Method for defining critical hydrodynamic environment for benthic organism passive migration

Abstract

The application discloses a method for defining a critical hydrodynamic environment of passive migration of benthos, and belongs to the technical field of hydraulic engineering. The method comprises the following steps: burying a wide-mouth slot sampler in a preselected research area where passive migration of benthos occurs; determining a test time based on the average distribution width and the average migration speed of the benthos population in the research area; taking out the wide-mouth slot sampler when the test time is up, and weighing and measuring the volume of the collected benthos to calculate the migration rate and individual density of the benthos; repeating the test at different positions of the preselected research area where passive migration of benthos occurs to obtain a plurality of test data; calculating the undetermined parameters in a pre-constructed parameter determination model according to the plurality of test data, and calculating the critical hydrodynamic environment of passive migration of benthos due to exposure according to the undetermined parameters. The method can accurately define the critical hydrodynamic environment of passive migration of benthos due to exposure.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for defining the critical hydrodynamic environment of passive migration of benthos, and belongs to the technical field of hydraulic engineering. BACKGROUND

[0002] The migration of benthos mainly involves two aspects, namely active migration and passive migration.

[0003] Active migration is often the autonomous migration of benthos, that is, benthos relies on its own action ability to migrate for a short or long distance. This process may be affected by external changes in the living environment, or by the survival and development needs of benthos individuals or populations.

[0004] Passive migration is the non-autonomous passive migration of benthos, that is, the natural environment of the benthos living area changes, causing the benthos to be exposed to the bed surface, and then subjected to the impact of the external hydrodynamic environment to form the migration of individuals or populations. For example, the bed surface is significantly eroded in a short period of time, causing a significant decrease in the bed surface elevation, causing the benthos to be passively exposed to the bed surface, and then directly subjected to the impact of the surrounding water power to migrate. For example, the bed surface properties decrease the air permeability due to external environmental reasons, causing the benthos to no longer be suitable for long-term survival under the bed surface, causing the benthos to actively climb out of the habitat cave and be exposed to the bed surface, and then directly subjected to the impact of the surrounding water power to migrate.

[0005] Due to the exposure of benthos to the bed surface, under the direct impact of the external hydrodynamic environment, it is extremely likely that the benthos will be carried away by the water flow and leave the original habitat, thereby causing the migration of benthos individuals or populations. However, due to the particularity of the benthos living environment and the complexity of the benthos type, it is difficult to accurately define the critical hydrodynamic environment for passive migration of benthos.

[0006] In summary, there is a need for a method that can accurately define the critical hydrodynamic environment for passive migration of benthos due to exposure, in order to accurately assess the likelihood of passive migration of benthos on the bed surface. SUMMARY

[0007] The purpose of the present application is to provide a method for defining the critical hydrodynamic environment of passive migration of benthos, which can accurately define the critical hydrodynamic environment for passive migration of benthos due to exposure.

[0008] To achieve the above purpose, the present application provides the following technical solution:

[0009] A method for defining the critical hydrodynamic environment of passive migration of benthos, comprising:

[0010] Wide-mouth trough samplers were installed in the pre-selected study area where benthic organisms showed passive migration.

[0011] The test time was determined based on the average distribution width and average migration speed of benthic populations in the study area.

[0012] Once the testing time has ended, remove the wide-mouth trough sampler and weigh and measure the volume of the collected benthic organisms to calculate the migration rate and individual density of the benthic organisms.

[0013] The test was repeated at different locations in the pre-selected study area where benthic organisms exhibited passive migration, and several test data were obtained.

[0014] Based on several test data, pre-constructed parameters are calculated to determine the undetermined parameters in the model, and the critical hydrodynamic environment for the passive migration of benthic organisms due to exposure is calculated based on the undetermined parameters.

[0015] Furthermore, wide-mouth trough samplers were installed in the pre-selected study areas where passive migration of benthic organisms was observed, including:

[0016] Downstream of the passive migration of benthic organisms, wide-mouth trough-type samplers are buried along the direction perpendicular to the shoreline and perpendicular to the migration direction of benthic organisms.

