A comprehensive unit line improvement method applicable to urbanized areas

Abstract

This invention relates to the field of urban hydrological simulation and flood forecasting technology, specifically disclosing an improved integrated unit flow method applicable to urbanized areas, comprising the following steps: S1, constructing an urban stormwater runoff generation and confluence model to simulate the flow process at the watershed outlet section under design storms with different return periods; S2, calculating the flow process at the watershed outlet section under the same design storm and reconstructing it into a concentrated flow process; S3, allocating the concentrated flow process into sub-flows at drainage outlets and river segments; S4, based on the actual maximum discharge capacity of the drainage outlets, implementing storage and discharge response corrections on the sub-flow processes at the drainage outlets to form a time-series flow process considering drainage capacity constraints; S5, calculating the propagation time delay for the segmented delay of the corrected flow to obtain the improved total flow process; This invention achieves improved simulation of urban stormwater watershed outlet flow by performing spatiotemporal reconstruction, spatial allocation, drainage capacity constraint correction, and propagation time delay on the flow process.

Description

Technical Field

[0001] This invention relates to the field of urban hydrological simulation and flood forecasting technology, and more specifically to an improved integrated unit line method applicable to urbanized areas. Background Technology

[0002] The composite unit hydrograph method, based on Sherman's unit hydrograph theory and incorporating climatic conditions, geographical features, and underlying surface conditions, is a comprehensive empirical parameterization scheme developed through the analysis of extensive measured hydrological data. This method typically establishes empirical relationships between watershed characteristics and key elements of the unit hydrograph, enabling the direct derivation of the applicable unit hydrograph for the watershed based on readily available geographical parameters, and subsequently, the derivation of the flow process at the watershed outlet. The composite unit hydrograph method significantly reduces the difficulty and cost of hydrological analysis in data-scarce areas. Engineers can obtain design flood processes that meet engineering design requirements without constructing complex physical models, playing a crucial role in the planning and design of dikes, reservoirs, bridges, and culverts in small and medium-sized watersheds.

[0003] However, the rapid urbanization process in recent years is profoundly reshaping the hydrological nature of watersheds. On the one hand, large-scale land development and utilization have led to the drastic replacement of natural underlying surfaces with impermeable materials, significantly altering the rainfall-runoff conversion mechanism. On the other hand, the construction of high-density drainage pipe networks has completely restructured the runoff pathways of watersheds, transforming the traditional runoff process, dominated by slope runoff and natural river evolution, into a rapid response mode dominated by pipe network transport. Against this backdrop, whether the unit hydrographs constructed using the integrated unit hydrograph method are still applicable to highly urbanized areas has become a critical issue that urgently needs to be addressed in engineering practice. Faced with this challenge, although modern mathematical models such as SWMM and the MIKE series can construct refined urban runoff generation and runoff simulation systems, thereby improving the accuracy and adaptability of flood calculations, these models have extremely high requirements for data integrity and accuracy during construction, thus facing significant timeliness and cost challenges in practical engineering applications. Therefore, how to improve the integrated unit hydrograph method without relying on high-precision, full-element modeling, so that it can adapt to the complex runoff generation and runoff processes of highly urbanized watersheds, has become an important research direction in the field of urban hydrological simulation. To address the insufficient applicability of the integrated unit hydrograph method in highly urbanized areas, Ma Xumin et al. proposed two improvement schemes based on the Jingtian watershed in Shenzhen (Ma Xumin, Lin Kairong, Guo Weijian, et al. Evaluation and correction of the integrated unit hydrograph method in Guangdong Province under the background of urbanization [J]. China Rural Water Resources and Hydropower, 2024, (01): 142-149.): one is to optimize the parameter settings by calibrating the unit hydrograph lag time and average after-loss rate, and the other is to correct the shape of the unit hydrograph by using the constrained least squares method combined with grid search and cross-validation. Both of the above methods have improved the model simulation accuracy to a certain extent, making the unit hydrograph closer to the characteristics of urban runoff generation and confluence. However, the improved methods still rely heavily on high-quality rainfall and flood data, making them difficult to apply to areas with insufficient data or complex rainfall processes. Moreover, their research mainly focuses on the parameter optimization of traditional runoff generation and confluence processes, and still lacks systematic research on the changes in the confluence process mechanism caused by drainage network constraints and changes in water flow propagation characteristics under the background of urbanization. Summary of the Invention

[0004] The purpose of this invention is to provide an improved integrated unit flow method applicable to urbanized areas. By reconstructing the flow process in time and space, allocating it spatially, correcting drainage capacity constraints, and delaying propagation time, an improved simulation of the outlet flow of urban stormwater basins can be achieved.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for improving integrated unit line in urbanized areas includes the following steps:

[0007] S1. Based on the basic data of the study area, an urban storm runoff generation and confluence model was constructed to simulate the flow process at the watershed outlet section under design storms with different return periods, serving as the baseline result;

[0008] S2. Calculate the flow process at the outlet section of the watershed under the same design rainstorm, reconstruct it in time and space, and transform it into a centralized flow process;

[0009] S3. Based on the layout of the drainage system, the centralized flow process is spatially allocated to form two types of sub-flow processes: drainage outlets and river sections.

