Method and device for calculating hydrological connectivity between river-lake floodplain and main channel, electronic equipment and medium

Abstract

This disclosure relates to the field of water conservancy engineering technology, specifically to a method, device, electronic equipment, and medium for calculating the hydrological connectivity between river and lake floodplains and main channels. The method includes: acquiring characteristic cross-sectional topographic data of the water area to be analyzed; calculating the floodplain-channel boundary using a hydraulic depth objective function; constructing a function relating the water-passing area, wetted perimeter, and water level of the main channel and floodplain to obtain the water conveyance capacity function of the main channel and floodplain; obtaining the average flow velocity function of the main channel by combining the total flow process; identifying the start and end times of floodplain hydrological connectivity events based on water level, flow process, and floodplain-channel boundary; calculating the floodplain's water storage and drainage exchange volume and entrainment exchange volume respectively, and finally determining the floodplain-channel hydrological connectivity of the floodplain hydrological connectivity events. Based on cross-sectional topographic and hydrological process data, this disclosure can obtain hydrological connectivity indicators without complex two-dimensional / three-dimensional simulations, providing a reliable technical basis for floodplain-channel management, ecological restoration, and engineering scheduling.

Description

Technical Field

[0001] This disclosure relates to the field of water conservancy engineering technology, specifically to a method, device, electronic equipment, and medium for calculating the hydrological connectivity between river and lake floodplains and main channels. Background Technology

[0002] River and lake floodplains serve as transitional zones between the terrestrial systems of rivers and lakes and the aquatic systems of rivers and lakes. They are areas with the highest productivity, most active biological processes, and greatest biodiversity within these systems. Floodplain-channel connectivity provides pathways and power sources for the exchange of biogenic and biological matter between aquatic and terrestrial systems, playing a crucial role in maintaining the ecological integrity of rivers and lakes and being key to preserving their biodiversity and ecological functions. However, the disorderly use and overexploitation of floodplain resources have led to the widespread solidification, hardening, and fragmentation of river and lake shorelines. Furthermore, the construction and operation of water conservancy projects have altered the natural water and sediment processes of rivers and lakes, resulting in increasingly significant obstruction of floodplain-channel ecological connectivity. This has damaged the ecological integrity of rivers and lakes and limited their comprehensive functions.

[0003] From a hydrodynamic perspective, during flood events, the water passage space of rivers and lakes is jointly formed by the main channel and the floodplain, and a significant water exchange process occurs between the main channel and the floodplain. This exchange process is controlled by water level fluctuations, manifested as the floodplain filling with water during the rising period and draining water during the falling period, forming a reciprocating storage and discharge exchange at the event scale. On the other hand, when the floodplain continues to overflow and there is a significant velocity difference between the main channel and the floodplain, a transverse shear layer and its associated secondary flow and vortex structures form at the boundary between the channel and the floodplain, causing water from the main channel to be continuously drawn into the floodplain and transported back, forming a continuous mixing exchange. These two types of processes together determine the scale, duration, and intensity of water exchange between the channel and the floodplain, and are important hydrodynamic foundations influencing sediment transport and geomorphological evolution in floodplains, the exchange of nutrients and dissolved substances, and the response of floodplain vegetation and aquatic habitats to hydrological changes.

[0004] In current engineering applications, the quantitative evaluation of channel-shoal hydrological connectivity still has significant shortcomings. On the one hand, commonly used one-dimensional zonal hydraulic calculations typically focus on solving for flow capacity and distribution flow under given water level or flow conditions, making it difficult to directly characterize the bidirectional exchange volume, exchange rate, and their variations with process stages between channels and shoals at the event scale. Consequently, it is difficult to form connectivity indicators that can be used for comparison between river segments and events. On the other hand, although two-dimensional or three-dimensional numerical simulations can calculate velocity fluxes and obtain exchange volumes at interfaces, they are highly dependent on high-precision topography, boundary conditions, and parameter calibration, have long modeling cycles, and high computational costs, making it difficult to meet the operational analysis needs of multiple river segments, multiple events, and long-term series.

[0005] Therefore, there is an urgent need for a computational method that allows for easy access to input data, reproducible calculation processes, simultaneous characterization of floodplain distribution and floodplain water exchange intensity, and the formation of comparable connectivity indices at the event scale. This method would support quantitative research on the evolution of river and lake floodplains and the response of habitat processes to hydrological changes, and provide reliable technical support for floodplain management, ecological restoration, and engineering scheduling. Summary of the Invention

[0006] To address the problems in the related technologies, this disclosure provides a method, apparatus, electronic device, and medium for calculating the hydrological connectivity between river and lake floodplains and main channels.

[0007] In a first aspect, this disclosure provides a method for calculating the hydrological connectivity between river and lake floodplains and the main channel, including:

[0008] Obtain characteristic cross-sectional topographic data of the water area to be analyzed; Based on the characteristic cross-sectional topographic data, the boundary of the shoal and channel in the area to be analyzed is calculated using the hydraulic depth objective function method; Based on the characteristic cross-sectional topographic data and the floodplain boundary, construct the following functions: the relationship between the main channel's water-passing area and water level, the relationship between the floodplain's water-passing area and water level, the relationship between the main channel's wetted perimeter and water level, and the relationship between the floodplain's wetted perimeter and water level. The main channel water conveyance capacity function is obtained based on the relationship function between the main channel water flow area and water level and the relationship function between the main channel wetted perimeter and water level; the floodplain water conveyance capacity function is obtained based on the relationship function between the floodplain water flow area and water level and the floodplain wetted perimeter and water level. The average velocity function of the main channel is obtained based on the water conveyance capacity function of the main channel, the water conveyance capacity function of the floodplain, and the flow rate function of the area to be analyzed. Based on the water level function and flow function of the water area to be analyzed and the boundary of the floodplain, the start and end time periods of the floodplain hydrological connectivity event are determined. Based on the start and end times of the floodplain hydrological connectivity event and the relationship function between the floodplain water flow area and the water level, calculate the floodplain surface water storage and drainage exchange volume driven by water level fluctuations during the floodplain hydrological connectivity event. Based on the start and end times of the floodplain hydrological connectivity event and the average flow velocity function of the main channel, calculate the entrainment exchange volume dominated by secondary flow in the floodplain hydrological connectivity event. The floodplain hydrological connectivity of the floodplain hydrological connectivity event is calculated based on the start and end times of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

[0009] According to an embodiment of this disclosure, the characteristic cross-section topographic data includes multiple sets of characteristic cross-section topographic data corresponding to multiple characteristic cross-sections. Each set of characteristic cross-section topographic data includes multiple sets of measuring point data for the corresponding characteristic cross-section. Each set of measuring point data includes the distance between measuring points distributed along the horizontal direction of the cross-section and the elevation value corresponding to the distance between the measuring points. The step of calculating the floodplain / channel delineation boundary of the area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data includes: For any given characteristic cross section, based on the corresponding topographic data of the characteristic cross section, the water level boundary between the floodplain and the main channel of the given characteristic cross section is calculated using the hydraulic depth objective function method. The boundary between the floodplain and the main channel of the water level is determined based on the water level boundary point of each characteristic cross section.

[0010] According to embodiments of this disclosure, the step of calculating the water level boundary between the floodplain and the main channel of any characteristic cross-section using the hydraulic depth objective function method based on the corresponding characteristic cross-section topographic data includes: Based on the corresponding characteristic cross-section topographic data, calculate the water-passing area and water-passing width of any characteristic cross-section at the preset water level; Based on the water passage area and the water passage width, calculate the hydraulic depth of any characteristic cross section at the preset water level; Based on the water passage width and the preset water level change step size, the central difference method is used to calculate the growth rate of the water passage width with respect to the water level. Based on the growth rate of the water level with respect to the water passage width and the hydraulic depth, a hydraulic depth objective function is constructed; The elevation value of the measuring point at the lower edge of the floodplain of any characteristic cross section is determined based on the water level corresponding to the maximum value of the hydraulic depth objective function, and the elevation value of the measuring point at the lower edge of the floodplain is used as the water level boundary between the floodplain and the main channel of any characteristic cross section.

[0011] According to embodiments of this disclosure, obtaining the main channel water conveyance capacity function based on the relationship function between the main channel's water flow area and water level, and the relationship function between the main channel's wetted perimeter and water level, includes: The main channel water conveyance capacity function is obtained using the following formula. : ; ; The step of obtaining the floodplain water conveyance capacity function based on the relationship function between the floodplain water-passing area and the water level and the relationship function between the floodplain wetted perimeter and the water level includes: The floodplain water conveyance capacity function is obtained using the following formula. : ; ; The step of obtaining the average velocity function of the main channel based on the main channel water conveyance capacity function, the floodplain water conveyance capacity function, and the flow rate function of the area to be analyzed includes: The average flow velocity function of the main channel is obtained by the following formula. : ; ; in, Indicates the Manning roughness of the main groove. Indicates the roughness of the floodplain Manning. This represents a function relating the water flow area of ​​the main channel to the water level. This represents the function relating the wetted perimeter of the main tank to the water level. This represents a function relating the floodplain's surface area to the water level. This represents the function relating the wetted perimeter of the floodplain to the water level. This represents the flow function of the water area to be analyzed.