[0017] Clean the exposed benthic organisms at the leading edge of the wide-mouth trough sampler and level the bed surface;

[0018] Open the top cover of the wide-mouth slot sampler and adjust the burial depth of the wide-mouth slot sampler so that the top height of the leading edge of the wide-mouth slot sampler is lower than the top height of the flat bed surface.

[0019] Furthermore, the distance between the top height of the leading edge of the wide-mouth trough sampler and the top height of the flat bed surface is determined based on the local bed erosion rate and the time of this test. The formula for calculating the distance between the top height of the leading edge of the wide-mouth trough sampler and the top height of the flat bed surface is as follows:

[0020] Δ=E×T

[0021] Where Δ is the distance between the top height of the leading edge of the wide-mouth slot sampler and the top height of the flat bed surface, E is the bed erosion rate, and T is the test time.

[0022] Furthermore, the formula for calculating the test time is:

[0023] T = L / U

[0024] Where T is the test time, L is the average distribution width of the benthic population, and U is the average migration speed of the benthic organisms during passive migration.

[0025] Furthermore, the formulas for calculating the migration rate and individual density of benthic organisms are as follows:

[0026]

[0027] wherein G is the migration rate of benthos, p is the individual density of benthos, W is the total mass of benthos collected by the wide-mouthed slot sampler, T is the test time, and V is the total volume of benthos collected by the wide-mouthed slot sampler. D

[0028] Further, the parameter determination model is:

[0029]

[0030] wherein G is the migration rate of benthos, p is the individual density of benthos, p is the density of water, g is the acceleration of gravity, D is the equivalent diameter of benthos individual, h is the water depth, t is the shear stress of water flow, and a, b, and c are undetermined parameters of the parameter determination model. D

[0031] Further, the equivalent diameter of benthos individual is obtained by:

[0032] measuring the individual volume of the collected benthos;

[0033] performing weighted average on the individual volume of the measured benthos to obtain the arithmetic mean volume of benthos;

[0034] taking the diameter of the sphere with the same volume as the arithmetic mean volume of benthos as the equivalent diameter of benthos individual.

[0035] Further, the calculation formula of the critical hydrodynamic environment of passive migration of benthos due to exposure is:

[0036]

[0037] wherein t is the critical hydrodynamic environment of passive migration of benthos due to exposure, p is the individual density of benthos, p is the density of water, g is the acceleration of gravity, D is the equivalent diameter of benthos individual, h is the water depth, t is the shear stress of water flow, a, b, and c are undetermined parameters of the parameter determination model, and GD is the trace migration rate of benthos. D D

[0038] Further, the trace migration rate of benthos is calculated according to the minimum value of the individual mass of the collected benthos, and the calculation formula of the trace migration rate of benthos is:

[0039] G D = W min / T / 2

[0040] wherein W​​​​min T is the test time.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] The present application provides a method for defining the critical hydrodynamic environment of passive migration of benthic organisms, which directly calculates the critical shear stress of passive migration of benthic organisms according to the parameters of benthic organism individual density, equivalent diameter, water shear stress, passive migration rate of benthic organisms obtained by field monitoring and laboratory testing, thereby solving the problem that the loss of benthic organisms on the bed surface caused by passive migration of benthic organisms in the intertidal zone of the coast is difficult to directly evaluate, monitor and accurately calculate. In the intertidal zone, the method can effectively evaluate the influence of the natural environment change caused by the coastal engineering on the natural survival and development of the benthic organisms in the intertidal zone of the coast in combination with the coastal hydrodynamic environment and the type of benthic organism community, and further can correct the corresponding engineering scheme, and has strong practicability and wide applicability. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a flowchart of the method for defining the critical hydrodynamic environment of passive migration of benthic organisms provided by the present application;

[0044] Figure 2 is a schematic diagram of the arrangement of the wide-mouthed slot sampler provided by the present application. DETAILED DESCRIPTION

[0045] The technical solutions of the present application will be further described in detail below with reference to the specific embodiments.

