ERSEM model; s3, utilizing the verified model to simulate wave and water flow coupling motion and pollutant space-time distribution in the estuary coast area within a set time; s4, key factors influencing estuary coast hydrodynamic force and pollutant transportation are concluded through monitoring, literature and investigation; s5, sensitivity analysis is carried out, and the spatial-temporal change rule of pollutants in the estuary coast area under different factors is studied; and S6, analyzing the influence of the change of various factors on the pollutant concentration by taking the water quality parameters as indexes. According to the method, influences of engineering construction, pollutant discharge and other factors on water quality parameters are identified through quantitative analysis, and the model fitting degree is improved by adopting a high-precision grid technology.

Description

Technical Field

[0001] The invention relates to the technical field of water quality prediction, and in particular to an estuary and coastal water quality prediction method based on a hydrodynamic-water quality coupling model. Background Art

[0002] The estuary coast is the intersection of land and sea, and is an important window for the inland to open up to the outside world. Due to its superior geographical location, good natural conditions, rich tidal flats and coastline resources, and large space for development and utilization, it has become a population gathering place, social and economic development center, and important transportation hub for coastal countries. In the past few decades, a large number of people have gathered in the estuary coast, and in the process of urbanization and industrialization, human activities such as coastal engineering construction, inter-basin water transfer, reclamation, and pollutant discharge have not only generated huge production benefits and economic benefits, but also led to a sharp change in the hydrodynamic elements of the estuary coast and the deterioration of the water environment. Specifically, human development activities have led to significant changes in environmental elements such as coastline, riverbed morphology, surface cover, engineering and its structures, and hydrodynamic conditions such as tidal range, water flow, tidal volume, and waves have also changed and become more complex. The spatiotemporal response of the hydrodynamic characteristics and hydrodynamic environment of the estuary coast to large-scale development activities has broken its original dynamic balance, and the renewal capacity and self-purification capacity of the estuary coast water body have changed, thus significantly affecting the spatiotemporal distribution of pollutants. Pollutants generated during human development are discharged into estuarine and coastal water systems, resulting in serious water pollution and frequent disasters such as oil spills, salt tides, eutrophication and red tides.

[0003] With the rapid development of computer hardware technology, numerical algorithms and water environment dynamics theory, hydrodynamic and water quality models have evolved from the initial one-dimensional models to the current complex three-dimensional models, and more and more influencing factors and parameters are considered. At present, water quality models such as WASP, QUAL2E, SWAT, ERSEM and MIKE series have been established and used in the study of hydrodynamics and water environment in oceans, estuaries, lakes, coasts and other waters. However, due to the frequent interference of human development activities, the evolution mechanism of hydrodynamics in estuary and coastal environments is extremely complex, coupled with the large-scale emission of pollutants, the response mechanism of material migration and transformation, and the temporal and spatial distribution of pollutant elements are still unclear. The above problems have posed new technical challenges to estuary and coastal water quality simulation and water environment forecasting.

[0004] The FVCOM hydrodynamic model is a three-dimensional free surface, unstructured grid and finite volume ocean circulation model. It uses the finite volume method to solve three-dimensional equations to better meet the conservation of mass and momentum, and uses unstructured triangular grids to fit complex coastlines and terrain. The FVCOM model can be coupled with multiple models such as wave models, sediment models, sea ice models and water quality models, and has been applied to hydrodynamic and water quality simulations in many rivers, lakes, reservoirs, estuaries and coastal areas around the world.

[0005] The ERSEM model is an ecodynamic model that can be used to describe the biogeochemical processes at lower trophic levels in estuaries and coasts. It describes the biogeochemical cycle processes of elements such as carbon, nitrogen, phosphorus, silicon and oxygen in water and benthic ecosystems by constructing and solving a set of differential equations.

[0006] How to understand the migration and transformation laws of pollutants in the complex dynamic field of estuaries and coasts and the spatiotemporal response mechanism to human activities, repair and manage the deteriorated coastal water environment, and scientifically develop estuaries and coasts to achieve a balance between water environment protection and social and economic development has become an important challenge facing government managers and scientific researchers. Therefore, it is urgent to provide an efficient and high-precision simulation method for the transport and transformation of pollutants in the complex dynamic field of estuaries and coasts, which is also an aspect of concern in the context of estuary and coastal engineering construction, deteriorated water environment management and restoration, and the coordinated sustainable development of water ecological environment and social economy. Summary of the invention

[0007] The purpose of the present invention is to provide an estuary and coastal water quality forecasting method based on a hydrodynamic-water-quality coupling model, in order to improve the simulation accuracy of water quality simulation and forecasting, in view of the fact that there are many factors affecting the water quality migration and transformation process and the spatiotemporal distribution in the context of estuary and coastal development, and the errors are large.

