An evaluation method to quantify the impact of river and lake topography changes on lake water levels

Abstract

The invention discloses an evaluation method for quantifying the superimposed influence of lake and river topography changes on lake water levels, and belongs to the field of ecological environment and environmental protection technology. The method constructs lake hydrodynamic models of topography of different ages, combines the water level-flow relationship of rivers of different ages, and only requires DEMs of lakes of different ages and water level and flow sequences of large rivers of different ages, so as to construct a rapid evaluation method for the influence of lake and river topography changes on lake water levels, restore the lake water level process before and after the topography changes, quantitatively evaluate the influence of the common changes of lake topography and river topography in the lake and river system on the lake water level, and can quantify the influence of topography changes of both rivers and lakes on the lake water level, so as to provide a scientific basis for the cause analysis, quantitative evaluation and ecological environment impact evaluation of floods and droughts.

Description

Technical Field

[0001] The invention belongs to the field of ecological environment and environmental protection technology, and in particular relates to an evaluation method for quantifying the superimposed impact of river and lake topography changes on lake water levels, which can provide a scientific basis for the cause analysis and quantitative evaluation of floods and droughts, as well as the ecological and environmental impact assessment. Background Art

[0002] Lakes and the rivers connected to them form a large river-lake system. The topographic trend of the river-lake system determines the relationship between rivers and lakes and the water conditions of lakes. Affected by river scouring and siltation, human activities, etc., the river-lake system undergoes topographic changes, causing the lake water level to rise or fall, increasing the risk of floods or droughts, and leading to a series of problems such as changes in water storage capacity, changes in water environment capacity, and changes in ecosystems. Quantifying changes in river-lake topography is of great significance for a deep understanding of the causes and impacts of lake floods and droughts and the formulation of corresponding policies.

[0003] The main methods for evaluating the impact of topographic changes in river and lake systems on lake water levels are statistical analysis and hydrodynamic models. Statistical analysis methods rely on long-sequence data from field measurements, but field data are often affected by multiple factors such as hydrology, topography, and water conservancy project scheduling. It is often difficult to eliminate other factors and obtain the quantitative impact of topographic changes alone. If we completely rely on hydrodynamic models to describe topographic changes in rivers and lakes, both rivers and lakes require complete DEM data of different ages, system boundary hydrological data, etc. This requires a lot of data and a large workload, which is difficult to implement in actual operations. Summary of the invention

[0004] Purpose of the invention: In view of the above-mentioned existing problems and shortcomings, the purpose of the present invention is to provide an evaluation method for quantifying the superimposed impact of river and lake topography changes on lake water levels. The present invention combines the traditional hydrodynamic model method with the water level-flow relationship method. It only requires DEMs of lakes at different ages and water level and flow sequences of major rivers at different ages to quantify the impact of topographic changes in rivers and lakes on lake water levels, providing a scientific basis for the cause analysis, quantitative evaluation and ecological environmental impact assessment of floods and droughts.

[0005] Technical solution: To achieve the above invention purpose, the present invention adopts the following technical solution: a method for quantifying the impact of river and lake topography changes on lake water level, comprising the following steps:

[0006] S1, obtain the survey year Y and the year before the terrain change Y pre The lake DEM data of the survey year is selected from the lake DEM data closest to the survey year Y, and the lake DEM data of the survey year Y before the terrain change pre The lake DEM data of the survey year Y before the lake DEM data is selected, and YY pre >5;

[0007] S2, based on the observation year Y and the year before the terrain change Y pre The lake DEM data were used to construct the survey year Y and the year before the terrain change Y pre The lake hydrodynamic model;

[0008] S3, select the flow rate of a representative station upstream of the lake in the river-lake system to represent the flow rate Q of the river, and select the water level at the lake outlet to represent the water level H at the lake outlet out , and the lake outlet water level H is calculated by logarithmic function out By fitting with the flow rate Q of the large river, we can get the Y of the survey year and Y of the year before the terrain change. pre The water level-discharge relationship function;

[0009] S4, taking the measured river flow Q in the investigation year Y as input, and based on the water level-flow relationship function and the lake hydrodynamic model of step S3, respectively calculate the lake water level before and after the river and lake topography changes, and then obtain the water level difference in the lake before and after the river and lake system topography changes.