[0010] S4. Based on the actual maximum discharge capacity of the drainage outlet, implement storage and discharge response correction for the sub-flow process of the drainage outlet to form a time-series flow process that considers drainage capacity constraints.

[0011] S5. Calculate the propagation time delay of the pipeline and river from the drainage unit to the watershed outlet, segment the time series flow process, and obtain the improved total flow process after time alignment and superposition.

[0012] Furthermore, S1, based on the basic data of the study area, constructs an urban stormwater runoff generation and confluence model to simulate the flow process at the watershed outlet section under design storms with different return periods, specifically as follows:

[0013] The urban stormwater runoff model includes: a one-dimensional pipe network model MIKE Urban, a one-dimensional river channel model MIKE 11, and a two-dimensional surface runoff model MIKE 21;

[0014] The one-dimensional pipe network model MIKEUrban was constructed using land use data, topographic elevation data, and drainage pipe network data.

[0015] The design storm was input into the one-dimensional pipe network model MIKE Urban and the one-dimensional river channel model MIKE 11 to obtain the overflow node location and overflow process;

[0016] The overflow process is input into the two-dimensional surface runoff model MIKE 21 to simulate the surface water depth, inundation range and surface runoff process;

[0017] By comparing the simulation results of surface water depth, inundation range and surface runoff process with measured data, the parameters of the one-dimensional pipe network model MIKE Urban, the one-dimensional river channel model MIKE 11 and the two-dimensional surface runoff model MIKE 21 were calibrated and verified.

[0018] The design storms with different return periods are input into the calibrated and verified urban storm runoff generation and confluence model, and the flow process data of the watershed outlet section are output.

[0019] Furthermore, the S2 method for obtaining a centralized flow process includes the following steps:

[0020] The unit hydrograph sequence of the watershed was determined using the integrated unit hydrograph method, based on the watershed area, main stream length, water catchment area characteristic parameters, runoff parameters, lag time values, and average after-loss rate of the study area.

[0021] The net rainfall sequence of the designed rainstorm period is convolved with the unit hydrograph sequence to obtain the original flow process at the watershed outlet section.

[0022] Assuming rainfall-runoff is an instantaneous response, the inherent propagation lag of the original flow process is eliminated, and it is reconstructed into a centralized flow process.

[0023] Furthermore, S3 spatially allocates the centralized flow process to form two types of sub-flow processes: drainage outlet and river section, specifically:

[0024] Spatial allocation is based on the physical structural characteristics of the drainage system in the study area; wherein, the physical structural characteristics include: the distribution density of drainage outlets, the total length of drainage pipelines, the distribution density of rivers, and the total length of river channels;

[0025] By quantitatively analyzing the physical structural characteristics of the drainage system, the equivalent weights representing the relative importance of the river confluence path and the drainage outlet confluence path are calculated.

[0026] Based on the equivalent weights, the centralized flow process is divided into the drainage outlet sub-flow process and the river channel sub-flow process according to the weight ratio of each unit of the drainage system.

[0027] Furthermore, the method for obtaining the actual maximum discharge capacity of the drainage outlet in step S4 is as follows:

[0028] Several representative drainage outlets in the study area were selected, and the measured maximum flow of the representative drainage outlets under different return periods of design rainstorms was simulated by a calibrated and verified urban storm runoff generation and confluence model. The sum of the measured maximum flow of the representative drainage outlets was obtained.

[0029] The theoretical maximum total flow rate of representative drainage outlets was calculated based on Manning's formula.

[0030] Furthermore, the formation process of the time-series flow process in S4 is specifically as follows:

[0031] At each calculation moment, determine the relationship between the current flow rate of the sub-flow process at the drainage outlet and its actual maximum discharge capacity;

[0032] Based on the actual release or retention situation, the total amount of water in the retention unit is updated again, and the calculation proceeds to the next time step, ultimately forming a time-series flow process that takes into account drainage capacity constraints.

[0033] Furthermore, the determination of the relationship between the current flow rate of the sub-flow process at the drainage outlet and its actual maximum discharge capacity at each calculation time specifically involves:

[0034] If the flow rate of the sub-flow process at the drain outlet exceeds the actual maximum discharge capacity at the current moment, the excess is stored in a virtual storage unit. At this time, the actual outflow of the drain outlet is limited to its actual maximum discharge capacity and updated to the total amount of water in the storage unit.