[0012] According to embodiments of this disclosure, calculating the floodplain water storage and drainage exchange volume driven by water level fluctuations during the floodplain hydrological connectivity event, based on the start and end times of the floodplain hydrological connectivity event and the relationship function between the floodplain water area and water level, includes: The time variation function of the floodplain's water-passing area is obtained by differentiating the function of the relationship between the floodplain's water-passing area and the water level with respect to time. Based on the time variation function of the floodplain water surface, the effective length of the water area to be analyzed, and the start and end time of the floodplain hydrological connectivity event, calculate the floodplain surface water storage and drainage exchange volume driven by water level fluctuations in the floodplain hydrological connectivity event. The step of calculating the entrainment exchange volume dominated by secondary currents in the floodplain hydrological connectivity event based on the start and end times of the event and the average velocity function of the main channel includes: Construct a volume exchange flux function per unit interface length based on the average flow velocity function of the main channel, the characteristic water depth at the boundary of the shoal and channel division, and the preset entrainment coefficient. Construct an instantaneous exchange flow function based on the unit interface length volume exchange flux function and the length of the beach-channel boundary; The entrainment exchange volume dominated by secondary flow in the floodplain hydrological connectivity event is calculated based on the instantaneous exchange flow function and the start and end time periods of the floodplain hydrological connectivity event.

[0013] According to embodiments of this disclosure, the step of calculating the floodplain hydrological connectivity of the floodplain hydrological connectivity event based on the start and end times of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed includes: The sum of the surface water storage and drainage exchange volume and the entrainment exchange volume is taken as the cumulative exchange volume of the floodplain hydrological connectivity event. The total water volume of the floodplain hydrological connectivity event is calculated based on the start and end times of the event and the flow function of the water area to be analyzed. The floodplain hydrological connectivity of the floodplain hydrological connectivity event is calculated based on the cumulative exchange volume and the total water flow volume of the water area.

[0014] According to embodiments of this disclosure, the method further includes: Obtain multi-scale floodplain hydrological connectivity corresponding to one or more floodplain hydrological connectivity events occurring during the proposed analysis period; the multi-scale floodplain hydrological connectivity includes one or more of the following: annual scale floodplain hydrological connectivity, monthly scale floodplain hydrological connectivity, and daily scale floodplain hydrological connectivity. Based on the multi-scale floodplain hydrological connectivity and / or the floodplain hydrological connectivity of each floodplain hydrological connectivity event occurring during the proposed analysis period, a sequence of floodplain hydrological connectivity change characteristics is statistically generated during the proposed analysis period.

[0015] Secondly, this disclosure provides a device for calculating the hydrological connectivity between floodplains and main channels, comprising: The beach-channel boundary delineation module is configured to: acquire characteristic cross-sectional topographic data of the water area to be analyzed; and calculate the beach-channel delineation boundary of the water area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data. The floodplain hydrological parameter calculation module is configured to: construct, based on the characteristic cross-sectional topographic data and the floodplain boundary, a function relating the main channel's water-passing area to water level, a function relating the floodplain's water-passing area to water level, a function relating the main channel's wetted perimeter to water level, and a function relating the floodplain's wetted perimeter to water level; obtain the main channel's water conveyance capacity function based on the main channel's water-passing area to water level and the main channel's wetted perimeter to water level; obtain the floodplain's water conveyance capacity function based on the floodplain's water-passing area to water level and the floodplain's wetted perimeter to water level; and obtain the floodplain's water conveyance capacity function based on the main channel's water conveyance capacity function and the floodplain's water-passing area to water level. The average velocity function of the main channel is obtained from the water capacity function and the flow function of the water area to be analyzed; the start and end time periods of the floodplain hydrological connectivity event are determined based on the water level function and flow function of the water area to be analyzed and the boundary of the floodplain and the channel; the volume of water storage and drainage exchange driven by water level fluctuations in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the relationship function between the floodplain water area and water level; the volume of entrainment exchange dominated by secondary flow in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the average velocity function of the main channel. The floodplain hydrological connectivity calculation module is configured to calculate the floodplain hydrological connectivity of the floodplain hydrological connectivity event based on the start and end time period of the floodplain hydrological connectivity event, the floodplain water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

[0016] Thirdly, this disclosure provides an electronic device including a memory and a processor; the memory is used to store computer instructions, wherein the computer instructions are executed by the processor to implement the method described in the first aspect.

[0017] Fourthly, this disclosure provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the method described in the first aspect.

[0018] According to the technical solution provided in this disclosure, firstly, characteristic cross-sectional topographic data of the water area to be analyzed is obtained; based on the characteristic cross-sectional topographic data, the floodplain boundary of the water area to be analyzed is calculated using the hydraulic depth objective function method; then, based on the characteristic cross-sectional topographic data and the floodplain boundary, the following functions are constructed: main channel flow area versus water level, floodplain flow area versus water level, main channel wetted perimeter versus water level, and floodplain wetted perimeter versus water level; the main channel water conveyance capacity function is obtained based on the main channel flow area versus water level function and the main channel wetted perimeter versus water level function; the floodplain water conveyance capacity function is obtained based on the floodplain flow area versus water level function and the floodplain wetted perimeter versus water level function; the main channel water conveyance capacity function is obtained based on the main channel water conveyance capacity function and the floodplain water conveyance capacity function. The average velocity function of the main channel is obtained from the flow function of the water area to be analyzed; the start and end time periods of the floodplain hydrological connectivity event are determined based on the water level function and flow function of the water area to be analyzed, as well as the boundary of the floodplain and channel; the volume of water storage and drainage exchange driven by water level fluctuations in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the relationship function between the floodplain water area and water level; the volume of entrainment exchange dominated by secondary flow in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the average velocity function of the main channel; finally, the floodplain hydrological connectivity degree of the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event, the volume of water storage and drainage exchange on the floodplain, the volume of entrainment exchange, and the flow function of the water area to be analyzed.

[0019] The technical solution disclosed herein transforms the complex hydrological connectivity problem of river and lake floodplains into an analytical computational problem based on cross-sectional topography and hydrological processes by constructing a computational framework of "hydraulic-driven decomposition - process separation and accounting - volume normalization". This framework enables floodplain-channel diversion calculations to be completed even when conditions are unavailable or inconvenient for developing three-dimensional numerical models, utilizing readily available cross-sectional topography, water level, and flow data. It quantifies the floodplain storage and drainage exchange volume driven by water level fluctuations and the entrainment exchange volume dominated by secondary flows, thereby constructing a dimensionless hydrological connectivity index that can be analyzed over long-term series and compared laterally. This solves the problems in existing technologies, such as the difficulty in stably obtaining the main channel and floodplain flow distribution results under known total flow conditions, the difficulty in further quantifying the scale and intensity of water exchange between floodplains and channels, and the difficulty in forming a hydrological connectivity index at the event scale that can be used for comparison between different river sections and different flood processes. This supports quantitative research on the evolution of river and lake floodplains and the response of habitat processes to hydrological changes, and provides a reliable technical basis for floodplain management, ecological restoration, and engineering scheduling.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0021] Other features, objects, and advantages of this disclosure will become more apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings. In the drawings: Figure 1 A flowchart illustrating a method for calculating the hydrological connectivity between a river floodplain and the main channel according to an embodiment of the present disclosure is shown. Figure 2 A flowchart illustrating a method for calculating the water level boundary between the floodplain and the main channel in a characteristic cross section according to an embodiment of the present disclosure; Figure 3 A graph showing the relationship between the hydraulic depth objective function and water level according to an embodiment of the present disclosure is provided. Figure 4 A schematic diagram showing a characteristic cross-section according to an embodiment of the present disclosure; Figure 5 A flowchart illustrating another method for calculating the hydrological connectivity between a river floodplain and the main channel according to an embodiment of this disclosure is shown. Figure 6 A calculated curve of the daily floodplain-channel hydrological connectivity of the Wuguizhou River section in 2016 is shown according to an embodiment of the present disclosure. Figure 7 A structural block diagram of a device for calculating the hydrological connectivity of a river floodplain and main channel according to an embodiment of the present disclosure is shown. Figure 8 A structural block diagram of another device for calculating the hydrological connectivity of a river floodplain and main channel according to an embodiment of the present disclosure is shown. Figure 9 A structural block diagram of an electronic device according to an embodiment of the present disclosure is shown. Detailed Implementation

[0022] In the following, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement them. Furthermore, for clarity, portions unrelated to the description of exemplary embodiments have been omitted from the drawings.

