Method and system for calculating coastal sand transportation of sandy coast

Abstract

The invention relates to the technical field of coastal engineering, and discloses a coastal sand transport calculation method and system for a sandy coast, and the method comprises the following steps: obtaining target parameters and initial profile data of a target coast; calculating a profile change item caused by transverse sediment transport through a one-dimensional beach evolution model; an equivalent coastal distance parameter is innovatively introduced, and the coastal sediment transport gradient is rapidly estimated; calculating an elevation change item caused by coastal sediment transportation in combination with the gradient; overlapping transverse and coastal change items to obtain complete bed elevation evolution data; iteratively calibrating the equivalent coastline distance parameter based on historical terrain data until the simulation result conforms to the actually measured shoreline change; and finally outputting the calibrated coastal sediment transportation influence prediction. And the problem of prediction deviation caused by neglecting the coastal sediment transport gradient of a traditional one-dimensional beach evolution model can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coastal engineering, and particularly relates to a method and system for calculating alongshore sediment transport of sandy coast. BACKGROUND

[0002] Sandy coast is an important area of interaction between the ocean and the land, which is influenced by wave, tidal current and other dynamic factors, and the morphology of the coastline and the nearshore bed continues to dynamically evolve. The evolution process of the sandy coast is mainly driven by wave, flow and sediment transport, and the prediction accuracy is crucial to the design of coastal protection projects. Traditional one-dimensional beach evolution models (such as the CSHORE model) are based on the continuity equation of the bed sediment, focusing on the transverse sediment transport process, i.e. simulating the sediment transport perpendicular to the coastline (such as onshore-offshore movement). Such one-dimensional beach evolution models assume that the volume of erosion area is equal to the volume of deposition area (i.e. the "local conservation" assumption) within the range from the land boundary to the closed depth under water. However, actual observations show that most sandy coasts have a persistent coastline recession phenomenon (the erosion volume is significantly greater than the deposition volume), and the coupling relationship between the cross-section elevation change and the alongshore sediment transport is still insufficient. Especially when dealing with non-uniform coastlines or variable topography conditions, the conventional method often ignores the influence of spatial differences in alongshore sediment transport on profile evolution, resulting in limited simulation accuracy.

[0003] Although two-dimensional numerical models can simulate the alongshore sediment transport gradient, they need to couple wave, flow, sediment transport and other multi-physical field equations, which takes a long time to calculate (usually several hours to several days), and the time cost is relatively high, which makes it difficult to meet the demand for rapid evaluation and multi-working condition iteration in the preliminary design stage of the project.

[0004] Therefore, there is an urgent need for a method for calculating alongshore sediment transport of sandy coast, which can comprehensively reflect the coupling effect of transverse and longitudinal sediment transport, improve the calculation efficiency, and improve the accuracy of sandy coast evolution simulation. SUMMARY

[0005] To solve the above technical problems, the present application provides a method for calculating alongshore sediment transport of sandy coast, which has the advantages of high calculation efficiency, strong adaptability, simple structure, etc., and is particularly suitable for long time series, multi-working condition sandy beach response prediction and structural optimization design research.

[0006] The present application provides a method for calculating alongshore sediment transport of sandy coast, comprising the following steps: S1, obtaining the basic parameters and initial profile of the target coast; S2, inputting the basic parameters and initial profile into a one-dimensional beach evolution model to obtain a transverse profile change term caused by alongshore sediment transport of the target coast; The one-dimensional beach evolution model is a CSHORE model; S3, introducing an equivalent alongshore distance parameter to calculate the alongshore sediment transport gradient; S4, determining the initial value of the equivalent alongshore distance parameter, inputting the alongshore sediment transport gradient into a one-dimensional beach evolution model to calculate the alongshore elevation change item caused by the alongshore sediment transport of the target coast; S5, superimposing the lateral profile change item and the alongshore elevation change item to obtain the complete topographic change data of the target coast caused by the alongshore sediment transport; S6, iteratively calibrating the equivalent alongshore distance parameter based on the target coast historical topographic change data until the topographic change output by S5 has an error less than a preset threshold value from the target coast historical topographic change data; S7, inputting the calibrated equivalent alongshore distance parameter and the basic parameters and initial profile of the target coast collected in real time into the one-dimensional beach evolution model to output the topographic change data caused by the alongshore sediment transport.