[0035] If the flow rate of the sub-flow process at the drainage outlet does not exceed the actual maximum discharge capacity at the current moment, then discharge is carried out at that flow rate and the remaining discharge capacity is calculated; at the same time, the difference between the actual maximum discharge capacity and the current flow rate is calculated; based on the ratio of the current total accumulated water volume to the historical maximum total accumulated water volume, the theoretically releaseable accumulated water volume is calculated; the actual accumulated water release volume is the smaller value between the current remaining discharge capacity and the theoretically releaseable accumulated water volume.

[0036] If the accumulated water is released, the flow rate at a certain moment is equal to the flow rate of the atomic flow process at that moment plus the actual amount of accumulated water released.

[0037] Further, in step S5, the propagation time delay of water flow from each drainage unit to the watershed outlet is calculated, specifically as follows:

[0038] Calculate the average flow velocity inside the drainage outlet and in the river channel, respectively;

[0039] The average length of the drainage pipe is determined based on the total length of the drainage pipe and the distribution density of the drainage outlets. The maximum propagation time of each drainage outlet is calculated by combining the average flow velocity of the drainage outlets.

[0040] The average river length is determined based on the total river length and the river distribution density, and the maximum propagation time of each river is calculated by combining the average river flow velocity.

[0041] Furthermore, S5, the improved process for obtaining the total flow rate, specifically includes:

[0042] The flow process after storage and discharge response correction is regarded as uniformly distributed along the length of the drainage pipeline, and the flow is divided into several segments according to the maximum propagation time and the calculation time step, flowing into the river at different time points;

[0043] After the flow enters the river, the propagation time along the river to the watershed outlet is determined based on the relative position of the drainage outlet on the river.

[0044] All delayed sub-flow processes are aligned and superimposed at the watershed outlet section according to time series to obtain the improved total flow process.

[0045] Furthermore, the flow process after storage and discharge response correction is considered to be uniformly distributed along the length of the drainage pipeline, and the flow is divided into several segments based on the maximum propagation time and the calculation time step. The calculation formula for the flow into the river at different time points is as follows:

[0046]

[0047] In the formula, For drainage outlet After the storage and discharge correction, at time The flow rate value; For the drain outlet Sub-flow process After delay processing, The flow rate flowing into the river at any given time; For drainage outlet The number of sub-flow processes segmented within the pipe, through the drain outlet. The ratio of the maximum propagation time to the calculation time step is determined and rounded up. Assign weighting coefficients to traffic.

[0048] According to specific embodiments provided by the present invention, the present invention has the following technical effects compared to the prior art:

[0049] This invention achieves efficient transformation from dispersed runoff generation to centralized flow processes by combining the unit hydrograph method with spatiotemporal reconstruction technology, ensuring accurate spatiotemporal correspondence between benchmark simulation and simplified calculations. Secondly, spatial allocation is performed based on the drainage system layout, and storage and discharge response corrections are strictly implemented based on the actual maximum discharge capacity of drainage outlets, accurately capturing physical constraints such as drainage bottlenecks and water level caps, making the generated time-series flow processes more consistent with the actual physical mechanisms of urban flooding and drainage. Finally, by calculating the propagation time delays of pipes and rivers separately and performing segmented delays and superposition, the evolution characteristics of water flow in different media are accurately simulated, achieving time alignment of multi-path flow. Overall, this scheme significantly improves the accuracy and physical realism of urban stormwater runoff generation and confluence simulation, providing a more reliable scientific basis for urban flood control and drainage planning and risk assessment. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0051] The following description, in conjunction with the accompanying drawings, further illustrates an improved method for integrated unit lines applicable to urbanized areas according to the present invention;

[0052] Figure 1 This is a schematic diagram of the overall process of the comprehensive unit line improvement method applicable to urbanized areas according to the present invention;

[0053] Figure 2 This is a schematic diagram of the one-dimensional pipeline network model MIKE Urban constructed in the Liede Canal watershed of Guangzhou City in this embodiment of the invention;

[0054] Figure 3 These are schematic diagrams of six design rainstorm processes with different return periods in embodiments of the present invention;

[0055] Figure 4 This is a schematic diagram of the total measured maximum flow of representative drainage outlets in the study area under design rainstorms that occur once every 5, 10, 20, 50, 100, and 200 years, according to embodiments of the present invention.

[0056] Figure 5 This is a comparison diagram of the calculation results of the flow process at the outlet section of the watershed using the integrated unit hydrograph method and the simulation results of the flow process at the outlet section of the watershed using the urban storm runoff generation and confluence model under the design storms with a return period of 5 years, 10 years, 20 years, 50 years, 100 years and 200 years. In the figure, (a) is the design storm with a return period of 200 years, (b) is the design storm with a return period of 100 years, (c) is the design storm with a return period of 50 years, (d) is the design storm with a return period of 20 years, (e) is the design storm with a return period of 10 years, and (f) is the design storm with a return period of 5 years.