[0023] In this disclosure, it should be understood that terms such as “comprising” or “having” are intended to indicate the presence of features, figures, steps, behaviors, components, parts or combinations thereof disclosed in this specification, and are not intended to exclude the possibility of the presence or addition of one or more other features, figures, steps, behaviors, components, parts or combinations thereof.

[0024] It should also be noted that, unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other. This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] In this disclosure, any operation involving the acquisition of user information or user data, or the display of user information or user data to others, is an operation authorized or confirmed by the user, or actively selected by the user.

[0026] As mentioned earlier, existing technologies have significant shortcomings in quantitatively evaluating the hydrological connectivity between floodplains and main channels. While traditional zonal hydraulic calculations can solve for flow capacity, they struggle to characterize the bidirectional exchange volume between floodplains and channels at event scales and its dynamic characteristics as water levels fluctuate. Although two-dimensional or three-dimensional numerical simulations can accurately calculate exchange fluxes, they are overly dependent on high-precision topographic data and boundary conditions, have long modeling cycles, and high computational costs, making it difficult to meet the operational analysis needs of multiple river segments, multiple events, and long-term time series.

[0027] How to overcome the problems existing in the prior art? This disclosure, through in-depth analysis of the physical mechanisms of floodplain hydrological connectivity, discovers that the exchange of water between the floodplain and the channel is actually driven by two different processes: one is the floodplain's storage and drainage process that occurs with the rise and fall of water levels, and the other is the secondary flow entrainment and mixing process caused by the velocity difference at the floodplain-channel boundary. Based on this discovery, this disclosure proposes a method for calculating the hydrological connectivity between river and lake floodplains and the main channel. The core idea is to decompose the complex floodplain connectivity problem into the two physical mechanisms mentioned above and perform process accounting separately, then construct a dimensionless connectivity index through volume normalization. Specifically, firstly, the floodplain-channel boundary is automatically identified based on cross-sectional topographic data, establishing the hydraulic geometry relationship between the main channel and the floodplain; then, combining water level and flow processes, the volume of floodplain storage and drainage exchange driven by water level fluctuations and the volume of entrainment exchange dominated by secondary flows are calculated separately; finally, the hydrological connectivity is defined as the ratio of the cumulative exchange volume of events to the total flow volume, thereby achieving a unified measurement and horizontal comparison of the connectivity intensity between different river sections and different events. Through this technical concept, this disclosure aims to solve the problems in the prior art of making it difficult to quantify the exchange of water bodies in the floodplain at the event scale and to form comparable connectivity indicators, so as to provide a quantitative tool for the ecological assessment and engineering management of river and lake floodplains that is easy to obtain data, reproducible in calculation, and comparable in results.

[0028] Figure 1 A flowchart illustrating a method for calculating the hydrological connectivity between a river / lake floodplain and the main channel according to an embodiment of this disclosure is shown. Figure 1 As shown, the method includes the following steps S110~S170: In step S110, characteristic cross-sectional topographic data of the water area to be analyzed are obtained.

[0029] The term "water area" in this disclosure refers to water bodies such as rivers, lakes, reservoirs, ponds, and coastal zones, as well as other water bodies with floodplain-deep channel structures; "the water area to be analyzed" refers to the target river section, lake shore area, etc., that requires hydrological connectivity assessment.

[0030] The "characteristic cross-section" disclosed herein refers to a transverse profile of a river channel or lake shore that can represent the typical topographic features of a specific section of a water body. This profile is perpendicular to the main channel direction or shoreline orientation and is used to depict the geometry of the main channel and floodplain within that section, including key topographic features such as main channel depth, floodplain width, and slope gradient. Generally, a cross-section can be taken every 100 to 500 meters. In water bodies with gentle longitudinal topographic changes, the cross-section interval can be appropriately increased; in water bodies with dramatic topographic changes, the cross-section layout needs to be more dense to ensure that the selected characteristic cross-sections can effectively represent the topographic features of that section.

[0031] The "characteristic cross-sectional topographic data" involved in this disclosure refers to a set of discretized spatial coordinate data constituting a characteristic cross-section. In this disclosure, the characteristic cross-sectional topographic data includes multiple sets of characteristic cross-sectional topographic data corresponding to multiple characteristic cross-sections. Each set of characteristic cross-sectional topographic data includes multiple sets of measuring point data for the corresponding characteristic cross-section. Each set of measuring point data includes the distance between measuring points distributed along the horizontal direction of the cross-section and the elevation value corresponding to the measuring point distance, i.e., in the form of... The data set. Among them, Indicates the number of measuring points and the distance between measuring points. Indicates the first The horizontal distance and elevation value of each measuring point relative to the starting point of the cross-section (usually a fixed reference point on the left bank). Indicates the first The vertical height of a measuring point relative to a certain reference surface (such as the Yellow Sea Height System) is recorded. The data from this measuring point fully describes the underwater and terrestrial topography at the cross-section, and forms the basis for subsequent beach-channel delineation and the construction of hydraulic geometry.

[0032] When acquiring the characteristic cross-sectional topographic data of the water area to be analyzed, one or more characteristic cross-sections are first laid out according to the topographic change characteristics of the water area to be analyzed. Then, the characteristic cross-sectional topographic data is acquired through field measurements, digital elevation model (DEM) data extraction or historical data collection.

[0033] In step S120, the beach-channel delineation boundary of the proposed analysis water area is calculated using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data.

[0034] The "floodplain" and "main channel" mentioned in this disclosure refer to the "floodplain" and "main channel". The "floodplain" refers to the beach area located on both sides of the main channel, which is submerged by water during the flood season or high water season and exposed by water during the dry season or normal water season. This area is an important part of the water-land transition zone and has the hydrological characteristics of periodic submersion and exposure. The "main channel", also known as the deep channel or main river channel, refers to the channel-shaped area through which water mainly flows during the dry season or normal water season. It is usually located at the lowest point of the cross-sectional topography and is the core channel for concentrated flow. In the river scenario, the "floodplain" refers to the river floodplain and the "main channel" refers to the main channel of the riverbed. In the lake scenario, the "floodplain" refers to the lake shore beach or drawdown zone and the "main channel" refers to the deep water area of ​​the lake. Together, they constitute a dual structure of floodplain and main channel with hydrological connectivity.

[0035] To delineate the floodplain and main channel, this disclosure specifically uses characteristic cross-sectional topographic data and a hydraulic depth objective function method to automatically and objectively identify the spatial boundary line between the main channel and the floodplain (i.e., the lower edge of the floodplain), providing a unified geometric basis for subsequent zonal hydraulic calculations and water exchange accounting. This step solves the problems of strong subjectivity, difficulty in reproduction, and inconsistent delineation standards between different cross-sections caused by relying on manual experience to delineate floodplain and channel boundaries in traditional methods, ensuring the repeatability and consistency of floodplain and channel delineation results.

[0036] According to embodiments of this disclosure, the step of calculating the floodplain / channel delineation boundary of the area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data includes: First, for any characteristic cross section, based on the corresponding characteristic cross section topographic data, the water level boundary between the floodplain and the main channel of the characteristic cross section is calculated using the hydraulic depth objective function method.

[0037] Figure 2 A flowchart illustrating a method for calculating the water level boundary between the floodplain and the main channel in a characteristic cross-section according to an embodiment of the present disclosure is shown. Figure 2 As shown, for any characteristic cross-section, calculate the water level boundary between the floodplain and the main channel according to the following steps S121~S125: In step S121, based on the corresponding characteristic cross-section topographic data, the water-passing area and water-passing width of any characteristic cross-section at the preset water level are calculated.

[0038] For example, for any characteristic cross-section, its characteristic cross-sectional topographic data is represented as: ; Within the preset water level calculation range Within, based on the preset water level change step size Generate a series of candidate water levels ,in .

[0039] For any candidate water level Interpolation is performed on characteristic cross-sectional topographic data to determine water levels. The water flow area for all the following water flow regions is obtained by integrating the area of ​​each infinitesimal element within the water flow region using the following formula. : ; in, and Indicates water level The corresponding left and right water crossing boundaries.

[0040] Water passage width The horizontal distance between the left and right water boundaries can be directly taken as follows: ; In step S122, the hydraulic depth of any characteristic cross section at the preset water level is calculated based on the water flow area and the water flow width.

[0041] Hydraulic depth reflects the average depth of water flow at the preset water level and is an important parameter characterizing flow efficiency. Water level The depth of the water conservancy It can be represented as: ; In step S123, the rate of increase of the water level with respect to the water width is calculated using the central difference method based on the water width and the preset water level change step size.

[0042] The growth rate of the water passage width with respect to water level characterizes the intensity of the abrupt change in the cross-sectional geometry as the water level rises. The growth rate of the water passage width with respect to water level is calculated using the following formula. : ; Among them, the central difference method has higher computational accuracy compared to the forward or backward difference method.