[0007] Further, in S3, the formula of the equivalent alongshore distance parameter is: wherein y e represents the equivalent alongshore distance parameter, q y represents the unit width alongshore sediment transport rate, and represents the alongshore sediment transport gradient.

[0008] Further, in S1, the basic parameters include: wave incidence angle, wave height, wave period, sediment particle size, sedimentation velocity, specific gravity and bottom sediment porosity; the initial profile includes: land boundary and bottom elevation data within the range of closed depth under water, and the closed depth under water is determined by the wave breaking critical condition. Further, the initial value of the equivalent alongshore distance parameter is set as the average distance from the wave incidence boundary to the target coastline.

[0009] Further, in S4, the alongshore elevation change item is solved by the following formula: ; wherein n p represents the bottom sediment porosity; represents the alongshore elevation change amount caused by the alongshore sediment transport; represents the time interval of the simulated beach evolution; Q y represents the unit width time average volume flux in the alongshore direction, , x m is the lateral profile calculation range, q y is the unit width total alongshore sediment transport rate.

[0010] Further, S6 specifically includes: S61, collecting target coast historical topographic change data; S62, input the initial value of the equivalent alongshore distance parameter into the one-dimensional beach evolution model, execute S1-S5, and obtain complete terrain change data of the target coast caused by alongshore sediment transport; S63, adjust the equivalent alongshore distance parameter in an equivalent order, and repeat S62 until the error between the terrain change and the target coast historical terrain change data is less than a preset threshold.

[0011] Further, in S61, the target coast historical terrain change data includes shoreline translation position data, measured erosion area and deposition area values, and bottom elevation spatial distribution form data of different time periods. In S62, the terrain change data of the target coast caused by alongshore sediment transport includes simulated shoreline recession distance, simulated erosion area and deposition area, and simulated bottom elevation spatial distribution form data.

[0012] The application also provides a sandy coast alongshore sediment transport calculation system for the above-mentioned sandy coast alongshore sediment transport calculation method, which comprises: A data input module is configured to obtain basic parameters and an initial profile of a target coast. A lateral profile simulation module is configured to input the basic parameters and the initial profile into a one-dimensional beach evolution model to obtain a lateral profile change term of the target coast caused by alongshore sediment transport. An alongshore sediment transport gradient calculation module is configured to introduce an equivalent alongshore distance parameter and calculate an alongshore sediment transport gradient. An alongshore elevation simulation module is configured to determine an initial value of the equivalent alongshore distance parameter, input the alongshore sediment transport gradient into the one-dimensional beach evolution model, and calculate an alongshore elevation change term of the target coast caused by alongshore sediment transport. A terrain change acquisition module is configured to superimpose the lateral profile change term and the alongshore elevation change term to obtain complete terrain change data of the target coast caused by alongshore sediment transport. A calibration module is configured to iteratively calibrate the equivalent alongshore distance parameter based on target coast historical terrain change data until the error between the terrain change data output by the terrain change acquisition module and the target coast historical terrain change data is less than a preset threshold. A result output module is configured to input the calibrated equivalent alongshore distance parameter, real-time collected basic parameters and an initial profile of the target coast into the one-dimensional beach evolution model, and output terrain change data caused by alongshore sediment transport.