[0057] Figure 6 This is a comparison diagram of the calculation results of the flow process at the outlet section of the basin under the design storms of 5 years, 10 years, 20 years, 50 years, 100 years and 200 years in the embodiments of the present invention, and the simulation results of the flow process at the outlet section of the basin by the urban storm runoff generation and confluence model; in the figure, (a) is the design storm of 200 years, (b) is the design storm of 100 years, (c) is the design storm of 50 years, (d) is the design storm of 20 years, (e) is the design storm of 10 years, and (f) is the design storm of 5 years. Detailed Implementation

[0058] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0059] To better understand the purpose, structure, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings.

[0060] Example 1

[0061] like Figure 1 As shown, the present invention provides a comprehensive unit line improvement method applicable to urbanized areas, comprising:

[0062] S1. Based on the basic data of the study area, an urban storm runoff generation and confluence model was constructed to simulate the flow process at the watershed outlet section under design storms with different return periods, serving as the baseline result;

[0063] Specifically, this embodiment involves constructing an urban stormwater runoff model based on the basic data of the study area. This model consists of a three-coupled model, MIKEFLOOD, which comprises a one-dimensional pipe network model (MIKE Urban), a one-dimensional river channel model (MIKE 11), and a two-dimensional surface runoff model (MIKE 21).

[0064] In this embodiment, as Figure 2 As shown, a one-dimensional pipe network model, MIKE Urban, was constructed using land use data, topographic elevation data, and drainage network data of the study area. The design storm was input into the one-dimensional pipe network model MIKE Urban and the one-dimensional river model MIKE 11 to obtain the overflow node locations and overflow process. The overflow process was then input into the two-dimensional surface runoff model MIKE 21 to simulate surface water depth, inundation range, and surface runoff process. Based on the simulation results of inundation depth and inundation range, the constructed urban stormwater runoff generation and distribution model was calibrated and validated. The model parameters were adjusted until the simulation accuracy met the requirements. Model validation was conducted in two ways: first, comparing the spatial distribution of the simulated maximum inundation depth with the locations of historical flooding points; and second, comparing the water level changes at simulated points with the measured water level changes. The one-dimensional pipe network model MIKE Urban, the one-dimensional river model MIKE 11, and the two-dimensional surface runoff model MIKE 21 in this embodiment are all existing technologies and will not be described in detail here.

[0065] After the model is validated, pre-calculated design storms with return periods of 5, 10, 20, 50, 100, and 200 years are input into the model. The flow process data of the watershed outlet section are output through the three-coupled model MIKE FLOOD as the benchmark result for subsequent improvements to the integrated unit hydrograph method.

[0066] S2. The flow process at the outlet section of the watershed under the same design storm is calculated using the integrated unit hydrograph method, and then reconstructed in time and space to transform it into a concentrated flow process.

[0067] This embodiment is specifically as follows:

[0068] Based on the integrated unit hydrograph method, the unit hydrograph of the watershed is calculated using basic watershed data such as watershed area, main stream length, water catchment area characteristic parameters, runoff generation parameters, and average after-loss rate. The unit hydrograph calculation results are shown in the first column of Table 1.

[0069] like Figure 3 As shown, the design return periods for rainstorms are 5 years, 10 years, 20 years, 50 years, 100 years, and 200 years (a total of 6), and the design rainfall pattern is the single-peak Chicago rainfall pattern. The following example, a partial design rainstorm occurring between 8:50 and 9:50 AM with a 100-year return period, serves as a result of this invention's implementation.

[0070] After calculating the unit hydrograph for the watershed, the original flow process at the watershed outlet section is obtained by convolving the net rainfall sequence of the design storm (taking the net rainfall from 8:50 to 9:50 during a 100-year return period as an example) with the unit hydrograph sequence. ,part The calculation results are shown in Table 1.

[0071] The process of obtaining the original flow rate at the outlet section of the watershed Then, the flow process is reconstructed. By assuming that the runoff generated by rainfall has an instantaneous response, that is, all the runoff caused by rainfall at a certain moment immediately flows out of the watershed outlet at that moment, the propagation lag inherent in the synthetic unit hydrograph method no longer exists. A concentrated flow process is formed by the sum of all the net rainfall at a certain moment, which is then added to the rainfall at that moment. The calculation formula is shown in equation (1), and the partial reconstruction results are shown in Table 1:

[0072] (1)

[0073] In equation (1), For the unit line at the 1st A flow sequence at each time step; The length of the unit line; Centralized flow process exist The flow rate at any given moment; Net rainfall sequence for the period exist Net rainfall at any given moment.

[0074] The above process is repeated for each rainfall period, ultimately forming a centralized outflow process line without hysteresis characteristics. This centralized reconstruction process eliminates the fixed time delay embedded in the integrated unit hydrograph method, enabling subsequent propagation time delay calculations based on the actual drainage network and river hydraulic characteristics to be performed independently and accurately, ensuring the consistency and controllability of the entire improved method in time delay handling.