[0043] In step S124, a hydraulic depth objective function is constructed based on the growth rate of the water level with respect to the water width and the hydraulic depth.

[0044] Specifically, the objective function for hydraulic depth is constructed by multiplying the growth rate of the water passage width by the hydraulic depth. It can be expressed by the following formula: ; This function comprehensively reflects two key characteristics: the intensity of the abrupt change in the width of the floodplain and the average depth of the flow. The product of these two characteristics peaks at the initiation point of the floodplain.

[0045] In step S125, the elevation value of the measuring point where the lower edge of the floodplain of any characteristic cross section is located is determined according to the water level corresponding to the maximum value of the hydraulic depth objective function, and the elevation value of the measuring point where the lower edge of the floodplain is located is used as the water level boundary point between the floodplain and the main channel of any characteristic cross section.

[0046] Specifically, iterate through all candidate water levels. To find the water level that maximizes the objective function of hydraulic depth. The water level The water level at the lower edge of the floodplain of this characteristic cross-section is determined. The elevation value of the measuring point where the lower edge of the floodplain water level intersects with the floodplain is the water level boundary between the floodplain and the main channel of this cross-section. Wherein: ; Figure 3 The diagram illustrates the relationship between the hydraulic depth objective function and water level according to embodiments of the present disclosure, specifically showing the original J-value curve and the smoothed J-value curve to identify the maximum point of the hydraulic depth objective function. Figure 3 It can be seen that the hydraulic depth objective function exhibits multiple peaks as the water level changes. Among them, peak 3 is the maximum value of the hydraulic depth objective function, and the corresponding water level is... This refers to the water level at the lower edge of the floodplain of this characteristic cross-section.

[0047] When the water level is lower At that time, the water flow is mainly confined within the main channel; when the water level rises to... At this point, the water begins to overflow into the beach, the cross-sectional width increases significantly, and water exchange between the beach and the channel begins to occur.

[0048] Figure 4 A schematic diagram of a characteristic cross-section according to an embodiment of the present disclosure is shown. Specifically, this embodiment uses the Wuguizhou River section as an example, employing a typical cross-section in the middle as the characteristic cross-section, such as... Figure 4 As shown, the point where the water level at the lower edge of the floodplain meets the floodplain itself is the lower edge point, which is the water level boundary between the floodplain and the main channel at this cross-section. The water level at the upper edge of the floodplain... Generally, it is the highest annual flood level. The point where the water level at the upper edge of the floodplain meets the floodplain is the upper edge point of the floodplain. The area below the water level at the lower edge is the main channel, and the area between the water level at the lower edge and the upper edge is the floodplain.

[0049] Then, for multiple characteristic cross sections laid out in the water area to be analyzed, repeat the above steps S121~S125 to obtain the water level boundary point of each characteristic cross section.

[0050] Finally, the floodplain and main channel boundary is determined based on the water level boundary points between the floodplain and the main channel at each characteristic cross-section. For example, the continuously varying floodplain and channel boundary can be obtained by linearly interpolating the water level boundary points along the flow path using interpolation.

[0051] In step S130, based on the characteristic cross-sectional topographic data and the floodplain boundary, the following functions are constructed: the relationship between the main channel's water-passing area and water level, the relationship between the floodplain's water-passing area and water level, the relationship between the main channel's wetted perimeter and water level, and the relationship between the floodplain's wetted perimeter and water level.

[0052] The core objective of step S130 is to construct hydraulic geometric relationship functions for the main channel region and the floodplain region based on characteristic cross-sectional topographic data and the determined floodplain boundaries. This provides a quantitative functional basis for subsequent water conveyance capacity calculation, flow allocation, and water exchange accounting. This step transforms discrete cross-sectional topographic data into continuous hydraulic geometric relationships, enabling the rapid acquisition of the flow area and wetted perimeter of the main channel and floodplain at any water level, thereby realizing the conversion from "discrete topographic points" to "continuous hydraulic functions".

[0053] Among them, the relationship between the water flow area and the water level is used to describe the size of the cross-sectional area of ​​the water flow in the corresponding area at different water levels, reflecting the flow capacity of the area; the relationship between the wetted perimeter and the water level is used to describe the perimeter length of the water body in contact with the solid boundary at different water levels, reflecting the resistance characteristics of the boundary.

[0054] In practical implementation, the cross-section is first divided into the main channel area and the floodplain area according to the boundary of the floodplain. Then, a series of discrete water levels are generated for the two areas respectively. The water flow area at each water level is calculated by numerical integration, and the wetted perimeter at each water level is calculated by piecewise summation of the topographic curve length. Finally, the discrete calculation results are transformed into continuous functions of the relationship between the water flow area and water level of the main channel, the water flow area and water level of the floodplain, the wetted perimeter and water level of the main channel, and the water flow area and water level of the floodplain through interpolation or function fitting. This provides standardized hydraulic geometric relationship inputs for subsequent water conveyance capacity calculation and water exchange accounting.

[0055] For cross-sections involving multiple shoals (such as when an island in the river divides the cross-section into a left branch, a right branch, and the island's shoal), the following approach can be used: The cross-section is divided into N sub-regions, each of which includes a main channel sub-region or a floodplain sub-region. For each sub-region i, construct the relationship function between its water-passing area and water level and the relationship function between its wetted perimeter and water level; In the subsequent calculation of the water conveyance capacity function, the water conveyance capacity functions of the main channel sub-regions can be summed to obtain the total main channel water conveyance capacity function, and the water conveyance capacity functions of the floodplain sub-regions can be summed to obtain the total floodplain water conveyance capacity function.

[0056] In step S140, the main channel water conveyance capacity function is obtained based on the relationship function between the main channel water flow area and water level and the relationship function between the main channel wetted perimeter and water level; the floodplain water conveyance capacity function is obtained based on the relationship function between the floodplain water flow area and water level and the relationship function between the floodplain wetted perimeter and water level; and the main channel average flow velocity function is obtained based on the main channel water conveyance capacity function, the floodplain water conveyance capacity function, and the flow rate function of the area to be analyzed.

[0057] The core objective of step S140 is to calculate the water conveyance capacity functions of the main channel and the floodplain based on the hydraulic geometry relationship established in step S130. Furthermore, by combining the total flow process, it aims to solve for the flow distribution between the main channel and the floodplain, as well as the relationship between the average flow velocity of the main channel and time, reflecting the intensity of water movement in the main channel. This provides velocity input for subsequent entrainment exchange volume calculations. This step achieves the transformation from "static hydraulic geometry" to "dynamic hydraulic response," enabling the quantification of the flow share borne by the main channel and the floodplain, as well as the velocity characteristics of the main channel, given a known total flow process.

[0058] According to embodiments of this disclosure, obtaining the main channel water conveyance capacity function based on the relationship function between the main channel's water flow area and water level, and the relationship function between the main channel's wetted perimeter and water level, includes: The main channel water conveyance capacity function is obtained using the following formula. : ; ; The step of obtaining the floodplain water conveyance capacity function based on the relationship function between the floodplain water-passing area and the water level and the relationship function between the floodplain wetted perimeter and the water level includes: The floodplain water conveyance capacity function is obtained using the following formula. : ; ; The step of obtaining the average velocity function of the main channel based on the main channel water conveyance capacity function, the floodplain water conveyance capacity function, and the flow rate function of the area to be analyzed includes: Under the assumption of a uniform water surface slope, the average velocity function of the main channel is obtained by the following formula. : ; ; ; in, This represents the Manning roughness of the main groove, typically ranging from 0.03 to 0.045. This represents the Manning roughness of the floodplain, typically ranging from 0.04 to 0.1. and It can be determined by combining measured data or historical data; This represents a function relating the water flow area of ​​the main channel to the water level. This represents the function relating the wetted perimeter of the main tank to the water level. This represents a function relating the floodplain's surface area to the water level. This represents the function relating the wetted perimeter of the floodplain to the water level. Represents the floodplain flow function. This represents the main tank flow rate function; The flow function representing the water area to be analyzed can be obtained by interpolating daily flow data; water level It changes over time, that is... It can be obtained by interpolating daily water level data.

[0059] When the water level At that time, the floodplain area was not flooded and there was no water exchange.

[0060] In one specific implementation method, taking the Wuguizhou River section in 2016 as an example, based on the bottom sediment and vegetation conditions of the main channel and the floodplain, and combined with on-site investigation, historical data or existing calibration results, the Manning roughness of the main channel was determined to be 0.038 and the Manning roughness of the floodplain was 0.065.

[0061] For cross-sections involving multiple main channel sub-regions (such as branching channels), the following approach can be used: The cross-section is divided into N main channel sub-regions and M floodplain sub-regions; Calculate the water conveyance capacity of each main tank sub-area separately; The total water conveyance capacity of the main channel is the sum of the water conveyance capacities of each main channel sub-area; the flow rate of each main channel sub-area is distributed proportionally to its water conveyance capacity; when calculating the average flow velocity of each main channel sub-area, the flow rate of the main channel sub-area can be divided by the water flow area of ​​the corresponding main channel sub-area.