[0013] The application has the following technical effects: The application efficiently characterizes the non-uniformity of alongshore sediment transport in a one-dimensional beach evolution model by introducing an equivalent alongshore distance parameter and its calculation formula. This innovative design breaks through the physical limitations of traditional models relying on the "local conservation" assumption. Traditional methods always present a false equilibrium state with erosion area equal to deposition area due to the neglect of alongshore sediment transport gradient, which cannot explain the actual shoreline continuous recession phenomenon. The application quantifies the alongshore sediment transport gradient through the equivalent parameter, and for the first time, it reproduces the net loss process with erosion area significantly larger than deposition area in a one-dimensional framework, accurately capturing the shoreline recession trend. At the same time, based on the CSHORE model integration scheme, the model avoids the high computational cost of two-dimensional models while retaining the efficiency advantage of one-dimensional calculation, achieving the unification of rapid engineering evaluation and long-term evolution prediction. The equivalent alongshore distance parameter is dynamically optimized based on historical shoreline data, making it output reliable predictions for complex scenarios such as cliff coasts. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0015] Figure 1 is a flowchart of a sandy coast alongshore sediment transport calculation method provided by an embodiment of the present application; Figure 2 is a schematic diagram of a cliff coast topography and wave incidence provided by an embodiment of the present application; Figure 3 is a comparison diagram of the initial state of the beach profile, the calculation results of the one-dimensional beach evolution model, and the calculation results of the method provided by the present application. DETAILED DESCRIPTION

[0016] In order to make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0017] Figure 1 is a flowchart of a sandy coast alongshore sediment transport calculation method provided by an embodiment of the present application. Referring to Figure 1 , the method comprises the following steps: S1, obtaining the basic parameters and initial profile of the target coast.

[0018] In some embodiments, in the S1, the basic parameters include: wave incidence angle, wave height, wave period, sediment particle size, settling velocity, specific gravity and bottom sediment porosity; and the initial profile includes: land boundary and bottom elevation data within the range of underwater closure depth, the underwater closure depth being determined by the wave breaking critical condition. Specifically, in the process of calculating the alongshore sediment transport of a sandy coast, obtaining the basic parameters and the initial profile of the target coast is a core step of model initialization. The selection of the basic parameters needs to comprehensively reflect the coastal dynamic environment and the sediment transport characteristics: the wave incidence angle is used to quantify the component of wave energy in the alongshore direction, which directly affects the alongshore sediment transport intensity; the wave height and the wave period jointly determine the nearshore wave energy distribution, which controls the sediment starting and suspension ability; the sediment particle size reflects the sediment transport response sensitivity, coarse particles need higher starting flow velocity, and fine particles are easy to suspend and migrate; the settling velocity is related to the re-landing and deposition process of suspended sediment, which affects the beach deposition rate; the specific gravity is used for the conversion of the dense volume of sediment, and the porosity is used for the correction of the sediment volume; and the bottom sediment porosity represents the gap proportion between the sand skeletons, which is used to correct the solid volume sediment transport amount. The definition of the initial profile needs to cover the complete range from the land boundary to the underwater closure depth. The land boundary is usually bounded by the coastal vegetation line or artificial structures, and the underwater closure depth is naturally formed by the wave breaking critical condition. The depth far away from the depth, the wave energy significantly decays, and the sediment transport activity tends to be static, which constitutes the natural boundary of the transverse calculation domain.

[0019] The initial profile data is usually obtained through field topographic survey and historical data integration. The wave parameters can be inversed through observation buoys or numerical simulation (such as the SWAN model), and the sediment characteristics are determined through the surface sediment screening experiment and the settling column test.

[0020] S2, inputting the basic parameters and the initial profile into a one-dimensional beach evolution model to obtain a transverse profile variation term caused by the alongshore sediment transport of the target coast.

[0021] In some embodiments, the one-dimensional beach evolution model is the CSHORE model.

[0022] In this embodiment, after inputting the basic parameters and the initial profile into the one-dimensional beach evolution model, the model first reconstructs the nearshore wave height field distribution based on the wave refraction-diffraction theory. The wave incidence angle and the wave height parameters drive the wave propagation equation to solve, generating the spatial gradient of wave energy within the breaking zone; and the wave period parameter is determined through spectral analysis to determine the oscillation frequency of the water flow, providing the periodic characteristic input for the bottom shear stress calculation. The initial profile data define the calculation domain boundary: the land boundary is fixed as the backshore or the cliff foot position of the beach, and the underwater closure depth boundary is dynamically calibrated according to the wave breaking critical condition, ensuring that the model domain covers all active sediment transport areas.

[0023] The model core utilizes the bed sediment continuity equation: Equation (1); wherein n p represents the bottom sediment porosity, taking a value of 0.4; z b represents the bottom elevation (m); t represents the geomorphic evolution time; q x represents the total lateral sediment transport rate per unit width (excluding porosity, m 2 / s); and q y represents the total onshore sediment transport rate per unit width (excluding porosity, m 2 / s).