[0075] Table 1. Reconstruction Table of Flow Process Using the Unit Line Method

[0076]

[0077] S3. Based on the layout of the drainage system, the centralized flow process is spatially allocated to form two types of sub-flow processes: drainage outlets and river sections.

[0078] This embodiment is specifically as follows:

[0079] Spatial allocation is based on the physical structural characteristics of the drainage system in the study area, including the distribution density of drainage outlets and the total length of drainage pipelines, as well as the distribution density of rivers and the total length of river channels.

[0080] By quantitatively analyzing the structural characteristics of the drainage system, the equivalent weights representing the relative importance of river confluence paths and drainage outlet confluence paths are calculated. Based on these equivalent weights, the concentrated flow process is divided into drainage outlet sub-flow processes and river sub-flow processes according to the weight proportion of each unit in the drainage system. The calculation can be expressed as follows:

[0081]

[0082] (2)

[0083] In the above formula, For the flow rate process of the drainage outlet; This refers to the sub-flow process of the river channel; Equivalent weights; The distribution density of drainage outlets; The distribution density of the river channels; It is a centralized flow process.

[0084] In some embodiments of the present invention, based on the physical structural characteristics of the drainage system in the study area, the centralized flow process reconstructed in Table 1 is... The process was divided into drainage outlet sub-flow process and river channel sub-flow process, and some results are shown in Table 2.

[0085] Table 2 Adjusted Flow Process Allocation Table

[0086]

[0087] S4. Based on the actual maximum discharge capacity of the drainage outlet, implement storage and discharge response correction for the sub-flow process of the drainage outlet to form a time-series flow process that considers drainage capacity constraints.

[0088] This embodiment is specifically as follows:

[0089] Five representative drainage outlets within the study area were selected, and their measured maximum flows under 5-year, 10-year, 20-year, 50-year, 100-year, and 200-year return period design storms were simulated using an urban storm runoff model. The sum of the measured maximum flows of the representative drainage outlets was obtained. Figure 4 As shown. From Figure 4 It can be seen that the sum of the measured maximum flow rates of these five drainage outlets reaches its maximum value of 19.46 m³ / s under a 50-year design rainstorm. After a 50-year rainstorm, the sum of the measured maximum flow rates... It does not change with the increase of the design storm recurrence period, and the duration of the maximum flow in the drainage outlet increases with the increase of the design storm recurrence period, which confirms the upper limit of the measured maximum flow.

[0090] Next, the theoretical maximum flow rate is calculated based on the basic data of each representative drainage outlet. The calculation formula is shown in equation (3):

[0091] (3)

[0092] In equation (3), The number of selected drain outlets; The flow velocity inside the drain pipe; The cross-sectional area of ​​the drainage pipe. This is the Manning roughness coefficient; The hydraulic radius; The longitudinal slope of the drainage outlet pipe; This refers to the diameter of the drain pipe.

[0093] The ratio of the sum of measured maximum flows to the sum of theoretical maximum flows characterizes the reduction in actual drainage capacity relative to theoretical drainage capacity. For any drainage outlet within the study area, its actual maximum discharge capacity is limited based on this ratio.

[0094] In some embodiments of the present invention, the measured maximum total flow rate is 19.46 m³ / s, and the theoretical maximum total flow rate is... The measured maximum flow rate is 48.01 m³ / s. Therefore, the ratio of the measured maximum flow rate to the theoretical maximum flow rate is 0.4. Based on this ratio, the actual maximum discharge capacity of the 54 drainage outlets in the study area is calculated using equation (3), as shown in Table 3.

[0095] Table 3 Calculation of the actual maximum discharge capacity of each drainage outlet

[0096]

[0097] S5. Calculate the propagation time delay of the pipeline and river from the drainage unit to the watershed outlet, and delay the modified sub-flow process in segments. After time alignment and superposition, the improved total flow process is obtained.

[0098] This embodiment is specifically as follows:

[0099] At each calculation moment, for a given outlet, the relationship between the flow rate of the sub-flow process at the current moment and its actual maximum discharge capacity is first determined.

[0100] If drain outlet If the flow rate of a sub-flow process exceeds the actual maximum discharge capacity at the current moment, the excess water cannot be discharged immediately and is considered as temporary water storage in the virtual retention unit of the drain outlet. At this time, the drain outlet... The actual outflow is limited to its actual maximum discharge capacity, and the newly added water volume during this period is updated to the total water volume in the storage unit, which will be discharged when the subsequent flow rate decreases.

[0101] If drain outlet If the flow rate of a sub-flow process at the current moment is less than or equal to the actual maximum discharge capacity, then the discharge outlet... First, the water is immediately discharged into the river channel at the specified flow rate. Simultaneously, its remaining discharge capacity is calculated, i.e., the difference between the actual maximum discharge capacity and the current flow rate. Based on the ratio of the current total water volume to the historical maximum total water volume, the theoretically releaseable water volume is calculated, as shown in equation (4). The actual water release amount is the smaller of the current remaining discharge capacity and the theoretically releaseable water volume.