[0062] In step S150, the start and end time periods of the floodplain hydrological connectivity event are determined based on the water level function and flow function of the water area to be analyzed and the boundary of the floodplain.

[0063] The core objective of step S150 is to automatically identify and extract the occurrence periods of floodplain hydrological connectivity events based on the water level function of the area to be analyzed and the determined floodplain-channel demarcation boundaries. This provides a unified time window for subsequent calculations of water exchange volume and connectivity at the event scale. This step solves the problem of how to objectively delineate "events" from a continuous hydrological sequence, enabling subsequent calculations to be performed within physically meaningful time periods, rather than simply based on fixed calendar periods, thus more realistically reflecting the intermittent characteristics of floodplain connectivity.

[0064] The occurrence of floodplain hydrological connectivity events is closely related to whether the water level exceeds the lower edge of the floodplain. When the water level rises above the lower edge of the floodplain, water begins to enter the floodplain, and water exchange occurs between the floodplain and the channel; when the water level falls back below the lower edge of the floodplain, the floodplain is exposed, and water exchange between the floodplain and the channel ceases. Therefore, a floodplain hydrological connectivity event can be defined as a period in which the water level is continuously higher than the lower edge of the floodplain, and its start and end times are determined by the intersection of the water level hydrograph and the water level at the lower edge of the floodplain. The start time of the event is... The moment when the water level first rises from below the lower edge of the floodplain to above the lower edge of the floodplain, and the moment when the event ends. The start and end time of the floodplain hydrological connectivity event is defined as the moment when the water level first falls from above the lower edge of the floodplain to below it. For complex hydrological processes (such as multiple rises and falls), by traversing the entire water level sequence, multiple independent floodplain hydrological connectivity events can be identified, with each event corresponding to a complete "rise-floodplain-receding" process.

[0065] Furthermore, based on the peak time, floodplain hydrological connectivity events can be divided into a rising phase and a receding phase. The rising phase is when the water level rises from... Rise to the highest point time period The receding section is when the water level drops from its highest point. Falling back to time period .

[0066] In the specific implementation of this step, the water level function and flow function of the water area to be analyzed are first obtained. Based on the daily water level observation data of hydrological stations within or near the water area to be analyzed, the discrete water level time series can be transformed into a continuous water level function through interpolation. When measured water level data is lacking, the corresponding water level process can be calculated from the known flow process data based on the water level-flow relationship curve of the water area. At the same time, based on the daily flow observation data of hydrological stations within or upstream and downstream of the water area to be analyzed, the discrete flow time series can be transformed into a continuous flow function through interpolation. When measured flow data is lacking, it can be obtained from the results of hydrological model simulation, historical flood survey data, or by back-calculation from water level data combined with the water level-flow relationship curve. Subsequently, based on the water level function of the water area to be analyzed and the boundary of the floodplain and channel, the moment when the water level first exceeds the lower edge of the floodplain is identified as the start time of the event, and the moment when the water level last falls back below the lower edge of the floodplain is identified as the end time of the event, thereby extracting the start and end time periods corresponding to each continuous floodplain state as independent floodplain hydrological connectivity events. On this basis, combined with the flow function, a unified time window can be provided for the calculation of water exchange volume at the subsequent event scale.

[0067] In step S160, based on the start and end time periods of the floodplain hydrological connectivity event and the relationship function between the floodplain water flow area and the water level, the volume of water storage and drainage exchange driven by water level fluctuations in the floodplain hydrological connectivity event is calculated; based on the start and end time periods of the floodplain hydrological connectivity event and the average flow velocity function of the main channel, the volume of entrainment exchange dominated by secondary flow in the floodplain hydrological connectivity event is calculated.

[0068] The core objective of step S160 is to calculate the exchange volume of floodplain water driven by two different physical mechanisms, based on the identified floodplain hydrological connectivity events: the floodplain surface storage and drainage exchange volume driven by water level fluctuations and the entrainment exchange volume dominated by secondary currents. This provides the numerator input for the final construction of a dimensionless hydrological connectivity index. This step represents a crucial leap from "event identification" to "exchange quantification," transforming the abstract concept of "hydrological connectivity" into a calculable and accumulative concrete physical quantity.

[0069] The implementation principle of this step is based on a deep understanding of two driving mechanisms: the water level fluctuation mechanism and the secondary flow-dominated mechanism. For the water level fluctuation mechanism, during a floodplain event, as the water level rises, the floodplain's surface area increases, and water accumulates on the surface; as the water level recedes, the floodplain's surface area decreases, and water is discharged from the surface. This storage and discharge process forms a water exchange between the floodplain and the channel. The exchange flow per unit distance is equal to the time rate of change of the floodplain's surface area. Integrating along the river length and accumulating the total flow over the entire event period yields the storage and discharge exchange volume. For the secondary flow-dominated mechanism, at the floodplain-channel interface, due to the velocity difference between the main channel and the floodplain, a transverse shear layer and its associated secondary flow and vortex structures are formed, causing water from the main channel to continuously entrain into the floodplain and be transported back. The volumetric exchange flux per unit interface length is proportional to the average velocity of the main channel and the characteristic water depth at the interface. Integrating along the interface length and accumulating the total flow over the entire event period yields the entrainment exchange volume. The two mechanisms together determine the scale and intensity of water exchange between the beach and the channel. The cumulative exchange volume of the event is obtained by summing the results after calculating them separately.

[0070] According to embodiments of this disclosure, calculating the floodplain water storage and drainage exchange volume driven by water level fluctuations during the floodplain hydrological connectivity event, based on the start and end times of the floodplain hydrological connectivity event and the relationship function between the floodplain water area and water level, includes: The relationship between the floodplain's flooded area and water level is expressed as a function. Differentiating with respect to time yields the time-varying function of the floodplain's surface area. The time-varying surface area of ​​the floodplain is used to characterize the unit flow rate along the flow path, and the specific formula is as follows: ; Based on the time variation function of the floodplain's water surface The effective length of the water area to be analyzed Calculate the volume of water storage and drainage exchange on the floodplain driven by water level fluctuations during the floodplain hydrological connectivity event, taking into account the start and end times of the event. Specifically, the unit flow rate along the effective length of the water body is integrated to obtain the instantaneous total flow rate; then, it is integrated over the entire event period to obtain the surface water storage and drainage exchange volume. The specific formula is as follows: ; If we calculate the volume of water storage and drainage exchange on the floodplain surface during the rising phase of the floodplain hydrological connectivity event, respectively... and the volume of water storage and drainage exchanged on the receding beach. It can be obtained through the following formula: ; ; The step of calculating the entrainment exchange volume dominated by secondary currents in the floodplain hydrological connectivity event based on the start and end times of the event and the average velocity function of the main channel includes: According to the average flow velocity function of the main channel Characteristic water depth at the boundary between the shoal and channel and preset suction coefficient Construct a unit interface length volume exchange flux function The specific formula is as follows: ; Among them, the preset suction coefficient The value can be selected or calibrated based on the vegetation conditions of the beach, the velocity ratio, and the relative water depth. If no calibration data is available, a recommended initial value in the range of 0.01–0.05 can be selected, and a sensitivity test can be performed on k to obtain a robust interval.

[0071] Furthermore, based on the unit interface length volume exchange flux function and the length of the boundary of the beach and channel. Constructing an instantaneous exchange flow function The specific formula is as follows: = ; Finally, based on the instantaneous exchange flow function Calculate the entrainment exchange volume dominated by secondary currents during the floodplain hydrological connectivity event, based on the start and end times of the event. The specific formula is as follows: = ; If we calculate the entrainment and exchange volume of the rising section dominated by secondary currents in the aforementioned floodplain hydrological connectivity events, and the volume exchanged by entrainment in the fading segment It can be obtained through the following formula: = ; = ; In one specific implementation, taking the Wuguizhou River section in 2016 as an example, the effective length of the representative river section and the length of the boundary between the floodplain and the channel are both 4.62 km.

[0072] In step S170, the floodplain hydrological connectivity of the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

[0073] The core objective of step S170 is to construct a dimensionless floodplain hydrological connectivity index based on the floodplain water storage and drainage exchange volume and entrainment exchange volume calculated in step S160, combined with the total water flow volume during the event period. This enables a quantitative characterization and horizontal comparison of the intensity of floodplain hydrological connectivity events. This step completes the transformation from "absolute exchange volume" to "relative connectivity intensity," allowing for comparison of connectivity effects between flood events of different scales and between different river sections at the same scale.

