A method for determining an urban stormwater inlet inflow hydrograph

Abstract

The application provides a method for determining inflow hydrograph of urban stormwater inlet, which is in line with actual urban runoff conditions and can effectively reduce the error of calculation results. The urban area is divided into multiple sub-regions according to the road network, and the net rainfall is discharged from the stormwater inlet, and the single stormwater inlet in the sub-region is calculated respectively; the urban surface runoff is calculated by using the comprehensive runoff coefficient method, and the runoff coefficient not greater than 1 is used to represent the runoff after the rainfall is intercepted and lost on the ground; for the rainfall in the small urban area, the ground water flow is in the form of slope flow and shallow concentrated flow; the catchment time is the sum of the two, the slope flow with a flow line not greater than 90m is calculated by using the Manning dynamics method to calculate the surface runoff flow time; after the slope flow stops flowing for 90m, the shallow concentrated flow with a water depth greater than 3cm appears at this time, and the stormwater inlet design flow inflow calculation formula is: Q = F * (P - S) / (T + 90) wherein Q is the stormwater inlet inflow, L / min; F is the average catchment area controlled by each stormwater inlet, m 2 .

Description

TECHNICAL FIELD

[0001] The application belongs to the field of urban rainfall inlet flow calculation, and particularly relates to a method for determining an urban rainfall inlet flow hydrograph. BACKGROUND

[0002] Currently, the key research target of watershed hydrology is gradually shifting to urban watersheds, and more and more attention is paid to a series of problems caused by the increasing effect of impervious surface runoff. Under the background of rapid expansion of urban scale, the urban building density is high, the proportion of hardening road surface is large, and the surface building is updated quickly, so the surface rainwater runoff is not only affected by the rainfall intensity and rainfall, but also affected by the complex land use type of the surface.

[0003] The hardening road surface with high density and large proportion and the impervious building are the main factors affecting the urban surface runoff. Compared with the pervious road surface, the traditional impervious road surface has the advantages of low cost, good durability and quick construction, so its application range is wider. The artificial watershed runoff process of the building with high density and the traditional impervious road surface is quite different from the traditional watershed runoff process, so it is difficult to explain by using the traditional calculation method. The slope runoff model simulates the hydrological sub-process from precipitation to runoff to slope runoff, and the current urban surface runoff calculation method mainly includes hydrological method and hydrodynamic method, and many models such as TOP-MODEL, GBHM and SHE model are also developed and established. The urban rainwater runoff research usually divides the region according to the land use classification data and urban design scheme to obtain a runoff model suitable for the sub-region, and can be divided into water surface runoff model, green space pervious layer runoff model, building and road impervious layer runoff model and open land and impervious layer runoff model. In the study of the runoff and runoff process of the impervious area of the building and road, scholars regard the rainwater on the top of the building as ordinary rainfall and count it into the surface rainwater runoff, thereby ignoring the real influence of the building on the rainfall. In fact, many buildings are treated so that the accumulated rainwater directly enters the underground drainage system through the pipeline, the area of the building impervious layer accounts for a high proportion in the central city, the building density is large, and the rainwater runoff is greatly affected by the building and the rainwater inlet. This results in a large error in the calculation result of the urban rainwater inlet flow. Moreover, in order to ensure smooth drainage and not cause related problems, the rainwater inlets are widely distributed in the urban road, and the catchment area is very small. The traditional rainwater inlet flow calculation method has many assumed conditions, the influence of uncertainty is large, and the calculation result cannot well fit the actual situation. SUMMARY

[0004] In view of the above technical problems, the application provides a method for determining an urban rainwater inlet flow hydrograph, which fits the actual urban runoff situation and can effectively reduce the error of the calculation result.

[0005] The specific technical scheme is as follows:

[0006] In the urban area, the terrain is complex, and the reasons for rainfall loss are different. Green land, plants, water surface, etc. can cause large rainfall loss caused by net interception and infiltration; in other impervious surfaces in urban areas such as buildings, roads and other types of impervious layers, the filling loss caused by depression in the depression; surface rainwater evaporation mainly occurs after the end of rainfall, affecting the humidity of the previous period of the next rainfall, so the rainfall loss caused by evaporation can be ignored for a single rainfall.