[0046] The embodiments of the present application will be described in detail below, and examples of the embodiments are shown in the drawings, in which the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation on the present application. The technical features in the embodiments of the present application and the embodiments can be combined with each other without conflict.

[0047] Embodiment 1:

[0048] Figure 1 is a flowchart of the method for defining the critical hydrodynamic environment of passive migration of benthic organisms provided by the present application, and the flowchart only shows the logical order of the method of the present embodiment, and the steps shown or described can be completed in an order different from that shown in the present embodiment without conflict. Figure 1

[0049] Referring to Figure 1 , the method of the present embodiment specifically includes the following steps:

[0050] ​Step one: burying wide-mouthed groove type samplers in the pre-selected research area where passive migration of benthos occurs;

[0051] Burying wide-mouthed groove type samplers in the pre-selected research area where passive migration of benthos occurs includes the following steps:

[0052] Step 1: burying wide-mouthed groove type samplers on the downstream side of passive migration of benthos along the direction perpendicular to the shoreline and the direction perpendicular to the migration direction of benthos;

[0053] In this embodiment, wide-mouthed groove type samplers with a length of 2m, a width of 0.3m and a depth of 0.5m are buried on the downstream side of passive migration of benthos along the direction perpendicular to the shoreline and the direction perpendicular to the migration direction of benthos.

[0054] Step 2: cleaning exposed benthos on the front edge of the wide-mouthed groove type sampler and flattening the bed surface;

[0055] In this embodiment, exposed benthos within a range of 0.2m on the front edge (opposite to the passive migration direction of benthos) of the wide-mouthed groove type sampler is cleaned and the bed surface is flattened before the test begins.

[0056] Step 3: opening the top cover of the wide-mouthed groove type sampler and adjusting the burial depth of the wide-mouthed groove type sampler so that the top height of the front edge of the wide-mouthed groove type sampler is lower than the top height of the flattened bed surface.

[0057] In this embodiment, the top cover of the wide-mouthed groove type sampler is opened and the burial depth of the wide-mouthed groove type sampler is adjusted so that the top height of the front edge of the wide-mouthed groove type sampler is lower than the top height of the flattened bed surface, so that the wide-mouthed groove type sampler can smoothly collect the passively migrating benthos during the entire test time.

[0058] The distance by which the top height of the front edge of the wide-mouthed groove type sampler is lower than the top height of the flattened bed surface is determined according to the local bed surface erosion rate and the test time, and the calculation formula of the distance by which the top height of the front edge of the wide-mouthed groove type sampler is lower than the top height of the flattened bed surface is:

[0059] Δ=E×T

[0060] Wherein, Δ is the distance by which the top height of the front edge of the wide-mouthed groove type sampler is lower than the top height of the flattened bed surface, E is the bed surface erosion rate, and T is the test time.

[0061] Step two: determining the test time based on the average distribution width and the average migration speed of the benthos population in the research area;

[0062] The calculation formula of the test time is:

[0063] T=L / U

[0064] Wherein, T is the test time, L is the average distribution width of the benthos population, and U is the average migration speed of passive migration of benthos.

[0065] In this embodiment, when the parameters of the average distribution width of benthic populations and the average migration speed of passive migration are lacking, the testing time T is often required to satisfy 1 day < T < 3 days in order to simplify the testing workload.

[0066] Step 3: After the test time expires, take out the wide-mouth trough sampler, weigh and measure the volume of the collected benthic organisms, and calculate the migration rate and individual density of the benthic organisms.

[0067] In this embodiment, after the test time expires, the wide-mouth trough sampler is covered with a top cover and brought back to the laboratory. The benthic organisms collected in the wide-mouth trough sampler are cleaned, weighed, and their volume is measured. The migration rate and individual density of the benthic organisms are calculated based on the test time.