[0074] The principle behind this step is based on the following understanding: While the absolute exchange volume of a floodplain hydrological connectivity event reflects the total amount of water exchange between the floodplain and the channel, this value is significantly affected by the event scale (such as flood size and duration)—large flood events are usually accompanied by larger exchange volumes, but this does not necessarily mean higher "connectivity efficiency." To eliminate the influence of event scale and achieve horizontal comparison between different events, this disclosure normalizes the exchange volume. The normalization benchmark is chosen as the total water volume passing through the cross-section during the event, which reflects the total water volume of the event. Dividing the cumulative exchange volume by the total water volume yields the dimensionless floodplain-channel hydrological connectivity. The physical meaning of this ratio is that the water exchange volume occurring per unit water volume reflects the "connectivity efficiency" of the flow rather than just the "connectivity scale," thus realizing the conversion from absolute exchange volume to relative connectivity intensity. This constructs a dimensionless floodplain-channel hydrological connectivity index that can be horizontally compared between different river sections and different events, providing a unified quantitative tool for river and lake shoreline ecological assessment and engineering management.

[0075] According to embodiments of this disclosure, the step of calculating the floodplain hydrological connectivity of the floodplain hydrological connectivity event based on the start and end times of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed includes: The water storage and drainage exchange volume of the beach surface and the entrainment exchange volume The sum is the cumulative exchange volume of the aforementioned floodplain hydrological connectivity events. ,Right now: .

[0076] If we calculate the cumulative exchange volume of the rising segment of the floodplain hydrological connectivity event separately... Cumulative exchange volume of the receding segment It can be obtained through the following formula: ; ; Based on the start and end times of the floodplain hydrological connectivity event and the flow function of the water area to be analyzed. Calculate the total water volume of the floodplain hydrological connectivity event. The specific formula is as follows: ; If we calculate the total water volume of the rising section of the floodplain hydrological connectivity event separately... Total water volume of the receding section It can be obtained through the following formula: ; ; Based on the cumulative exchange volume and the total water volume of the water area Calculate the floodplain-channel hydrological connectivity of the floodplain hydrological connectivity event. The specific formula is as follows: ; If we calculate the hydrological connectivity of the floodplain in the rising section of the floodplain hydrological connectivity event separately... and hydrological connectivity of the receding section of the channel It can be obtained through the following formula: ; ; Beach-channel hydrological connectivity It has the following mathematical meaning: if and only if there is no water exchange =0; when A value less than 1 indicates that the exchange volume does not exceed the total water flow volume; The larger the value, the stronger the water exchange between the shoal and channel occurs per unit volume of water.

[0077] Finally, the calculated hydrological connectivity of the floodplain can be used to... The event information (event number, start and end time, peak water level, etc.) is recorded together as the hydrological connectivity quantification result of the event.

[0078] In addition, based on event-scale floodplain hydrological connectivity, multi-scale floodplain hydrological connectivity can be further constructed.

[0079] Figure 5 A flowchart illustrating another method for calculating the hydrological connectivity between floodplains and main channels according to an embodiment of this disclosure is shown. Figure 5 As shown, the method further includes the following steps S180~S190: In step S180, the multi-scale floodplain hydrological connectivity corresponding to one or more floodplain hydrological connectivity events occurring during the proposed analysis period is obtained; the multi-scale floodplain hydrological connectivity includes one or more of the following: annual scale floodplain hydrological connectivity, monthly scale floodplain hydrological connectivity, and daily scale floodplain hydrological connectivity.

[0080] When the proposed analysis period is a specified day, the corresponding multi-scale channel hydrological connectivity is the daily-scale channel hydrological connectivity; when the proposed analysis period is a specified month, the corresponding multi-scale channel hydrological connectivity is the monthly-scale channel hydrological connectivity; when the proposed analysis period is a specified year, the corresponding multi-scale channel hydrological connectivity is the annual-scale channel hydrological connectivity.

[0081] Among them, the daily-scale floodplain hydrological connectivity is used to finely depict the continuous changes in floodplain hydrological connectivity over time with a daily time resolution, providing time-aligned connectivity input for correlation analysis with daily ecological observation data (such as vegetation index, bird activity, water quality monitoring, etc.); the monthly-scale floodplain hydrological connectivity is used to reveal the seasonal variation patterns of river and lake floodplain hydrological connectivity with a monthly time unit, identify the differences in connectivity characteristics between the wet and dry seasons, and provide intermediate-scale connectivity information for monthly ecological process analysis and engineering scheduling scheme optimization; the annual-scale floodplain hydrological connectivity is used to quantify the overall hydrological connectivity intensity between the river and lake floodplain and the main channel within a complete year on a macro scale, providing a comprehensive indicator for assessing the annual ecological health status, analyzing interannual variation trends, and supporting long-term engineering scheduling decisions.

[0082] For the specific implementation of daily-scale channel-shoal hydrological connectivity: Floodplain hydrological connectivity events are distributed continuously over time, but the intensity of water exchange within each event is not uniformly distributed. To obtain the daily connectivity intensity, the total exchange volume and total flow volume calculated at the event scale need to be further decomposed into each day.

[0083] In practical implementation, firstly, based on daily water level data, it is determined whether a day is in a floodplain state. For dates within the floodplain event period, the cumulative exchange volume of all events on that day (which can be obtained by summing the surface storage-discharge exchange volume and entrainment exchange volume on that day) and the total water volume flowing through the water area on that day (calculated by multiplying the flow function by the duration of that day) are obtained. Then, the ratio of the cumulative exchange volume connectivity intensity to the total water volume flowing through the water area on that day is taken as the daily-scale floodplain-channel hydrological connectivity for that day. For dates not within any floodplain event period, the connectivity is set to zero. By traversing all dates throughout the year, the daily-scale floodplain-channel hydrological connectivity sequence can be obtained.

[0084] For the specific implementation of monthly-scale flood-channel hydrological connectivity: Monthly-scale floodplain hydrological connectivity is an intermediate time scale between daily and annual scales. It can reflect seasonal variation characteristics and is more stable and comprehensive than daily scale.

[0085] In practice, firstly, based on the generated daily-scale connectivity sequence, the set of dates included in a given month is determined, and the daily cumulative exchange volume and daily total water volume of all dates within that month are obtained. Then, the cumulative exchange volumes of all dates within the month are summed to obtain the monthly cumulative exchange volume, and the total water volume of all dates is summed to obtain the monthly total water volume of the water body. Finally, the ratio of the monthly cumulative exchange volume to the monthly total water volume of the water body is taken as the monthly-scale channel-float hydrological connectivity for that month. Repeating the above process for all 12 months of the year yields the monthly-scale channel-float hydrological connectivity sequence for each month of the year.

[0086] For the specific implementation of annual-scale channel-shoal hydrological connectivity: The annual floodplain hydrological connectivity consists of several independent floodplain events, each with different scales and exchange intensities.

[0087] In practice, firstly, all floodplain hydrological connectivity events, totaling N events, are identified within the calculation year. For the j-th event, its cumulative exchange volume and total water passage volume are obtained. Then, the cumulative exchange volumes of all events throughout the year are summed to obtain the annual total exchange volume, and the total water passage volumes of all events are summed to obtain the annual total water passage volume. Finally, the ratio of the annual total exchange volume to the annual total water passage volume is taken as the annual floodplain hydrological connectivity. Repeating the above process for each of the 12 months of the year yields the monthly floodplain hydrological connectivity sequence.

[0088] Furthermore, the j-th floodplain hydrological connectivity event can be divided into a rising phase and a receding phase based on the peak water level time, and the hydrological connectivity of the rising phase and the receding phase can be calculated separately. On this basis, the annual-scale hydrological connectivity of the rising phase and the annual-scale hydrological connectivity of the receding phase can be summarized annually to characterize the phased differences in floodplain-channel hydrological connectivity within the year.

[0089] The core purpose of dividing the connectivity between the rising and receding phases is to reveal the differences in water exchange characteristics between the rising and receding phases during floodplain hydrological connectivity, quantify the asymmetry between the floodplain filling and drainage processes, and provide a phased analysis tool for a deeper understanding of the dynamic mechanism and ecological response process of floodplain hydrological connectivity.

[0090] When calculating the hydrological connectivity of the rising segment in the j-th floodplain hydrological connectivity event, the cumulative exchange volume of the rising segment and the total water volume of the rising segment are first calculated. Then, the ratio of the cumulative exchange volume of the rising segment to the total water volume of the rising segment is taken as the hydrological connectivity of the rising segment in the j-th floodplain hydrological connectivity event.

[0091] When calculating the annual scale hydrological connectivity of the rising segment for a specified year, the cumulative exchange volume of the rising segment for all events throughout the year is first summed to obtain the total cumulative exchange volume of the rising segment for the year. Then, the total water volume of the rising segment for all events throughout the year is summed to obtain the total water volume of the rising segment for the year. Finally, the ratio of the total cumulative exchange volume of the rising segment to the total water volume of the rising segment for the year is taken as the annual scale hydrological connectivity of the rising segment for the specified year.