[0007] The present application considers that in fact, only a small amount of surface flow flows into the pipe network from the inspection well, and the rainfall loss caused by the infiltration of impervious ground is negligible, and most of the rainwater enters the rainwater well through the rainwater inlet located on both sides of the road, and the surface water flow converges to the rainwater inlet slightly lower than the ground on both sides of the road. The present application divides the urban area according to the main road network, and the net rainfall is discharged from the rainwater inlet, and the single rainwater inlet in the sub-region is calculated respectively, thereby reducing the system error caused by the model.

[0008] The single catchment area is very small, in order to avoid the complex problem caused by the multiple types of rainfall loss and the complex surface of the urban area, and to reduce the influence of the runoff difference of part of the rainwater inlet catchment area, the present application adopts the comprehensive runoff coefficient method to calculate the urban surface runoff, and the runoff coefficient is not greater than 1 Indicates the runoff after the rainfall is intercepted and lost on the ground.

[0009]

[0010] In the formula: is the runoff coefficient, dimensionless; R is the runoff of a certain area in a certain period, mm; P is the precipitation of the same area in the same period, mm;

[0011] The outdoor drainage design standard (GB50014-2021) (hereinafter referred to as the standard) stipulates that the runoff coefficient of the ground cover type is as follows:

[0012] Table 1 Runoff coefficient of ground cover type

[0013]

[0014] The comprehensive runoff coefficient calculation formula is as follows:

[0015]

[0016] In the formula: is the comprehensive runoff coefficient; S i is the area of various types of ground cover on the regional terrain; Corresponding runoff coefficient for the corresponding ground type. Where the building impermeable layer of rainfall through the pipeline directly into the sewer network, not into the surface production and concentration calculation, so the application in the comprehensive runoff coefficient calculation considers that the building area does not participate in the weight proportion, according to the actual terrain to correct the comprehensive runoff coefficient.

[0017] The surface rainwater runoff intensity calculation formula is as follows:

[0018]

[0019] In the formula: r is the regional net runoff intensity, mm / min; i is the regional rainfall intensity, mm / min.

[0020] The urban surface is different from the natural basin, the surface runoff and net rain runoff process is quite different, the urban impermeable surface accounts for a high proportion, the runoff coefficient is large, the production and concentration time is short, and the rainwater runoff is obviously affected by the rainwater outlet, and the rainwater runoff is also relatively rapid. For the urban area, the application assumes that the runoff occurs immediately after the rainfall, and the runoff time is ignored, and the rainfall collection time and the water recession time after the rainfall are considered. The standard does not have a specific calculation formula for the ground water collection time and the water recession time, and the recommended value range of the ground water collection time is given, and the water recession time is limited for the waterlogging caused by the waterlogging in the densely populated, economically better and densely populated areas, and the water recession time is limited for the waterlogging in the densely populated, economically better and densely populated areas. The general rainfall has no requirement. In order to solve the problem of uncertain value of the water collection time, the formula is used for calculation.

[0021] For the rainfall of a small urban area, the ground water flow state is mainly slope flow and shallow concentrated flow. The water collection time is the sum of the two, the slope flow with a flow line of less than 90m, the Mannering dynamics method is used to calculate the surface runoff flow time, and the flow time calculation formula is:

[0022]

[0023] In the formula: t1 is the flow time, min; l1 is the water collection distance, m; n is the Mannering coefficient corresponding to the water depth of 3cm and below; S is the ground slope; P2 is the two-year return period 24h rainfall, mm.