[0010] Furthermore, the lake hydrodynamic model in step S2 is as shown in the following formula (1):

[0011] (1)

[0012] In the formula, For time; , are the horizontal and vertical coordinates in the Cartesian coordinate system respectively; , express , The average flow velocity along the water depth in the direction; H is the water level; h is the total water depth; f is the Coriolis force coefficient, , is the angular velocity of the Earth's rotation, is the local latitude; g is the acceleration due to gravity; is the water density; is the reference density of water; is the surface air pressure; , They are , Directional surface wind stress; , They are , Bottom stress in direction; , , are the three components of the horizontal viscous stress term.

[0013] Furthermore, the survey year Y and the year before the terrain change Y in step S3 preThe water level-discharge relationship function is shown in the following equations (2) and (3):

[0014] (2)

[0015] (3)

[0016] In the formula, Q pre Indicates the terrain change year before Y pre Q represents the measured flow of the major river in the survey year Y, H represents the measured flow of the major river in the survey year Y, out represents the lake outlet water level in the survey year Y, H out-pre Indicates the terrain change year before Y pre The lake outlet water level, a1, a2, b1, b2 are all fitting coefficients.

[0017] Furthermore, Poyang Lake was taken as the research object, and the discharge of Hankou upstream of Poyang Lake was used as the representative station discharge to represent the flow Q of the river. The survey year and the year before the terrain change were 2010 and 1998 respectively. The fitted water level-discharge relationship function is shown below:

[0018] .

[0019] Furthermore, in step S4, the process of obtaining the lake water level before and after the lake and river terrain changes is as follows:

[0020] First, the measured river flow Q in the survey year Y is used as the input, and the lake outlet water level H in the survey year is obtained through formula (2): out-pre Then, the lake water level H before the change of the river-lake system topography is obtained by the lake hydrodynamic model before the change of the river-lake system topography in-pre ;

[0021] Then, the measured river flow Q in the survey year Y is used as the input, and the lake outlet water level H in the survey year is obtained through formula (3): out Then, the lake water level H in the lake of the river-lake system survey year Y is obtained through the lake hydrodynamic model of the river-lake system survey year Y. in ;

[0022] Finally, ΔH=H in-pre -H in The difference in water level in the lake before and after the changes in the river-lake system.

[0023] Beneficial effects: Compared with the prior art, the present invention quantitatively evaluates the impact of the combined effects of river topography changes and lake topography changes on lake water levels based on hydrodynamic models and water level-flow relationship curves; the present invention only requires DEMs of lakes at different ages and water level and flow sequences of rivers at different ages to quantify the impact of topographic changes in rivers and lakes on lake water levels, providing a scientific basis for the cause analysis, quantitative evaluation and ecological environmental impact assessment of floods and droughts; the evaluation method of the present invention has the advantages of being quantitative, objective, concise and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a model flow of the evaluation method of the present invention;

[0025] Figure 2 A diagram showing the relationship between the flow rate from a large river and the water level out of a lake in an embodiment of the present invention;

[0026] Figure 3 A diagram showing the lake water level change process before and after the river and lake system changes in reference year Y in an embodiment of the present invention;

[0027] Figure 4 The comparison of the influence of river and lake terrain changes on the lake water level in the reference year Y in the embodiment of the present invention and the influence of only the river terrain changes and lake terrain changes on the lake water level in the reference year Y is shown in FIG.