[0102]

[0103] In equation (4), For drainage outlet The actual maximum emission capacity; This represents the total water level at the current moment. Total historical water accumulation Maximum value; drain outlet Let be any drainage outlet within the study area.

[0104] Drain After the above-mentioned storage and discharge response correction, the flow rate at a certain moment is equal to the flow rate of the atomic flow process at that moment plus the actual released water volume (if any). After this calculation is completed, the total water volume in the storage unit is updated again according to the actual release or storage situation, and the calculation of the next time step begins, ultimately forming a time-series flow process that considers drainage capacity constraints.

[0105] In this embodiment, the process of calculating the propagation time delay of water flow from each drainage unit to the watershed outlet is as follows:

[0106] The average flow velocity in the drainage outlet and the river channel is calculated based on equation (3); the average length of the drainage pipe is determined according to the total length of the drainage pipe and the distribution density of the drainage outlet, and the maximum propagation time of each drainage outlet is calculated in combination with the average flow velocity of the drainage outlet; the average length of the river channel is determined according to the total length of the river channel and the distribution density of the river channel, and the maximum propagation time of each river channel is calculated in combination with the average flow velocity of the river channel.

[0107] In this embodiment, the sub-flow process after the storage and discharge response correction is segmented and delayed according to the propagation time delay, and then superimposed at the outlet to form the final flow process, specifically:

[0108] The time delay processing of the sub-flow process is to divide the flow value at a certain moment into multiple parts according to the time precision based on the maximum propagation time of each drainage unit in the study area, and allocate them to the corresponding future time nodes.

[0109] The flow process after the storage and discharge response correction is considered to be uniformly distributed along the length of the drainage pipeline. Based on the maximum propagation time and the calculation time step, the flow is divided into several segments that flow into the river at different time points. The calculation method can be expressed as follows:

[0110] (5)

[0111] In equation (5), For drainage outlet After the storage and discharge correction, at time The flow rate value; For the drain outlet Sub-flow process After delay processing, The flow rate flowing into the river at any given time; For drainage outlet The number of sub-flow processes segmented within the pipe, through the drain outlet. The ratio of the maximum propagation time to the calculation time step is determined and rounded up. Assign weighting coefficients to traffic.

[0112] After the flow enters the river channel, it is based on the drainage outlet. Based on its relative position in the river channel, determine its propagation time along the river channel to the watershed outlet, and further delay it as follows:

[0113] (6)

[0114] In equation (6), For drainage outlet exist The flow rate flowing into the river at any given time; For drainage outlet After correction for river propagation time lag, The final discharge process of the drainage outlet formed at the outlet section of the basin at any given moment; This is the river channel propagation delay ratio; This represents the maximum propagation time of the river channel.

[0115] In equation (5), the flow allocation weighting coefficient It is based on the maximum propagation time of each drain outlet. Determined. For example, if the maximum propagation time of a certain drainage outlet... If it is 12 minutes, then , , If the maximum propagation time of a certain drainage outlet If it is 20 minutes, then , , , If the maximum propagation time of a certain drainage outlet If it is 30 minutes, then , , , , Similarly, based on the maximum propagation time of each drainage outlet within the study area... The corresponding flow allocation weight coefficients are calculated, thereby calculating the flow process into the river after delaying all drainage outlets.

[0116] In equation (6), the river channel propagation delay ratio coefficient It is determined based on the relative positions of each drainage outlet on the river channel. For example, if the distance between the location of the drainage outlet flowing into the river and the cross-section at the watershed outlet is exactly half the river length, then... =0.5. Similarly, based on the relative positions of each drainage outlet in the study area along the river channel, the corresponding river propagation delay ratio is calculated. This allows for the calculation of the final discharge process at the watershed outlet section after correction for river propagation delays. The river sub-discharge process is then... Assuming uniform distribution along the river length, the corresponding river propagation delay ratio coefficient is calculated based on their relative positions in the river, resulting in the final river flow process at the basin outlet after river propagation time delay correction.

[0117] Finally, all sub-flow processes are time-aligned and superimposed at the watershed outlet to form the improved total flow process, such as... Figure 6 As shown.

[0118] Figure 5The dashed line represents the calculation results of the integrated unit hydrograph method in Guangdong Province, while the solid line represents the model results. It can be seen that under design storm conditions of 5-year, 10-year, 20-year, 50-year, 100-year, and 200-year return periods, the peak flow simulated by the integrated unit hydrograph method is generally higher than the simulation results of the urban storm runoff generation and confluence model, and the larger the return period, the more significant the peak flow deviation. Simultaneously, the flood arrival time is generally delayed by 60–80 minutes, significantly deviating from the actual drainage response process. This deviation stems from the integrated unit hydrograph method's failure to accurately reflect nonlinear processes such as surface water storage, pipeline regulation, and river delay in urbanized watersheds, leading to a disconnect between the peak flow morphology and timing and the actual situation. This demonstrates a significant decrease in the applicability of the integrated unit hydrograph method in highly urbanized areas.