[0024] After the slope flow stops for 90m, shallow concentrated flow with water depth greater than 3cm appears at this time, and the flow time t2 calculation formula is:

[0025]

[0026] In the formula: t2 is the flow time, min; l2 is the water collection distance, m; K is the surface runoff coefficient when the shallow concentrated flow is;

[0027] The isochrone method, linear reservoir method and nonlinear reservoir method have good effect in natural basin, but the ground runoff process of rainwater outlet basin is different from the above-mentioned concentration system, and the actual catchment area of a single rainwater outlet is far less than 2km 2 The standard stipulates that the design flow of the rainwater pipe and channel is calculated by the reasoning formula method at this time, so the reasoning formula method with the correction coefficient is used to calculate the design flow of the rainwater outlet of the urban area, the unevenness of rainfall on the small catchment area is small, so it can be considered that the rainfall is uniformly distributed.

[0028] The inflow calculation formula of the design flow of the rainwater outlet is:

[0029]

[0030] In the formula, Q is the inflow of the rainwater outlet, L / min; F is the average catchment area controlled by each rainwater outlet, m 2 If it cannot be determined, it can be selected generally; the rest is the same as above.

[0031] For the determination of the F controlled paving area, the present application considers that a reduction coefficient β should be multiplied on the basis of the control area to represent the actual situation that the rainfall on the roof of the impervious building does not flow into the rainwater outlet, and β is related to the building density.

[0032] The relevant specification does not have specific and in-depth standards for the impervious surface in urban area rainwater runoff, the present application further subdivides the rainfall on the high-density impervious surface of the city, excludes the influence of the rainfall on the roof of the impervious surface, and the calculation results of the urban rainwater runoff and the inflow of the rainwater outlet are more reliable. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is the technical flow chart of the calculation method of the present application;

[0034] Figure 2 It is the digital elevation model diagram of the Wuhou District of the present application;

[0035] Figure 3 It is the terrain slope value of the Wuhou District of the present application;

[0036] Figure 4 It is the land use type of the Wuhou District of the present application;

[0037] Figure 5 It is the rainfall intensity process line (return period 2 years, rainfall duration 120 minutes) of the present application. DETAILED DESCRIPTION

[0038] The specific implementation mode of the present application is illustrated by combining with examples.

[0039] This embodiment takes the Wuhou District of Chengdu City as an example, and the flow is as shown in Figure 1 .

[0040] Chengdu Wuhou District is slightly inclined from northwest to southeast, flat terrain, terrain in the form of butterfly, the area is a subtropical humid monsoon climate, hot summer, more rain, rainstorms. The total land area is 75.36km 2 , Wuhou District is under the jurisdiction of 15 streets.

[0041] The present application calculates the relevant parameters of the urban surface by means of ARC GIS software, introduces the calculation method and process of urban runoff. Wuhou District is located between 103°56'45" ~ 104°05'33" east longitude, 30°34'31" ~ 30°39'49" north latitude, downloads ASTER GDEM 30M resolution digital elevation data in geographic spatial data cloud, uses GIS to load DEM and inlay fusion, the projection method is selected as Mercator projection, the calculated projection coordinate system is WGS_1984_UTM_Zone_48N, after cutting, as shown in Figure 2 , the terrain is calculated as shown in Figure 3 , the average slope of Wuhou District is 3.73%. The building, road and green data are projected to WGS_1984_UTM_Zone_48N, and other land cover utilization data such as water system is ignored, and the regional terrain is shown in Figure 4 . According to the calculation, the total area of building is about 24.4km 2 , accounting for 32.4%, the green area is about 1.91km 2 , accounting for 2.5%.

[0042] Other impervious surface has no specific data, 70% of other surface except building and green is generalized as asphalt and concrete pavement, and the other 30% is generalized as block stone pavement. The area of regional surface is as follows:

[0043] Table 2 Area of surface type of Wuhou District of Chengdu

[0044] Ground type Building Asphalt, concrete pavement Block stone pavement Green land Area (km 2 )]]> 24.4 34.34 14.71 1.91

[0045] The comprehensive runoff coefficient is calculated by formula 2 as follows:

[0046]

[0047] The storm intensity formula of Chengdu central urban area is:

[0048]

[0049] Where: i is the average rainfall intensity of the time period, mm / min; P is the return period, years; t is the rainfall duration, min; the return period is taken as 2 years, the rainfall duration is taken as 120 min, and i is calculated as 0.468 mm / min. The regional average runoff intensity is r = 0.79 x 0.468 = 0.370 mm / min.