[0024] First, the onshore uniform lateral profile evolution (i.e. ) is calculated, lateral sediment transport simulation is performed only, and the lateral profile change term caused by the onshore sediment transport of the target coast is obtained. In a conventional one-dimensional beach evolution model, the term in the bed sediment continuity equation is often ignored, and onshore uniformity is assumed by default.

[0025] S3, an equivalent onshore distance parameter is introduced to calculate the onshore sediment transport gradient.

[0026] In some embodiments, in S3, the formula of the equivalent onshore distance parameter is: wherein y e represents the equivalent onshore distance parameter, q y represents the onshore sediment transport rate per unit width, and represents the onshore sediment transport gradient.

[0027] In order to effectively calculate the onshore sediment transport gradient, a new parameter, the equivalent onshore distance parameter, is introduced in the present application, which is used to express the range of the onshore sediment transport change that is approximated in the local profile calculation.

[0028] S4, the initial value of the equivalent onshore distance parameter is determined, the onshore sediment transport gradient is input into the one-dimensional beach evolution model, and the onshore elevation change term caused by the onshore sediment transport of the target coast is calculated.

[0029] In some embodiments, the initial value of the equivalent onshore distance parameter is set as the average distance from the wave incidence boundary to the target coastline.

[0030] In the present embodiment, a lateral-onshore bidirectional profile coupling calculation strategy is introduced, the bottom elevation change z b of the target coast caused by the onshore sediment transport is decomposed into a lateral profile change term z x and an onshore elevation change term z y , i.e. ; and the bed sediment continuity equation (i.e. Equation 1) is decomposed into: , equation (2); , equation (3).

[0031] Equation (2) can be solved directly by numerical method; for equation (3), the integral is carried out in a time period with constant water level and wave conditions, and the change of the sediment volume per unit width along the coast is obtained: ; wherein, V y represents the sediment volume per unit width along the coast (i.e., the sediment volume along the coast), ; represents the change of the elevation along the coast caused by the sediment transport along the coast.

[0032] Q y is defined as the time-averaged volume flux per unit width in the coastal direction (m³ / s), ; V y is the sediment volume along the entire cross-section line direction (m³) from t to , also known as the total cross-section sediment volume along the coast, ; then the following relationship can be obtained: ; .

[0033] Assuming that the sediment volume along the coast can be represented by the equivalent coastal distance y e , then ; combined with the formula of , the change of the elevation along the coast in S4 can be solved by the following formula: ; wherein, n p represents the porosity of the bottom sediment; represents the change of the elevation along the coast caused by the sediment transport along the coast; represents the time interval for simulating the evolution of the beach; Q y represents the time-averaged volume flux per unit width in the coastal direction, , x m is the calculation range of the cross-section, and q y is the total sediment transport rate per unit width along the coast.

[0034] This step compresses the two-dimensional sediment gradient effect to a one-dimensional framework by the equivalent coastal distance parameter y e , breaking through the traditional model for ignoring the non-uniformity along the coast.

[0035] S5, superimposing the lateral profile change term and the elevation change term along the coast to obtain the complete target coastal topographic change data caused by the sediment transport along the coast.

[0036] After the calculation of the cross-profile variation term and the alongshore elevation variation term, the step generates the complete terrain variation data by spatial superposition. The cross-profile variation term reflects the vertical erosion and deposition response under the action of wave flow, which is manifested as typical geomorphic forms such as beach shoulder erosion and foreland deposition. The alongshore elevation variation term quantifies the non-uniform transport effect of sediment along the parallel shoreline direction, reflecting the local net erosion or deposition trend.

[0037] S6, iteratively calibrating the equivalent alongshore distance parameter based on the target coastal historical terrain variation data until the terrain variation output by S5 and the target coastal historical terrain variation data have an error less than a preset threshold.

[0038] In some embodiments, the S6 specifically comprises: S61, collecting target coastal historical terrain variation data; The target coastal historical terrain variation data includes shoreline translation position data, measured erosion area and deposition area values, and bottom elevation spatial distribution pattern data of different time periods.