[0028] Figure 5 It is a fitting curve of the water level change value of a certain point in the lake under the influence of the change of the river and lake terrain in the embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0030] The purpose of the present invention is to construct an evaluation method for quantifying the superimposed impact of changes in river and lake topography on lake water levels in a river and lake system where both river and lake topography have changed, and to construct a fast calculation method for the effect of changes in river and lake topography on lake water level changes (increase or decrease). The present invention can quickly and accurately quantify the contribution of changes in river and lake topography to lake low water levels or flood relief, and can solve the problems of large workload and difficulty in quantification in traditional methods, and provide scientific and technological support for flood and drought assessment, ecological environmental impact assessment, etc. in river and lake systems.

[0031] Combination Figure 1 The technical ideas and processes of the method of the present invention are described in detail below:

[0032] (1) Acquisition and processing of lake DEM data

[0033] This method targets lakes in the river-lake system and the large rivers connected to them, and based on the hydrodynamic model and the water level-discharge relationship, inverts the hydrodynamic process under different terrain conditions, and quantifies the impact of the combined changes in the topography of the large rivers and lakes on the lake water level. Figure 1 ).

[0034] After the survey year Y is determined, the year before the topography of the river system changes is Y pre , obtain the survey year Y and the year before the terrain change Y pre The hydrological data of the river and lake system is recorded every year, while the lake DEM data is updated only every ten years. Therefore, the lake DEM data of the survey year in this invention selects the lake DEM data closest to the survey year Y, and the lake DEM data of the year Y before the terrain change is selected. pre The lake DEM data of the lake before the investigation year Y was selected as the lake DEM data with no topographic changes.

[0035] (2) Construction of lake hydrodynamic model in river-lake system

[0036] Before collecting the terrain changes, Y pre The lake DEMs of year Y and year Y (i.e., the survey year) after the change were constructed based on Y pre The mathematical model of lake hydrodynamics based on the DEM of 2017 and 2018, and the equations of the lake hydrodynamic model are as follows:

[0037] (1)

[0038] In the formula, For time; , are the horizontal and vertical coordinates in the Cartesian coordinate system respectively; , express , The average flow velocity along the water depth in the direction; H is the water level; h is the total water depth; f is the Coriolis force coefficient, , is the angular velocity of the Earth's rotation, is the local latitude; g is the acceleration due to gravity; is the water density; is the reference density of water; is the surface air pressure; , They are , Directional surface wind stress; , They are , Bottom stress in direction; , , are the three components of the horizontal viscous stress term.

[0039] The hydrodynamic model has two types of open boundary condition inputs: the input of the basin's inflow into the lake, which serves as the upstream open boundary condition of the model and characterizes the lake-basin interaction relationship; the input of the water level process at the confluence of the lake and the river, which serves as the downstream open boundary condition and characterizes the river-lake interaction relationship.

[0040] Based on Lake Y pre The steps of constructing the hydrodynamic mathematical model of the DEM of year 2 and year y are as follows: First, the grid of the calculation area is discretized and the input of lake y and y are respectively pre The grids are interpolated based on the DEM of year 2 and year y; the model parameters are calibrated and verified to achieve better simulation accuracy.

[0041] After constructing the lake hydrodynamic mathematical model of DEMs of different ages, models of different ages can be selected for simulation calculations as needed. According to the hydrological year that needs to be investigated and calculated, the measured flow into the lake from the upstream and the water level at the lake outlet in that year are input, and the internal water level H of the lake area can be obtained through model calculation (either a single point water level or a multi-point water level in space).

[0042] (3) Construction of the fitting relationship between the inflow of large rivers and the outflow water level of lakes in the river-lake system

[0043] For large rivers, under stable riverbed conditions, the river water level and upstream flow rate show a stable and highly correlated relationship. However, due to silt scouring, engineering impacts and other reasons, the riverbed topography will change to a certain extent, thus causing changes in the water level-flow relationship.