[0008] To achieve the above object, the present invention adopts the following technical solution:

[0009] A method for predicting estuary and coastal water quality based on a hydrodynamic-water quality coupling model comprises the following steps:

[0010] S1: Select an appropriate research scope based on the forecast location and collect the basic data required for the construction of estuarine and coastal hydrodynamic and water quality models;

[0011] S2: Establish a coupled model of estuarine and coastal hydrodynamics and water quality based on the FVCOM-ERSEM model, and verify and calibrate the model;

[0012] S3: Based on the calibrated estuarine and coastal hydraulic water quality model, the coupled motion process of waves and currents in the estuarine and coastal areas and the spatiotemporal distribution characteristics of pollutants within a set time are obtained;

[0013] S4: Summarize the key factors affecting estuarine and coastal hydrodynamics and pollutant transport through field monitoring, literature and field investigation;

[0014] S5: Conduct sensitivity analysis based on the calibrated estuarine and coastal hydraulic water quality model to obtain the temporal and spatial variation patterns of pollutants in the estuarine and coastal areas within a set time under different factors;

[0015] S6: Taking the water quality parameters of estuarine and coastal areas as the key indicators of estuarine and coastal water environment, comparative analysis is performed to obtain the specific pollutant concentration variables caused by changes in various factors.

[0016] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0017] As a preferred technical solution of the present invention: the basic data in step S1 includes hydrological data of estuaries and coasts, meteorological data, hydraulic and water quality data, river section grid elevation data, terrain data and shoreline data.

[0018] As a preferred technical solution of the present invention: the step S2 further includes the following steps:

[0019] S21: Based on the prepared basic data, create a grid file, an initial file and a boundary drive file;

[0020] S22: Set model parameters, run the river water quality model, and output simulation results;

[0021] S23: According to the error analysis between the simulation results and the measured values, the model parameters are dynamically adjusted and the model is calibrated.

[0022] As a preferred technical solution of the present invention: the grid file is established in step S21 as follows: first, the estuary coast is divided into a certain number of unstructured triangular grids, and the key areas are encrypted, and then the water depth of each grid is obtained by the difference of measured terrain data.

[0023] As a preferred technical solution of the present invention: the boundary driving file in step S21 includes hydrodynamic boundaries, meteorological boundaries, and water quality boundaries, wherein the water quality boundaries also include nutrients, temperature, salinity, chlorophyll, and inorganic matter.

[0024] As a preferred technical solution of the present invention: the model parameters in step S22 include time step, bottom friction coefficient, material convection and diffusion coefficient, and various water quality reaction kinetic coefficients.

[0025] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0026] The present invention provides an estuary and coastal water quality prediction method based on a hydrodynamic and water quality coupling model, which has the following beneficial effects: it can quantitatively identify the influence of engineering construction, pollutant discharge, hydrodynamics, and natural environment on water quality parameters such as nutrients, salinity, and phytoplankton, and at the same time adopt unstructured triangular grids to improve the fitting degree of key focus areas and complex areas, so as to solve the problem that the traditional environmental hydrodynamic model in the prior art considers too few factors for estuary and coastal water quality and has low simulation accuracy; based on the estuary and coastal hydrodynamic and water quality model, it can predict and analyze water environment problems such as eutrophication, salt tide, red tide, etc., so as to propose more accurate and effective river pollution control measures, which is of great significance for estuary and coastal pollutant control; in addition, the present invention reveals the spatiotemporal response mechanism of estuary and coastal hydrodynamics and water quality, combines the water environment carrying capacity, and provides technical support and theoretical guidance for estuary and coastal development from the perspective of water pollution prevention and control.