[0119] from Figure 6 The dashed line represents the improved total flow process, and the solid line represents the model results. It can be seen that the peak occurrence time difference is less than 10 minutes, and the overall process line has a good fit, demonstrating strong simulation accuracy and engineering applicability. Although the fitting effect has slightly decreased, the peak occurrence time is still basically consistent with the model, indicating that it still has certain applicability under low-to-medium intensity rainstorms. Comprehensive analysis shows that under high return period rainfall conditions, due to high rainfall intensity and concentrated surface runoff processes, urban drainage systems tend to be at full capacity, and the system response is approximately linear. The improved integrated unit hydrograph method based on urbanization background disclosed in this invention can better characterize urban runoff generation and concentration processes.

[0120] The integrated unit line improvement method applicable to urbanized areas in this embodiment also has the following technical effects:

[0121] 1) This invention addresses the core contradiction in current hydrological simulations of highly urbanized watersheds where "accuracy and efficiency" are difficult to balance. For the first time, it proposes a systematic improved method for the integrated unit hydrograph method. While retaining the advantages of the traditional unit hydrograph method—simple parameters and ease of application—this method effectively incorporates key factors unique to urbanized watersheds, such as drainage networks and water storage effects. It fills the technical gap in the adaptability of the existing integrated unit hydrograph method to urbanized watersheds and provides a new technical approach for flood calculations in urbanized areas with limited or no data.

[0122] 2) The integrated unit hydrograph method, based on the linear time-invariant assumption, is difficult to accurately reflect the nonlinear characteristics of pipeline transportation and drainage capacity limitations in urbanized watersheds. This invention introduces a spatiotemporal reconstruction mechanism based on drainage system layout to establish a method for transforming centralized flow processes into distributed sub-flow processes. Furthermore, it quantifies the actual discharge capacity of drainage outlets by adjusting factors and constructs a storage and discharge response correction algorithm to achieve accurate simulation of pipeline transportation capacity limitations and water storage-release processes, effectively improving the calculation accuracy of flood hydrographs, especially key features such as peak flow and peak time.

[0123] 3) This invention establishes a segmented delay superposition mechanism from the drainage unit to the watershed outlet, simultaneously considering both pipeline and river propagation time delays, thus achieving a systematic simulation of complex confluence paths in urbanized watersheds. This improvement allows the method to generate flow process lines with accuracy comparable to refined models while maintaining the advantages of the integrated unit hydrograph method, such as high computational efficiency and low parameter requirements. This significantly enhances the practicality and reliability of the method in scenarios requiring rapid assessment, such as engineering planning and design, and flood emergency response, providing strong technical support for urban hydrological analysis and flood risk management.

[0124] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the integrated unit line applicable to urbanized areas, characterized in that, Includes the following steps: S1. Based on the basic data of the study area, an urban storm runoff generation and confluence model was constructed to simulate the flow process at the watershed outlet section under design storms with different return periods, serving as the baseline result; S2. Calculate the flow process at the outlet section of the watershed under the same design storm, reconstruct it spatiotemporally, and transform it into a centralized flow process, specifically: The unit hydrograph sequence of the watershed was determined using the integrated unit hydrograph method, based on the watershed area, main stream length, water catchment area characteristic parameters, runoff parameters, lag time values, and average after-loss rate of the study area. The net rainfall sequence of the designed rainstorm period is convolved with the unit hydrograph sequence to obtain the original flow process at the watershed outlet section. Assuming rainfall-runoff is an instantaneous response, the inherent propagation lag of the original flow process is eliminated, and it is reconstructed into a centralized flow process; S3. Based on the layout of the drainage system, the centralized flow process is spatially allocated to form two types of sub-flow processes: drainage outlets and river sections, specifically: Spatial allocation is based on the physical structural characteristics of the drainage system in the study area; wherein, the physical structural characteristics include: the distribution density of drainage outlets, the total length of drainage pipelines, the distribution density of rivers, and the total length of river channels; By quantitatively analyzing the physical structural characteristics of the drainage system, the equivalent weights representing the relative importance of the river confluence path and the drainage outlet confluence path are calculated. Based on the equivalent weights, the centralized flow process is divided into the drainage outlet sub-flow process and the river channel sub-flow process according to the weight ratio of each unit of the drainage system. S4. Based on the actual maximum discharge capacity of the drainage outlet, implement storage and discharge response correction for the sub-flow process of the drainage outlet to form a time-series flow process considering drainage capacity constraints, specifically: At each calculation moment, determine the relationship between the current flow rate of the sub-flow process at the drainage outlet and its actual maximum discharge capacity; Based on the actual release or retention situation, the total amount of water accumulated in the retention unit is updated again, and the calculation proceeds to the next time step, ultimately forming a time-series flow process that considers drainage capacity constraints. S5. Calculate the propagation time delays of the pipelines and rivers from the drainage unit to the watershed outlet, segment the time-series flow process, and obtain the improved total flow process after time alignment and superposition, as follows: The flow process after storage and discharge response correction is regarded as uniformly distributed along the length of the drainage pipeline, and the flow is divided into several segments according to the maximum propagation time and the calculation time step, flowing into the river at different time points; After the flow enters the river, the propagation time along the river to the watershed outlet is determined based on the relative position of the drainage outlet on the river. All delayed sub-flow processes are aligned and superimposed at the watershed outlet section according to time series to obtain the improved total flow process. The flow process, after correction for storage and discharge response, is considered to be uniformly distributed along the length of the drainage pipeline. Based on the maximum propagation time and the calculation time step, the flow is divided into several segments. The calculation formula for the flow into the river at different time points is as follows: ; In the formula, For drainage outlet After the storage and discharge correction, at time The flow rate value; For the drain outlet Sub-flow process After delay processing, The flow rate flowing into the river at any given time; For drainage outlet The number of sub-flow processes segmented within the pipe, through the drain outlet. The ratio of the maximum propagation time to the calculation time step is determined and rounded up. Assign weighting coefficients to traffic.