[0044] The present invention selects the flow rate Q of a representative station in the upper reaches of a river in the river-lake system to represent the flow rate of the river; selects the water level H at the lake outlet out (lake-river junction, also at the lake outlet boundary), represents the lake outlet water level. Lake outlet water level H out There is a good correlation with the flow Q of the representative station in the upper reaches of the river. The present invention adopts a logarithmic function for fitting, such as Figure 2 shown.

[0045] Before the change of the Dajiang terrain pre Year (1998): Based on Y pre The measured flow rate of the river in 2018 is Q pre , the measured water level at the lake outlet H out-pre , fitting H out-pre -Q pre The water level-flow relationship curve is used to obtain the Y before the river terrain changes. preThe annual water level-flow relationship is (2), R 2 Both can reach 0.97.

[0046] H out-pre = 6.38ln(Q pre ) - 48.9 (2)

[0047] Year Y after the topography of the major rivers changed (i.e., survey year Y, 2010): based on the measured flow Q of the major rivers in year Y and the measured water level H at the lake outlet out , fitting H out -Q water level flow relationship curve, we can get the water level flow relationship formula (3) in year Y after the topography of the river changes. 2 It can reach 0.97.

[0048] H out = 6.96ln(Q) - 55.5 (3)

[0049] (4) Quantification of the impact of topographic changes in river and lake systems on lake water levels

[0050] The topographic changes of the river and lake system refer to the topographic changes of lakes superimposed on the topographic changes of large rivers. Based on the topography before and after the changes in the river and lake topography, the water conditions in the same survey year Y are calculated and the differences in lake water levels are compared. The specific steps are as follows:

[0051] ① Lake level before the topography of the river-lake system changes: the measured river flow Q in year Y y Substitute into formula (2) and calculate the lake outlet water level H Y years before the river topography changes out-pre , then calculate the H out-pre The hydrodynamic model before the lake topography change (Y pre 2017 lake DEM), the lake water level H in 2017 before the lake-river system topography changes can be calculated. in-pre ;

[0052] ② Lake level after the topography of the river-lake system changes: the measured river flow Q in year Y y Substitute into formula (3) and calculate the lake outlet water level H in year Y after the topography of the river changes. out , then calculate the H out By introducing the hydrodynamic model after the lake topography changes (the DEM of the lake in year Y investigated), the water level H in the lake in year Y after the lake-river system topography changes can be calculated. in ;

[0053] ③ Quantify the impact of river and lake topography on water level: compare the difference in water level before and after the change in the river and lake topography (ΔH = H in-pre -H in ), the impact of topographic changes on the river and lake system can be quantified.

[0054] The lake water levels before and after the changes in river and lake terrain calculated based on the above method are shown in Figure 2. Figure 3 shown.

[0055] In addition to quantifying the impact of topographic changes on the river and lake system, the evaluation method of the present invention can also separately calculate the topographic changes of major rivers and lakes. The present invention is described as follows:

[0056] Quantification of the impact of topographic changes of individual major rivers: Using the same lake DEM in steps ① and ② above, and repeating steps ① to ③, the impact of topographic changes of major rivers on lake water levels can be quantified.

[0057] Quantification of the impact of changes in lake topography: Use the same lake outlet water level (measured value, or calculated using the same formula) in steps ① and ②, and repeat steps ① to ③ to quantify the impact of lake topography changes on lake water levels.

[0058] The impact of the terrain changes of the river and lake system on the water level is compared with that of the terrain changes of only the major rivers and lakes. Figure 4 As shown (monthly scale). From the perspective of monthly average (or daily), the magnitude and time period of the impact of river changes, lake changes, and the superposition of the two on the water level can be compared. In general, the impact of river and lake topography changes on lake levels is less than the sum of the impacts of river and lake changes alone, showing nonlinear changes.

[0059] Based on the water level calculation results, the impact of river and lake topography changes on lake water levels was further fitted ( Figure 5 ), the fitting formula is shown in formula (4):

[0060] ΔH = 189.77H in -2 (4)

[0061] H in is the measured value of the water level at a certain point in the existing lake, and ΔH is the water level change value caused by the change of the river and lake topography at that point. Based on this formula, the water level change caused by the change of the river and lake system topography under a specific lake water level condition can be quickly deduced, which is conducive to the attribution analysis of lake water level changes.