[0027] Taking human activities (pollutant discharge, engineering construction, etc.) as the core driving force for the spatiotemporal evolution of estuarine and coastal water quality, a method for estuarine and coastal water quality forecasting under the influence of human activities is proposed in combination with monitoring and theoretical analysis, aiming to solve the problems of pollutant migration, transformation and control in estuarine and coastal areas, and to provide a reference for hydrodynamic water quality monitoring and pollution control in estuarine and coastal areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention provides a flow chart of the method for predicting estuary and coastal water quality based on the hydrodynamic-water-quality coupling model.

[0029] Figure 2 The following is an overview of the Pearl River Estuary region in the embodiment of the present invention, wherein: (a) is a location map, (b) is a map of terrain, important cities and Pearl River tributaries, wherein HM, JM, HQM, HEM, MDM, JTM, HTM and YM represent Humen, Jiaomen, Hongqilimen, Hengmen, Modaomen, Jitimen, Hutiaomen and Yamen respectively; ①-⑤ represent Longxue Island, Wanqingsha, Hengmen Beach, Qiaoao Island and Gaolan Island respectively.

[0030] Figure 3 This is the verification of the hydrodynamic model of the Pearl River Estuary region in the embodiment of the present invention.

[0031] Figure 4 This is the verification of the water quality model of the Pearl River Estuary region in the embodiment of the present invention.

[0032] Figure 5The distribution of surface water quality parameters in the Pearl River Estuary in 1990 and the changes in water quality parameter distribution caused by shoreline changes from 1990 to 2020 in the embodiment of the present invention, wherein: (a), (c), (e), and (g) are the distribution of suspended sediment, nitrate, ammonium salt, and silicate in 1990, respectively; (b), (d), (f), and (h) are the changes in the distribution of these four water quality parameters, respectively. DETAILED DESCRIPTION

[0033] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 As shown, a method for predicting estuary and coastal water quality based on a hydrodynamic and water quality coupling model comprises the following steps:

[0035] S1: Select an appropriate research scope based on the forecast location and collect the basic data required for the construction of estuarine and coastal hydrodynamic and water quality models;

[0036] S2: Establish a coupled model of estuarine and coastal hydrodynamics and water quality based on the FVCOM-ERSEM model, and verify and calibrate the model;

[0037] S3: Based on the calibrated estuarine and coastal hydraulic water quality model, the coupled motion process of waves and currents in the estuarine and coastal areas and the spatiotemporal distribution characteristics of pollutants within a set time are obtained;

[0038] S4: Summarize the key factors affecting estuarine and coastal hydrodynamic movement and pollutant transport (natural environment, pollutant emissions, extreme marine disasters) through field monitoring, literature and field investigation;

[0039] S5: Conduct sensitivity analysis based on the calibrated estuarine and coastal hydraulic water quality model to obtain the temporal and spatial variation patterns of pollutants in the estuarine and coastal areas within a set time under different factors;

[0040] S6: Taking the water quality parameters of estuarine and coastal areas as the key indicators of estuarine and coastal water environment, comparative analysis is performed to obtain the specific pollutant concentration variables caused by changes in various factors.

[0041] The basic data in step S1 include geographical data (topographic data and shoreline data) of the estuary and coast, meteorological data (temperature, air pressure, light, etc.) and hydrological data (hydraulic and water quality data, river section grid elevation data) of the estuary and coast area.

[0042] Step S2 also includes the following steps:

[0043] S21: Based on the prepared basic data, necessary files such as mesh files, initial files and boundary drive files are created;

[0044] S22: Set model parameters, run the river water quality model, and output simulation results;

[0045] S23: According to the error analysis between the simulation results and the measured values, the model parameters are dynamically adjusted and the model is calibrated.

[0046] Model coupling: The framework of aquatic biogeochemical models (FABM) is a program that can provide coupling protocols for biogeochemical models of aquatic systems. As a domain-independent programming framework, it can realize the coupling of hydrodynamic models and water quality models through interfaces with different functions, which has the advantages of not changing the internal structure of the numerical model and being very simple to apply. The present invention adopts the FABM framework to realize the coupling of the FVCOM hydrodynamic model and the ERSEM water quality model. In the process of model coupling, the FABM framework itself does not participate in the calculation and storage of the results of the water body movement process and the water ecological environment process. These functions are respectively assigned to the FVCOM hydrodynamic model and the ERSEM water quality model by the FABM framework. The FVCOM hydrodynamic model is responsible for storing physical variables, inputting and outputting data, and carrying out calculations such as convection, diffusion and time integration of water bodies and substances. The ERSEM model is responsible for defining the biogeochemical variables contained in it and their relationship with external physical elements, providing the environment, source and sink, boundary flux, vertical transport velocity and other conditions required for the operation of the model, and calculating the biogeochemical process of water quality variables. In addition, the integration of total chlorophyll, total primary productivity, and total carbon in the entire calculation process is implemented within the FABM framework, which facilitates the verification of energy and mass conservation.