[0092] When calculating the hydrological connectivity of the receding section in the j-th floodplain hydrological connectivity event, the cumulative exchange volume and the total water volume flowing through the receding section are first calculated. Then, the ratio of the cumulative exchange volume and the total water volume flowing through the receding section is taken as the hydrological connectivity of the receding section in the j-th floodplain hydrological connectivity event.

[0093] When calculating the annual-scale hydrological connectivity of the receding section for a specified year, the cumulative exchange volume of the receding section for all events throughout the year is first summed to obtain the total cumulative exchange volume of the receding section for the year. Then, the total water volume of the receding section for all events throughout the year is summed to obtain the total water volume of the receding section for the year. Finally, the ratio of the total cumulative exchange volume of the receding section for the year to the total water volume of the receding section for the year is taken as the annual-scale hydrological connectivity of the receding section for the specified year.

[0094] By comparing the annual-scale connectivity during the rising phase with that during the receding phase and their ratio, the phased differences in hydrological connectivity between the floodplain and the channel within the year can be quantitatively characterized.

[0095] In step S190, based on the multi-scale floodplain hydrological connectivity and / or the floodplain hydrological connectivity of each floodplain hydrological connectivity event occurring during the proposed analysis period, a sequence of floodplain hydrological connectivity change characteristics during the proposed analysis period is statistically generated.

[0096] In the specific implementation of step S190, statistical characteristic analysis can be performed on all floodplain hydrological connectivity events within the proposed analysis period based on the generated multi-scale connectivity sequence, including the total number of events, maximum connectivity, average connectivity, and connectivity variation coefficient. At the same time, the connectivity contribution of each event during the water level rise and receding phases can be calculated separately, and the asymmetric characteristics of the floodplain filling and drainage process can be revealed by the ratio of connectivity during the rise and receding phases. Finally, the above statistical results are organized in chronological order to form a floodplain hydrological connectivity change characteristic sequence within the proposed analysis period, providing a quantitative basis for subsequent ecological response analysis and engineering management.

[0097] In one specific implementation, taking the Wuguizhou River section as an example and 2016 as the calculation period, after completing the hydraulic geometry and roughness parameter settings, under the unified water surface slope assumption, the daily total flow in 2016 is allocated to the main channel and the floodplain, obtaining the daily main channel flow and daily floodplain flow, and further obtaining the daily average velocity sequence of the main channel. Then, the daily water level and daily flow data for 2016 are traversed to identify all floodplain connectivity events and calculate the hydrological connectivity of each event, forming an event-scale connectivity sequence. Furthermore, the event results can be mapped back to the daily time axis: the daily connectivity intensity is given during the event duration, and the connectivity intensity is set to zero during non-floodplain periods, thus forming the daily floodplain-channel hydrological connectivity sequence for 2016; alternatively, the daily connectivity intensity can be accumulated or statistically summarized monthly to form the monthly-scale floodplain-channel hydrological connectivity sequence for 2016. The calculation results of the daily floodplain-channel hydrological connectivity are as follows: Figure 6 As shown.

[0098] In this embodiment, through the above steps S110~190, under the condition of having daily water level-flow data in 2016, the boundary determination of the floodplain and channel of the Wuguizhou River section, the identification of floodplain connectivity events, the calculation of water exchange volume at the event scale, and the construction of daily / monthly / event multi-scale connectivity sequences can be completed. This provides a unified and verifiable calculation framework for subsequent analysis of annual variation patterns, analysis of differences between rising and receding sections, and analysis of the relationship with vegetation response.

[0099] The technical solution disclosed herein transforms the complex hydrological connectivity problem of river and lake floodplains into an analytical computational problem based on cross-sectional topography and hydrological processes by constructing a computational framework of "hydraulic-driven decomposition - process separation and accounting - volume normalization". This framework enables floodplain-channel diversion calculations to be completed even when conditions are unavailable or inconvenient for developing three-dimensional numerical models, utilizing readily available cross-sectional topography, water level, and flow data. It quantifies the floodplain storage and drainage exchange volume driven by water level fluctuations and the entrainment exchange volume dominated by secondary flows, thereby constructing a dimensionless hydrological connectivity index that can be analyzed over long-term series and compared laterally. This solves the problems in existing technologies, such as the difficulty in stably obtaining the main channel and floodplain flow distribution results under known total flow conditions, the difficulty in further quantifying the scale and intensity of water exchange between floodplains and channels, and the difficulty in forming a hydrological connectivity index at the event scale that can be used for comparison between different river sections and different flood processes. This supports quantitative research on the evolution of river and lake floodplains and the response of habitat processes to hydrological changes, and provides a reliable technical basis for floodplain management, ecological restoration, and engineering scheduling.

[0100] Figure 7 A structural block diagram of a device for calculating the hydrological connectivity of a river / lake floodplain and main channel according to an embodiment of this disclosure is shown. Figure 7As shown, the hydrological connectivity calculation device for the river and lake floodplain and main channel includes: a floodplain-channel boundary delineation module, configured to: acquire characteristic cross-sectional topographic data of the area to be analyzed; calculate the floodplain-channel delineation boundary of the area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data; and a floodplain-channel hydrological parameter calculation module, configured to: construct the main channel flow area versus water level function, the floodplain flow area versus water level function, the main channel wetted perimeter versus water level function, and the floodplain wetted perimeter versus water level function based on the characteristic cross-sectional topographic data and the floodplain-channel delineation boundary; obtain the main channel water conveyance capacity function based on the main channel flow area versus water level function and the main channel wetted perimeter versus water level function; obtain the floodplain water conveyance capacity function based on the floodplain flow area versus water level function and the floodplain wetted perimeter versus water level function; and obtain the floodplain water conveyance capacity function based on the main channel water conveyance capacity function, The average velocity function of the main channel is obtained from the floodplain water conveyance capacity function and the flow function of the water area to be analyzed; the start and end time periods of the floodplain hydrological connectivity event are determined according to the water level function and flow function of the water area to be analyzed and the floodplain-channel division boundary; the floodplain hydrological connectivity event's surface water storage and drainage exchange volume driven by water level fluctuations is calculated according to the floodplain hydrological connectivity event's start and end time periods and the floodplain water area-water level relationship function; the floodplain hydrological connectivity event's entrainment exchange volume dominated by secondary flow is calculated according to the floodplain hydrological connectivity event's start and end time periods and the main channel average velocity function; the floodplain-channel hydrological connectivity calculation module is configured to: calculate the floodplain-channel hydrological connectivity of the floodplain hydrological connectivity event based on the floodplain hydrological connectivity event's start and end time periods, the floodplain water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

[0101] Figure 8 A structural block diagram of another device for calculating the hydrological connectivity of floodplains and main channels according to an embodiment of this disclosure is shown. Figure 8 As shown, the hydrological connectivity calculation device between the river / lake floodplain and the main channel also includes: The multi-scale floodplain hydrological connectivity calculation module is configured to: obtain the multi-scale floodplain hydrological connectivity corresponding to one or more floodplain hydrological connectivity events occurring during the proposed analysis period; the multi-scale floodplain hydrological connectivity includes one or more of the following: annual scale floodplain hydrological connectivity, monthly scale floodplain hydrological connectivity, and daily scale floodplain hydrological connectivity; the floodplain hydrological connectivity change feature sequence generation module is configured to: statistically generate a floodplain hydrological connectivity change feature sequence within the proposed analysis period based on the multi-scale floodplain hydrological connectivity and / or the floodplain hydrological connectivity of each floodplain hydrological connectivity event occurring during the proposed analysis period.

[0102] This disclosure also provides an electronic device, Figure 9 A structural block diagram of an electronic device according to an embodiment of the present disclosure is shown, such as... Figure 9As shown, the electronic device includes a memory and a processor; wherein the memory is used to store one or more computer instructions, wherein the one or more computer instructions are executed by the processor to implement the method described in any of the above method embodiments.

[0103] This disclosure also provides a computer-readable storage medium, which may be a computer-readable storage medium included in the electronic device or computer system described in the above embodiments; or it may be a standalone computer-readable storage medium not assembled into a device. The computer-readable storage medium stores one or more programs, which are used by one or more processors to perform the methods described in this disclosure.

[0104] This disclosure also provides a computer program product, including a computer program that, when executed by a processor, implements any of the methods described in this disclosure.