2. The method for improving the integrated unit line applicable to urbanized areas according to claim 1, characterized in that, S1, based on the basic data of the study area, constructs an urban stormwater runoff generation and confluence model to simulate the flow process at the watershed outlet section under design storms with different return periods. Specifically: The urban stormwater runoff model includes: a one-dimensional pipe network model MIKE Urban, a one-dimensional river channel model MIKE 11, and a two-dimensional surface runoff model MIKE 21; The one-dimensional pipe network model MIKEUrban was constructed using land use data, topographic elevation data, and drainage pipe network data. The design storm was input into the one-dimensional pipe network model MIKE Urban and the one-dimensional river channel model MIKE 11 to obtain the overflow node location and overflow process; The overflow process is input into the two-dimensional surface runoff model MIKE 21 to simulate the surface water depth, inundation range and surface runoff process; By comparing the simulation results of surface water depth, inundation range and surface runoff process with measured data, the parameters of the one-dimensional pipe network model MIKE Urban, the one-dimensional river channel model MIKE 11 and the two-dimensional surface runoff model MIKE 21 were calibrated and verified. The design storms with different return periods are input into the calibrated and verified urban storm runoff generation and confluence model, and the flow process data of the watershed outlet section are output.

3. The method for improving the integrated unit line applicable to urbanized areas according to claim 1, characterized in that, The method for obtaining the actual maximum discharge capacity of the drainage outlet in step S4 is as follows: Several representative drainage outlets in the study area were selected, and the measured maximum flow of the representative drainage outlets under different return periods of design rainstorms was simulated by a calibrated and verified urban storm runoff generation and confluence model. The sum of the measured maximum flow of the representative drainage outlets was obtained. The theoretical maximum total flow rate of representative drainage outlets was calculated based on Manning's formula.

4. The method for improving the integrated unit line applicable to urbanized areas according to claim 1, characterized in that, The process of determining the relationship between the current flow rate of the sub-flow process at each calculation moment and its actual maximum discharge capacity is as follows: If the flow rate of the sub-flow process at the drain outlet exceeds the actual maximum discharge capacity at the current moment, the excess is stored in a virtual storage unit. At this time, the actual outflow of the drain outlet is limited to its actual maximum discharge capacity and updated to the total amount of water in the storage unit. If the flow rate of the sub-flow process at the drainage outlet does not exceed the actual maximum discharge capacity at the current moment, then discharge is carried out at that flow rate and the remaining discharge capacity is calculated; at the same time, the difference between the actual maximum discharge capacity and the current flow rate is calculated; based on the ratio of the current total water volume to the historical maximum total water volume, the theoretically releaseable water volume is calculated; the actual water release volume is the smaller value between the current remaining discharge capacity and the theoretically releaseable water volume. If the accumulated water is released, the flow rate at a certain moment is equal to the flow rate of the atomic flow process at that moment plus the actual amount of accumulated water released.

5. The method for improving the integrated unit line applicable to urbanized areas according to claim 1, characterized in that, S5 calculates the propagation time delay of water flow from each drainage unit to the watershed outlet, specifically as follows: Calculate the average flow velocity inside the drainage outlet and in the river channel, respectively; The average length of the drainage pipe is determined based on the total length of the drainage pipe and the distribution density of the drainage outlets. The maximum propagation time of each drainage outlet is calculated by combining the average flow velocity of the drainage outlets. The average river length is determined based on the total river length and the river distribution density, and the maximum propagation time of each river is calculated by combining the average river flow velocity.

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