[0039] S62, inputting an initial value of the equivalent alongshore distance parameter into the one-dimensional beach evolution model, executing S1-S5 to obtain complete target coastal terrain variation data caused by alongshore sediment transport; The target coastal terrain variation data caused by alongshore sediment transport includes simulated shoreline recession distance, simulated erosion area and simulated deposition area, and simulated bottom elevation spatial distribution pattern data.

[0040] S63, adjusting the equivalent alongshore distance parameter by an equivalent magnitude (such as ±10% to 20% of the current magnitude), repeating S62 until the terrain variation data and the target coastal historical terrain variation data have an error less than a preset threshold.

[0041] S7, inputting the calibrated equivalent alongshore distance parameter and the real-time collected basic parameters and initial profile of the target coast into the one-dimensional beach evolution model to output terrain variation data caused by alongshore sediment transport.

[0042] In some embodiments, S7 provides an operation process for actual prediction based on the calibrated model. Specifically, the final calibration value obtained by the iterative optimization of S6 is input into the control parameter file of a one-dimensional beach evolution model (such as the CSHORE model) as a fixed parameter. At the same time, real-time collection of current or forecast hydrodynamic and topographic basic data of the target coast is carried out, including basic parameters such as wave incidence angle, wave height, wave period, sediment particle size, settling velocity, specific gravity, and bottom sediment porosity, as well as the latest initial bottom elevation profile data within the range from the land boundary to the closure depth underwater. The above parameters and the initial profile are jointly used as model inputs to drive the model to perform time evolution calculation. Under the combined action of lateral sediment transport and parameterized alongshore sediment transport gradient, the model outputs the topographic change data of the target coast caused by the imbalance of alongshore sediment transport within a future period of time. The output results include but are not limited to the predicted shoreline recession or advance trend, the spatial distribution of profile erosion and deposition, the net sediment loss, and the bottom morphology evolution process. The short-term to medium and long-term evolution trend of the sandy coast is quickly predicted, which is suitable for pre-project evaluation, disaster warning, and shoreline management decision support.

[0043] For example, a certain steep cliff type sandy coast is taken as the application object, which has been long affected by 30° oblique incident waves. Historical monitoring shows that the annual average shoreline recession rate is significant. In order to analyze the influence of non-uniformity of alongshore sediment transport on shoreline evolution, the method of the present application is used to carry out simulation and prediction.

[0044] Data input: wave parameters, incidence angle 30°, wave height average value monitored by buoy, period determined by frequency spectrum analysis; sediment characteristics, median particle size obtained by sieve experiment, settling velocity determined by static water settling column; generated based on unmanned aerial vehicle aerial survey and underwater topographic survey, land boundary is the base of the cliff, and the underwater closure depth is calibrated according to the breaking wave critical depth formula.

[0045] As shown in Figure 2 , the x-axis is the direction perpendicular to the shore (i.e. the lateral sediment transport direction), the y-axis is the alongshore direction (i.e. the alongshore sediment transport direction), and the blue line is the incident wave, , which is the angle between the incident wave and the direction perpendicular to the shore. A lateral profile line is set at y=5m to evaluate the shoreline recession rate in the y=4~6m section. According to the experimental data, it can be analyzed that the alongshore sediment transport rate near y=0 increases rapidly, while in the y=4~6m interval it tends to be stable, and the measured shoreline retreat in this interval is approximately uniform, indicating that the alongshore sediment transport rate changes little, which meets the local uniformity approximation. The initial value of the equivalent alongshore distance parameter is set as the average distance between the wave incidence boundary and the shoreline (7m).

[0046] Historical data are collected, such as the shoreline translation position in the past 5 years (the annual average recession is 3.2m), and the measured values of erosion / deposition area (the erosion proportion is 68%). The initial value y e= 7m, the simulated erosion area is 15% lower than the measured value; adjust y e After 10m, the simulated erosion area accounts for 70%, the error of shoreline recession distance is less than 5%, and the spatial distribution of bed elevation is 92%, which meets the convergence condition.