[0105] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

Claims

1. A method for calculating the hydrological connectivity between river / lake floodplains and main channels, characterized in that, include: Obtain characteristic cross-sectional topographic data of the water area to be analyzed; Based on the characteristic cross-sectional topographic data, the boundary of the shoal and channel in the area to be analyzed is calculated using the hydraulic depth objective function method; Based on the characteristic cross-sectional topographic data and the floodplain boundary, construct the following functions: the relationship between the main channel's water-passing area and water level, the relationship between the floodplain's water-passing area and water level, the relationship between the main channel's wetted perimeter and water level, and the relationship between the floodplain's wetted perimeter and water level. The main channel water conveyance capacity function is obtained based on the relationship function between the main channel water flow area and water level and the relationship function between the main channel wetted perimeter and water level; the floodplain water conveyance capacity function is obtained based on the relationship function between the floodplain water flow area and water level and the floodplain wetted perimeter and water level. The average velocity function of the main channel is obtained based on the water conveyance capacity function of the main channel, the water conveyance capacity function of the floodplain, and the flow rate function of the area to be analyzed. Based on the water level function and flow function of the water area to be analyzed and the boundary of the floodplain, the start and end time periods of the floodplain hydrological connectivity event are determined. Based on the start and end times of the floodplain hydrological connectivity event and the relationship function between the floodplain water flow area and the water level, calculate the floodplain surface water storage and drainage exchange volume driven by water level fluctuations during the floodplain hydrological connectivity event. Based on the start and end times of the floodplain hydrological connectivity event and the average flow velocity function of the main channel, calculate the entrainment exchange volume dominated by secondary flow in the floodplain hydrological connectivity event. The floodplain hydrological connectivity of the floodplain hydrological connectivity event is calculated based on the start and end times of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

2. The method according to claim 1, characterized in that, The characteristic cross-section topographic data includes multiple sets of characteristic cross-section topographic data corresponding to multiple characteristic cross-sections. Each set of characteristic cross-section topographic data includes multiple sets of measuring point data for the corresponding characteristic cross-section. Each set of measuring point data includes the distance between measuring points distributed along the horizontal direction of the cross-section and the elevation value corresponding to the distance between the measuring points. The step of calculating the floodplain / channel delineation boundary of the area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data includes: For any given characteristic cross section, based on the corresponding topographic data of the characteristic cross section, the water level boundary between the floodplain and the main channel of the given characteristic cross section is calculated using the hydraulic depth objective function method. The boundary between the floodplain and the main channel of the water level is determined based on the water level boundary point of each characteristic cross section.

3. The method according to claim 2, characterized in that, The calculation of the water level boundary between the floodplain and the main channel of any characteristic cross-section based on the corresponding characteristic cross-section topographic data, using the hydraulic depth objective function method, includes: Based on the corresponding characteristic cross-section topographic data, calculate the water-passing area and water-passing width of any characteristic cross-section at the preset water level; Based on the water passage area and the water passage width, calculate the hydraulic depth of any characteristic cross section at the preset water level; Based on the water passage width and the preset water level change step size, the central difference method is used to calculate the growth rate of the water passage width with respect to the water level. Based on the growth rate of the water level with respect to the water passage width and the hydraulic depth, a hydraulic depth objective function is constructed; The elevation value of the measuring point at the lower edge of the floodplain of any characteristic cross section is determined based on the water level corresponding to the maximum value of the hydraulic depth objective function, and the elevation value of the measuring point at the lower edge of the floodplain is used as the water level boundary between the floodplain and the main channel of any characteristic cross section.

4. The method according to claim 1, characterized in that, The step of obtaining the main channel water conveyance capacity function based on the relationship function between the main channel's water flow area and water level, and the relationship function between the main channel's wetted perimeter and water level, includes: The main channel water conveyance capacity function is obtained using the following formula. : ； ； The step of obtaining the floodplain water conveyance capacity function based on the relationship function between the floodplain water-passing area and the water level and the relationship function between the floodplain wetted perimeter and the water level includes: The floodplain water conveyance capacity function is obtained using the following formula. : ； ； The step of obtaining the average velocity function of the main channel based on the main channel water conveyance capacity function, the floodplain water conveyance capacity function, and the flow rate function of the area to be analyzed includes: The average flow velocity function of the main channel is obtained by the following formula. : ； ； in, Indicates the Manning roughness of the main groove. Indicates the roughness of the floodplain Manning. This represents a function relating the water flow area of ​​the main channel to the water level. This represents the function relating the wetted perimeter of the main tank to the water level. This represents a function relating the floodplain's surface area to the water level. This represents the function relating the wetted perimeter of the floodplain to the water level. This represents the flow function of the water area to be analyzed.

5. The method according to claim 1, characterized in that, The step of calculating the floodplain water storage and drainage exchange volume driven by water level fluctuations during the floodplain hydrological connectivity event, based on the start and end times of the event and the relationship function between the floodplain water area and water level, includes: The time variation function of the floodplain's water-passing area is obtained by differentiating the function of the relationship between the floodplain's water-passing area and the water level with respect to time. Based on the time variation function of the floodplain water surface, the effective length of the water area to be analyzed, and the start and end time of the floodplain hydrological connectivity event, calculate the floodplain surface water storage and drainage exchange volume driven by water level fluctuations in the floodplain hydrological connectivity event. The step of calculating the entrainment exchange volume dominated by secondary currents in the floodplain hydrological connectivity event based on the start and end times of the event and the average velocity function of the main channel includes: Construct a volume exchange flux function per unit interface length based on the average flow velocity function of the main channel, the characteristic water depth at the boundary of the shoal and channel division, and the preset entrainment coefficient. Construct an instantaneous exchange flow function based on the unit interface length volume exchange flux function and the length of the beach-channel boundary; The entrainment exchange volume dominated by secondary flow in the floodplain hydrological connectivity event is calculated based on the instantaneous exchange flow function and the start and end time periods of the floodplain hydrological connectivity event.

6. The method according to claim 1, characterized in that, The calculation of the floodplain hydrological connectivity degree of the floodplain hydrological connectivity event based on the start and end time periods of the floodplain hydrological connectivity event, the floodplain surface water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed includes: The sum of the surface water storage and drainage exchange volume and the entrainment exchange volume is taken as the cumulative exchange volume of the floodplain hydrological connectivity event. The total water volume of the floodplain hydrological connectivity event is calculated based on the start and end times of the event and the flow function of the water area to be analyzed. The floodplain hydrological connectivity of the floodplain hydrological connectivity event is calculated based on the cumulative exchange volume and the total water flow volume of the water area.

7. The method according to claim 1, characterized in that, The method further includes: Obtain multi-scale floodplain hydrological connectivity corresponding to one or more floodplain hydrological connectivity events occurring during the proposed analysis period; the multi-scale floodplain hydrological connectivity includes one or more of the following: annual scale floodplain hydrological connectivity, monthly scale floodplain hydrological connectivity, and daily scale floodplain hydrological connectivity. Based on the multi-scale floodplain hydrological connectivity and / or the floodplain hydrological connectivity of each floodplain hydrological connectivity event occurring during the proposed analysis period, a sequence of floodplain hydrological connectivity change characteristics is statistically generated during the proposed analysis period.

8. A device for calculating the hydrological connectivity between river / lake floodplains and main channels, characterized in that, include: The beach-channel boundary delineation module is configured to: acquire characteristic cross-sectional topographic data of the water area to be analyzed; and calculate the beach-channel delineation boundary of the water area to be analyzed using the hydraulic depth objective function method based on the characteristic cross-sectional topographic data. The floodplain hydrological parameter calculation module is configured to: construct, based on the characteristic cross-sectional topographic data and the floodplain boundary, a function relating the main channel's water-passing area to water level, a function relating the floodplain's water-passing area to water level, a function relating the main channel's wetted perimeter to water level, and a function relating the floodplain's wetted perimeter to water level; obtain the main channel's water conveyance capacity function based on the main channel's water-passing area to water level and the main channel's wetted perimeter to water level; obtain the floodplain's water conveyance capacity function based on the floodplain's water-passing area to water level and the floodplain's wetted perimeter to water level; and obtain the floodplain's water conveyance capacity function based on the main channel's water conveyance capacity function and the floodplain's water-passing area to water level. The average velocity function of the main channel is obtained from the water capacity function and the flow function of the water area to be analyzed; the start and end time periods of the floodplain hydrological connectivity event are determined based on the water level function and flow function of the water area to be analyzed and the boundary of the floodplain and the channel; the volume of water storage and drainage exchange driven by water level fluctuations in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the relationship function between the floodplain water area and water level; the volume of entrainment exchange dominated by secondary flow in the floodplain hydrological connectivity event is calculated based on the start and end time periods of the floodplain hydrological connectivity event and the average velocity function of the main channel. The floodplain hydrological connectivity calculation module is configured to calculate the floodplain hydrological connectivity of the floodplain hydrological connectivity event based on the start and end time period of the floodplain hydrological connectivity event, the floodplain water storage and drainage exchange volume, the entrainment exchange volume, and the flow function of the water area to be analyzed.

9. An electronic device, characterized in that, It includes a memory and a processor; the memory is used to store computer instructions, wherein the computer instructions are executed by the processor to implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing computer instructions thereon, characterized in that, When the computer instructions are executed by the processor, they implement the method of any one of claims 1 to 7.

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