[0068] The formulas for calculating the migration rate and individual density of benthic organisms are as follows:

[0069]

[0070] Where G is the migration rate of benthic organisms, ρ D denoted as the individual density of benthic organisms, W as the total mass of benthic organisms collected by the wide-mouth trough sampler, T as the test time, and V as the total volume of benthic organisms collected by the wide-mouth trough sampler.

[0071] Step 4: Repeat the test at different locations in the pre-selected study area where benthic organisms exhibited passive migration, and obtain a number of test data;

[0072] In this embodiment, another location within the same study area is selected, which must be more than 200m away from the previous test area. Steps one through four are repeated, and the test is repeated at least six times to obtain at least seven sets of test data.

[0073] like Figure 2 The diagram shown is a schematic of the arrangement of a wide-mouth slot sampler. Figure 2 In this context, L1 to L7 represent the distances between the seven wide-mouth slot samplers in the seven tests, and the distance between L1 and L7 is not less than 200m.

[0074] Step 5: Calculate and obtain the pre-constructed parameters based on several test data to determine the undetermined parameters in the model, and calculate and obtain the critical hydrodynamic environment for the passive migration of benthic organisms due to exposure based on the undetermined parameters.

[0075] In this embodiment, based on several test data, the least squares method is used to calculate and obtain the undetermined parameters in the pre-constructed parameter determination model, and the critical hydrodynamic environment for the passive migration of benthic organisms due to exposure is calculated based on the undetermined parameters.

[0076] The parameter determination model is:

[0077]

[0078] Wherein, G is the migration rate of benthic organism, p D is the individual density of benthic organism, p is the density of water, g is the acceleration of gravity, D is the equivalent diameter of benthic organism individual, h is the water depth, tau is the shear stress of water flow, a, b, c are the undetermined parameters of the parameter determination model.

[0079] The equivalent diameter of benthic organism individual includes the following steps:

[0080] Step (1): measuring the individual volume of the collected benthic organism;

[0081] Step (2): weighted average of the measured individual volume of benthic organism, to obtain the arithmetic mean volume of benthic organism;

[0082] Step (3): the diameter of the equivalent volume sphere of the arithmetic mean volume of benthic organism is taken as the equivalent diameter of benthic organism individual.

[0083] The calculation formula of the critical hydrodynamic environment of passive migration of benthic organism due to exposure is:

[0084]

[0085] Wherein, tau D is the critical hydrodynamic environment of passive migration of benthic organism due to exposure, p D is the individual density of benthic organism, p is the density of water, g is the acceleration of gravity, D is the equivalent diameter of benthic organism individual, h is the water depth, tau is the shear stress of water flow, a, b, c are the undetermined parameters of the parameter determination model, G D is the trace migration rate of benthic organism.

[0086] The trace migration rate of benthic organism is calculated according to the minimum value of the individual mass of the collected benthic organism, and the calculation formula of the trace migration rate of benthic organism is:

[0087] G D = W min / T / 2

[0088] Wherein, W min is the minimum value of the individual mass of the collected benthic organism, T is the test time.

[0089] The method for defining the critical hydrodynamic environment of passive migration of benthic organisms provided by the embodiment directly calculates the critical shear stress of passive migration of benthic organisms according to the parameters of individual density of benthic organisms, equivalent diameter, water shear stress, passive migration rate of benthic organisms obtained through field monitoring and laboratory tests, and solves the problem that the loss of benthic biomass on the bed surface caused by passive migration of benthic organisms in the intertidal zone of the coast is difficult to directly evaluate, monitor and accurately calculate. In the intertidal zone, the method can effectively evaluate the influence of the natural environment change caused by the coastal engineering on the natural survival and development of the benthic organisms in the intertidal zone of the coast in combination with the coastal hydrodynamic environment and the type of benthic community, and then the corresponding engineering scheme can be corrected, and the method has strong practicability and wide applicability.

[0090] The above is only the preferred embodiment of the present application, and it should be pointed out that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications should be considered as the protection scope of the present application.