[0047] As shown in the figure, the blue curve represents the calculated initial beach profile; the red curve is the calculated bed elevation Figure 3 evolution result, where the gradient term of alongshore sediment transport is ignored . The result corresponds to the traditional one-dimensional beach evolution model, which only considers the transverse sediment transport effect, so it shows the "local conservation" feature that the erosion area and the accumulation area are equal. The black curve represents the calculation of the gradient term of alongshore sediment transport into the model, which reflects the comprehensive effect of considering transverse sediment transport and alongshore sediment transport gradient. In this calculation, the equivalent alongshore distance parameter y e = 10m is obtained by model test calibration. The simulation result shows that the total erosion area of the profile is significantly larger than the accumulation area, indicating that the transverse profile is affected by the unevenness of alongshore sediment transport, and a net erosion process occurs, so the shoreline appears a overall recession trend.

[0048] In the embodiment of the steep cliff coast, the calibration and application of the equivalent alongshore distance parameter significantly improve the physical accuracy and engineering practicability of beach evolution prediction. When a 30° oblique incident wave acts on the steep cliff coast, the traditional one-dimensional model always presents a false balance state with equal erosion area and accumulation area due to the ignorance of the alongshore sediment transport gradient Figure 3 (red curve), which cannot explain the continuous recession of the measured shoreline. By optimizing the equivalent alongshore distance parameter to a reasonable range Figure 3 (black curve) through the dynamic calibration mechanism, the model accurately quantifies the non-uniformity of alongshore sediment transport while retaining the one-dimensional calculation efficiency. The model successfully reproduces the net loss feature that the erosion area is significantly larger than the accumulation area, and the error of shoreline recession distance is reduced to a very low level.

[0049] The present application also provides a sandy coast alongshore sediment transport calculation system for the above-mentioned sandy coast alongshore sediment transport calculation method, comprising: a data input module for obtaining the basic parameters and initial profile of the target coast; a transverse profile simulation module for inputting the basic parameters and initial profile into a one-dimensional beach evolution model to obtain the transverse profile change term of the target coast caused by alongshore sediment transport; a alongshore sediment transport gradient calculation module for introducing an equivalent alongshore distance parameter to calculate the alongshore sediment transport gradient; ​a coastal elevation simulation module, configured to determine an initial value of an equivalent coastal distance parameter, input the coastal sediment transport gradient into a one-dimensional beach evolution model, and calculate a coastal elevation change item caused by the coastal sediment transport of the target coast; a terrain change acquisition module, configured to superimpose the lateral profile change item and the coastal elevation change item to obtain complete terrain change data of the target coast caused by the coastal sediment transport; a calibration module, configured to iteratively calibrate the equivalent coastal distance parameter based on historical bottom elevation change data of the target coast until the terrain change output by the terrain change acquisition module has an error less than a preset threshold value from the historical terrain change data of the target coast; a result output module, configured to input the calibrated equivalent coastal distance parameter and real-time collected basic parameters and initial profile of the target coast into the one-dimensional beach evolution model, and output terrain change data caused by the coastal sediment transport.

[0050] It should be noted that the terms used in the present application are only for describing specific embodiments, and are not intended to limit the scope of the present application. As shown in the specification of the present application, unless the context clearly indicates otherwise, the words "one", "a", "an", and / or "the" do not specifically refer to the singular, but also include the plural. The terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method or device including the element.

[0051] It should also be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. Unless otherwise specified and limited, the terms "mount", "connect", "connect" and the like should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0052] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present application.

Claims

1. A method of calculating the alongshore transport of sediment at a sandy coast, characterized by, The method comprises the following steps: S1, obtaining basic parameters and an initial profile of a target coast; S2, inputting the basic parameters and the initial profile into a one-dimensional beach evolution model to obtain a horizontal profile variation term of the target coast caused by alongshore sediment transport; The one-dimensional beach evolution model is a CSHORE model; S3, introducing an equivalent alongshore distance parameter to calculate an alongshore sediment transport gradient; S4, determining an initial value of the equivalent alongshore distance parameter, inputting the alongshore sediment transport gradient into the one-dimensional beach evolution model to calculate an alongshore elevation variation term of the target coast caused by alongshore sediment transport; S5, superimposing the horizontal profile variation term and the alongshore elevation variation term to obtain complete topographic variation data of the target coast caused by alongshore sediment transport; S6, iteratively calibrating the equivalent alongshore distance parameter based on historical topographic variation data of the target coast until the topographic variation data output in S5 has an error less than a preset threshold value from the historical topographic variation data of the target coast; S7, inputting the calibrated equivalent alongshore distance parameter and real-time collected basic parameters and an initial profile of the target coast into the one-dimensional beach evolution model to output topographic variation data caused by alongshore sediment transport.