[0047] In terms of model calculation, the finite volume method is used to discretize the dynamic equations, the improved fourth-order Runge-Kutta method is used to time-integrate the control equations, the second-order upwind scheme is used to discretize the advection term, and the central difference implicit scheme is used to discretize the vertical diffusion.

[0048] The specific steps of establishing the grid file in step S21 are as follows: first, the estuary coast is divided into a certain number of unstructured triangular grids, and the key areas and complex areas are encrypted to achieve a balance between calculation accuracy and calculation efficiency. Then, the water depth of each grid is obtained by the difference of measured terrain data. The water depth of each grid is obtained by the difference of measured terrain data.

[0049] In step S21, the initial file sets the simulation time series, time step, initial concentration of water quality parameters, initial water level and flow rate, model parameters and other conditions according to the simulation requirements.

[0050] The boundary driving file in step S21 includes the hydrodynamic boundary, surface meteorological boundary, and water quality boundary of the upstream estuary and the open sea, wherein the hydrodynamic boundary includes river runoff, tide level, and wave height; the surface meteorological boundary includes relative humidity, wind field, cloud cover, atmospheric temperature, light, rainfall, and evaporation; and the water quality boundary also includes nutrients, temperature, salinity, chlorophyll, and inorganic matter.

[0051] The model parameters in step S22 include time step, bottom friction coefficient, material convection and diffusion coefficient, and various water quality reaction kinetic coefficients.

[0052] In step S23, the model calibration includes the calibration of the hydrodynamic module and the water quality module parameters, wherein the hydrodynamic module calibration includes water level, flow velocity, temperature, salinity, suspended sediment concentration, wave height, and wave period; wherein the water quality module calibration includes various water quality parameters such as nutrient solution, inorganic matter, and chlorophyll. The actual monitoring data of the model simulation river section is selected to calibrate the model and adjust the model parameter settings to optimize the model results.

[0053] The main factors affecting the transport and transformation of pollutants and the spatiotemporal evolution of parameters in estuaries and coasts are mainly reflected in the following two aspects: changes in environmental factors such as coastline and topography during estuary and coastal development affect the flow field structure, further changing the water renewal and self-purification capabilities, and the transport and transformation of pollutants and the spatiotemporal distribution of parameters change accordingly; changes in the types and quantities of pollutant emissions in estuaries and coasts change the spatiotemporal distribution of pollutant parameters in estuaries and coasts; under the influence of human activities, extreme disasters such as ocean storm surges and swells have increased, and the extreme dynamic environment of estuaries and coasts has led to changes in the transport and transformation of pollutants and the spatiotemporal distribution of parameters.

[0054] Specifically, the above-mentioned estuary and coastal water quality prediction method based on the hydrodynamic and water quality coupling model is implemented in the following way:

[0055] like Figure 2-5 As shown in the figure, the coastline of the Pearl River Estuary is drawn based on remote sensing images and basin water system maps, and the Pearl River Estuary area is divided into 39,729 calculation grids, and the measured Pearl River Estuary terrain data is interpolated onto each grid. Meteorological data, hydrological data, water quality data, etc. from 1990 to 2020 are collected, and model input files are made and model calculation parameter conditions are set to run the model. The model is calibrated with measured data such as the Pearl River Estuary tide level and water quality parameters, and a Pearl River Estuary hydrodynamic and water quality coupling model is constructed to simulate the migration and transformation process and spatiotemporal distribution characteristics of pollutants in the Pearl River Estuary.