[0050] The present rainfall uses the Chicago synthetic rainfall process line method, as shown in Figure 5 , the peak ratio r1 is taken as 0.4, and the instantaneous rainfall intensity table is calculated by substituting the relevant parameters as follows:

[0051] Table 3 Rainfall Instantaneous Intensity Table

[0052]

[0053]

[0054] According to the above table, the actual instantaneous runoff intensity table of the rainfall is as follows:

[0055] Table 4 Rainfall Instantaneous Runoff Intensity Table

[0056]

[0057]

[0058] The number and location of rainwater inlets in the region have no accurate data, and the control paving area is taken as 200 m 2 , and the reduction coefficient β is calculated as follows:

[0059]

[0060] The actual value F is calculated as = 0.67 x 200 = 134 m 2 .

[0061] The average control area of a single rainwater inlet is very small, and the ground surface only has slope flow, so the rainfall catchment time is the flow time of the slope flow. The rainfall duration is changed to 24 h, and the remaining conditions remain the same as the above simulated rainfall. The two-year return period rainfall P2 is 45.0869 mm; the urban rainwater runoff flows on the asphalt and concrete surface, and the Manning coefficient n is taken as 0.015; the ground slope S is 3.73%; the catchment distance is set to 90 m, and t1 is calculated as 3.86 min by formula 4, and the actual value is taken as 4 min.

[0062] The rainwater inlet design flow inflow calculation results are as follows:

[0063] Table 5 Rainwater Inlet Inflow Rainfall Table

[0064]

[0065]

[0066] The above descriptions are merely some embodiments of the present application, but are not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for determining the inflow process line of urban storm drains, characterized in that, The method comprises the following steps: The urban area is divided into multiple sub-areas according to a road network, and the net rainfall is discharged by a rainwater inlet; and the single rainwater inlet in each sub-area is calculated respectively; The urban surface runoff is calculated by using the comprehensive runoff coefficient method, and the runoff coefficient is not greater than 1 The runoff after the rainfall is intercepted and lost on the ground is represented. = R / P (1) wherein: R is the runoff coefficient, dimensionless; R is the runoff of a certain area in a certain period, mm; P is the precipitation of the same area in the same period, mm; The comprehensive runoff coefficient calculation formula is as follows: （2） In the formula: is the comprehensive runoff coefficient; is the area of each type of surface cover on the regional terrain; is the runoff coefficient corresponding to the respective ground type; The surface rainwater runoff intensity calculation formula is as follows: （3） In the formula, r is the area net runoff intensity, mm / min; i is the area rainfall intensity, mm / min; For urban small area rainfall, the ground water flow flow pattern is slope flow and shallow water concentrated flow; the catchment time is the sum of the two, the slope flow with a flow line not greater than 90 m, the Manning dynamics method is used to calculate the surface runoff flow time, and the flow time calculation formula is as follows: （4） In the formula, t1 is the flow time, min; l1 is the catchment distance, m; n is the Manning coefficient corresponding to 3 cm and below water depth; S is the ground slope; P2 is the 24 h rainfall of the two-year return period, mm; After the slope flow flows for 90 m and stops, at this time, the shallow water concentrated flow with a water depth greater than 3 cm appears, and the flow time t2 calculation formula is as follows: （5） In the formula, t2 is the flow time, min; l2 is the catchment distance, m; K is the surface runoff coefficient when the shallow water concentrated flow flows; The rainwater inlet design flow inflow calculation formula is as follows: （6） Where: Q = inlet flow rate of the gutter, L / min; F = average catchment area controlled by each gutter, m2; t = duration of rainfall, min. 2 ; t = duration of rainfall, min. For the determination of the F control paving area, a reduction coefficient β is multiplied to represent the actual situation that the rainfall on the non-porous building roof does not flow into the rainwater inlet, and the β is related to the building density.

Images