Claims

1. A method of defining a critical hydrodynamic environment for benthic organism passive migration, characterized by, The application relates to a method for determining the critical hydrodynamic environment of passive migration of benthos. The method comprises the following steps: embedding a broad-mouth slot sampler in a research area where passive migration of benthos occurs; determining a test time based on the average distribution width and average migration speed of the benthos population in the research area; removing the broad-mouth slot sampler and weighing and measuring the volume of the collected benthos to calculate the migration rate and individual density of the benthos when the test time is up; repeating the test in different positions of the research area where passive migration of benthos occurs to obtain several test data; calculating the undetermined parameters in a pre-constructed parameter determination model based on the several test data, and calculating the critical hydrodynamic environment of passive migration of benthos due to exposure based on the undetermined parameters; ； wherein, is the mobility of the benthos, is the individual density of the benthos, is the water density, is the gravitational acceleration, is the equivalent diameter of the benthos individual, is the water depth, is the shear stress of the water flow, , , is a parameter to be determined by the model of the parameter determination model; the parameter determination model is as follows: ； wherein, a critical hydrodynamic environment for passive migration of benthic organisms due to exposure, a density of benthic organisms, a density of water, a gravitational acceleration, an equivalent diameter of a benthic organism, a water depth, a shear stress of a water flow, , , a pending parameter for a parameter determination model, a micro-mobility of benthic organisms; the calculation formula of the critical hydrodynamic environment of passive migration of benthos due to exposure is as follows: ； wherein, is the minimum value of the individual mass of the collected benthos, is the test time.

2. The method for defining the critical hydrodynamic environment for passive migration of benthic organisms according to claim 1, characterized in that, the trace migration rate of the benthos is calculated based on the minimum value of the individual mass of the collected benthos, and the calculation formula of the trace migration rate of the benthos is as follows: embedding a broad-mouth slot sampler in a research area where passive migration of benthos occurs comprises the following steps: embedding the broad-mouth slot sampler on the downstream side of passive migration of benthos along the direction perpendicular to the shoreline and the direction perpendicular to the migration direction of the benthos; cleaning the exposed benthos in the front edge of the broad-mouth slot sampler and flattening the bed surface; 3. The method of claim 2, wherein the critical hydrodynamic environment is defined by a critical velocity (Uc) and a critical length scale (Lc) such that: Lc = Uc / U* where U* is a friction velocity. opening the top cover of the broad-mouth slot sampler, adjusting the embedding depth of the broad-mouth slot sampler, and making the top height of the front edge of the broad-mouth slot sampler lower than the top height of the flattened bed surface. ； wherein, is the distance of the top of the leading edge of the wide-slot sampler below the top of the flat bed surface, is the bed surface erosion rate, is the test time.

4. The method for defining the critical hydrodynamic environment for passive migration of benthic organisms according to claim 1, characterized in that, The distance between the top height of the front edge of the broad-mouth slot sampler and the top height of the flattened bed surface is determined based on the local bed surface erosion rate and the test time, and the calculation formula of the distance is as follows: ； wherein, is the test time, is the average distribution width of the benthic organism population, is the average migration speed of the passive migration of the benthic organism.

5. The method for defining the critical hydrodynamic environment for passive migration of benthic organisms according to claim 1, characterized in that, the calculation formula of the test time is as follows: ； wherein, is the migration rate of the benthos, is the individual density of the benthos, is the total mass of the benthos collected by the wide-mouthed slot sampler, is the test time, is the total volume of the benthos collected by the wide-mouthed slot sampler.

6. The method of claim 1, wherein the method is a method of defining a critical hydrodynamic environment for benthic organism passive migration, further comprising: the calculation formula of the migration rate and individual density of the benthos is as follows: obtaining the equivalent diameter of the benthos individual comprises the following steps: measuring the individual volume of the collected benthos; performing weighted average on the measured individual volume of the benthos to obtain the arithmetic average volume of the benthos; taking the diameter of the equivalent volume sphere of the arithmetic average volume of the benthos as the equivalent diameter of the benthos individual.

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