[0056] Taking the shoreline changes during the development of the Pearl River Estuary as a typical working condition, the temporal and spatial changes of water quality parameters in the Pearl River Estuary before and after the shoreline changes from 1990 to 2020 were analyzed. The construction of reclamation projects near Longxue Island, Wanqingsha, Hengmen Beach and Modaomen narrowed the river channel and hindered the transportation and diffusion of sediment in the river channel, so the suspended sediment concentration in the local waters decreased. At the same time, the reduction of residual flow at the mouth after the reclamation project weakened its water exchange capacity with the open sea, which further led to an increase in the suspended sediment concentration at the mouth. The increase in suspended sediment concentration in the upper reaches of Huangmaohai was mainly due to the connection project between Gaolan Island and the land, which inhibited the transportation and diffusion of sediment to the open sea. During the reclamation process, nitrate and silicate showed a similar spatial variation trend as suspended sediment in most areas of the Pearl River Estuary. However, in contrast to the increase in suspended sediment concentration in the western area of ​​Gaolan Island, the concentrations of nitrate and silicate decreased, mainly because the water with high nitrate and silicate concentrations could not be transported from Jitimen to here after the reclamation project. With the growth of algae and the enhancement of their absorption of nutrients in the middle and lower reaches of the Lingdingyang and the northwest of the Huangmaohai Sea, the local nitrate concentration has decreased significantly. Since the reclamation project has promoted the transport and diffusion of phytoplankton from the upper reaches of the estuary to the mouth, the absorption of ammonium by phytoplankton has weakened in the upper reaches and increased at the mouth. Therefore, ammonium salts showed a spatial variation trend opposite to that of nitrates and silicates. In other words, the absorption of ammonium by phytoplankton plays a dominant role in the changes in the transport and metabolization process and spatial distribution of ammonium salts during reclamation.

[0057] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for predicting estuary and coastal water quality based on a hydrodynamic and water quality coupling model, characterized in that: The steps include: S1: Select an appropriate research scope based on the forecast location and collect the basic data required for the construction of estuarine and coastal hydrodynamic and water quality models; S2: Establish a coupled model of estuarine and coastal hydrodynamics and water quality based on the FVCOM-ERSEM model, and verify and calibrate the model; S3: Based on the calibrated estuarine and coastal hydraulic water quality model, the coupled motion process of waves and currents in the estuarine and coastal areas and the spatiotemporal distribution characteristics of pollutants within a set time are obtained; S4: Summarize the key factors affecting estuarine and coastal hydrodynamics and pollutant transport through field monitoring, literature and field investigation; S5: Conduct sensitivity analysis based on the calibrated estuarine and coastal hydraulic water quality model to obtain the temporal and spatial variation patterns of pollutants in the estuarine and coastal areas within a set time under different factors; S6: Taking the water quality parameters of estuarine and coastal areas as the key indicators of estuarine and coastal water environment, comparative analysis is performed to obtain the specific pollutant concentration variables caused by changes in various factors.

2. The method for predicting estuary and coastal water quality based on the hydrodynamic and water quality coupling model according to claim 1, characterized in that: The basic data in step S1 include hydrological data of estuaries and coasts, meteorological data, hydraulic and water quality data, river section grid elevation data, terrain data and shoreline data.

3. The method for predicting estuary and coastal water quality based on the hydrodynamic and water quality coupling model according to claim 1, characterized in that: The step S2 further comprises the following steps: S21: Based on the prepared basic data, create a grid file, an initial file and a boundary drive file; S22: Set model parameters, run the river water quality model, and output simulation results; S23: According to the error analysis between the simulation results and the measured values, the model parameters are dynamically adjusted and the model is calibrated.

4. The method for predicting estuary and coastal water quality based on the hydrodynamic and water quality coupling model according to claim 3 is characterized by: The step S21 of establishing the grid file is as follows: firstly, the estuary coast is divided into a certain number of unstructured triangular grids, and the key areas are encrypted, and then the water depth of each grid is obtained by the difference of the measured terrain data.

5. The method for predicting estuary and coastal water quality based on the hydrodynamic and water quality coupling model according to claim 3 is characterized by: The boundary driving file in step S21 includes hydrodynamic boundary, meteorological boundary and water quality boundary, wherein the water quality boundary also includes nutrients, temperature, salinity, chlorophyll and inorganic matter.

6. The method for predicting estuary and coastal water quality based on a hydrodynamic-water-quality coupling model according to claim 3, characterized in that: The model parameters in step S22 include time step, bottom friction coefficient, material convection and diffusion coefficient, and various water quality reaction kinetic coefficients.

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