2. The method of claim 1, wherein, In S1, the basic parameters include a wave incidence angle, a wave height, a wave period, a sediment particle size, a sedimentation velocity, a specific gravity, and a bottom sediment porosity; and the initial profile includes land boundary and bottom elevation data within a closed underwater depth range, and the closed underwater depth is determined by a wave breaking critical condition.

3. The method of claim 1, wherein, The formula of the equivalent alongshore distance parameter in S3 is: where y e represents the equivalent alongshore distance parameter, q y represents the unit width alongshore sediment transport rate, represents the alongshore sediment transport gradient.

4. The method of claim 1, wherein, The initial value of the equivalent alongshore distance parameter is set as an average distance from a wave incidence boundary to a coastline of the target coast.

5. The method of claim 1, wherein, In S4, the alongshore elevation variation term is solved by the following formula: ； where n p represents the porosity of the bottom sediment; represents the amount of change in the coastal elevation due to the coastal sediment transport; represents the time interval for simulating the evolution of the beach; Q y represents the time-averaged volume flux per unit width in the coastal direction, , x m is the calculation range of the cross section, q y is the total sediment transport rate per unit width in the coastal direction.

6. The method of claim 1, wherein, S6 specifically comprises: S61, collecting historical topographic variation data of the target coast; S62, inputting the initial value of the equivalent alongshore distance parameter into the one-dimensional beach evolution model to execute S1-S5 to obtain complete topographic variation data of the coastline of the target coast caused by alongshore sediment transport; S63, adjusting the equivalent alongshore distance parameter by an equal order of magnitude, and repeating S62 until the topographic variation data has an error less than a preset threshold value from the historical topographic variation data of the target coast.

7. A method of calculating the sediment transport along a sandy coast according to claim 6, characterized in that, In S61, the historical topographic variation data of the target coast includes coastline translation position data, measured values of erosion area and deposition area, and bottom elevation spatial distribution form data at different time periods; In S62, the topographic variation data of the target coast caused by alongshore sediment transport includes simulated coastline recession distance, simulated erosion area and deposition area, and simulated bottom elevation spatial distribution form data.

8. A system for calculating the alongshore sediment transport of a sandy coast, for performing the method for calculating the alongshore sediment transport of a sandy coast according to any one of claims 1 to 7, characterized in that, The method comprises: a data input module for obtaining basic parameters and an initial profile of a target coast; a horizontal profile simulation module for inputting the basic parameters and the initial profile into a one-dimensional beach evolution model to obtain a horizontal profile variation term of the target coast caused by alongshore sediment transport; an alongshore sediment transport gradient calculation module for introducing an equivalent alongshore distance parameter to calculate an alongshore sediment transport gradient; an alongshore elevation simulation module for determining an initial value of the equivalent alongshore distance parameter, inputting the alongshore sediment transport gradient into the one-dimensional beach evolution model to calculate an alongshore elevation variation term of the target coast caused by alongshore sediment transport; and The terrain change obtaining module is configured to superimpose the lateral profile change term and the alongshore elevation change term to obtain complete terrain change data of the target coast caused by alongshore sediment transport; The calibration module is configured to iteratively calibrate the equivalent alongshore distance parameter based on historical terrain change data of the target coast until the terrain change output by the terrain change obtaining module has an error less than a preset threshold value with the historical terrain change data of the target coast; The result output module is configured to input the calibrated equivalent alongshore distance parameter and the basic parameters and the initial profile of the target coast collected in real time into a one-dimensional beach evolution model to output terrain change data caused by alongshore sediment transport.

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