Claims

1. A method for quantifying the impact of changes in river and lake topography on lake water levels, characterized in that The following steps are involved: S1, obtain the survey year Y and the year before the terrain change Y pre The lake DEM data of the survey year is selected from the lake DEM data closest to the survey year Y, and the lake DEM data of the survey year Y before the terrain change pre The lake DEM data of the survey year Y before the lake DEM data is selected, and YY pre >5; S2, based on the observation year Y and the year before the terrain change Y pre The lake DEM data were used to construct the survey year Y and the year before the terrain change Y pre The lake hydrodynamic model; S3, select the flow rate of a representative station upstream of the lake in the river-lake system to represent the flow rate Q of the river, and select the water level at the lake outlet to represent the water level H at the lake outlet out , and the lake outlet water level H is calculated by logarithmic function out By fitting with the flow rate Q of the large river, we can get the Y of the survey year and Y of the year before the terrain change. pre The water level-discharge relationship function; S4, taking the measured river flow Q in the investigation year Y as input, and based on the water level-flow relationship function of step S3 and the lake hydrodynamic model described in step S2, respectively calculate the lake water level before and after the river and lake topography changes, and then obtain the water level difference in the lake before and after the river and lake system topography changes.

2. The method for evaluating the impact of changes in river and lake topography on lake water levels according to claim 1 is characterized by: The lake hydrodynamic model in step S2 is as shown in equation (1): （1） In the formula, For time; , are the horizontal and vertical coordinates in the Cartesian coordinate system respectively; , express , The average flow velocity along the water depth in the direction; H is the water level; h is the total water depth; f is the Coriolis force coefficient, , is the angular velocity of the Earth's rotation, is the local latitude; g is the acceleration due to gravity; is the water density; is the reference density of water; is the surface air pressure; , They are , Directional surface wind stress; , They are , Bottom stress in direction; , , are the three components of the horizontal viscous stress term.

3. The method for evaluating the impact of changes in river and lake topography on lake water levels according to claim 1 is characterized by: The survey year Y and the year before the terrain change Y in step S3 pre The water level-discharge relationship function is shown in the following equations (2) and (3): （2） （3） In the formula, Q pre Indicates the terrain change year before Y pre Q represents the measured flow of the major river in the survey year Y, H represents the measured flow of the major river in the survey year Y, out represents the lake outlet water level in the survey year Y, H out-pre Indicates the terrain change year before Y pre The lake outlet water level, a1, a2, b1, b2 are all fitting coefficients.

4. The method for evaluating the impact of changes in river and lake topography on lake water levels according to claim 3 is characterized by: Poyang Lake was taken as the research object, and the discharge of Hankou upstream of Poyang Lake was used as the representative station discharge to represent the flow Q of the river. The survey year and the year before the terrain change were 2010 and 1998 respectively. The fitted water level-discharge relationship function is shown below: 。 5. The method for evaluating the quantified impact of river and lake topography changes on lake water levels according to claim 3 is characterized by: The process of obtaining the lake water level before and after the lake and river terrain changes in step S4 is as follows: First, the measured river discharge Q in the survey year Y is used as the input, and the lake outlet water level H in the survey year before the topographic change is obtained through formula (2): out-pre Then, the lake water level H before the change of the river-lake system topography is obtained by the lake hydrodynamic model before the change of the river-lake system topography in-pre ; Then, the measured river flow Q in the survey year Y is used as the input, and the lake outlet water level H in the survey year is obtained through formula (3): out Then, the lake water level H in the lake of the river-lake system survey year Y is obtained through the lake hydrodynamic model of the river-lake system survey year Y. in ; Finally, ΔH=H in-pre -H in The difference in water level in the lake before and after the changes in the river-lake system.

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