Composite rainwater garden meeting urban runoff multi-target monitoring and experimental method

Abstract

The invention particularly discloses a composite rainwater garden meeting urban runoff multi-target monitoring and an experimental method.The composite rainwater garden comprises an infiltration type rainwater garden and a drainage type rainwater garden, and the infiltration type rainwater garden is communicated with a rainwater collecting route through an infiltration type rainwater garden inflow channel; the drainage type rainwater garden is communicated with the rainwater collecting route through the drainage type rainwater garden inflow channel, the infiltration type rainwater garden is communicated with the reservoir through the infiltration type rainwater garden overflow channel, and the drainage type rainwater garden is communicated with the reservoir through the drainage type rainwater garden overflow channel. Through the arrangement of two different structures of rainwater gardens and the research design of the hydrological process, the two different structures of rainwater gardens are constructed adjacently, and meanwhile, the same roof runoff is utilized, so that the consistency of factors such as soil conditions and rainfall properties can be effectively ensured, and the interference of uncontrollable factors on research results is weakened; and it is ensured that research results are more targeted and more comprehensive.

Description

Technical Field

[0001] The present invention relates to the technical field of application of low-impact development measures for sponge cities, and specifically to a composite rainwater garden and an experimental method for satisfying multi-objective monitoring of urban runoff. Background Art

[0002] The construction of sponge cities must first strengthen the regional control of rainwater and effectively reduce the source. If the rainwater in each area can be effectively digested on the spot, the overall rainwater problem in the city will naturally be solved.

[0003] At present, how to achieve effective on-site digestion of rainwater in various areas is still in the exploratory stage, and there is no mature means. The rainwater garden of the present invention, as one of the typical measures under the concept of sponge city, has multiple functions such as intercepting rainwater, reducing surface runoff, replenishing groundwater and controlling urban non-point source pollution. For this purpose, a composite rainwater garden and experimental method that meet the multi-target monitoring of urban runoff are provided. Summary of the invention

[0004] The purpose of the present invention is to address the defects of the prior art and provide a composite rain garden and experimental method that can meet the multi-objective monitoring of urban runoff, so as to solve the problems raised by the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a composite rain garden that meets the requirements of multi-target monitoring of urban runoff, including an infiltration type rain garden and a drainage type rain garden, wherein the infiltration type rain garden is connected to a rainwater collection route through an infiltration type rain garden inflow channel, the drainage type rain garden is connected to a rainwater collection route through a drainage type rain garden inflow channel, the infiltration type rain garden is connected to a reservoir through an infiltration type rain garden overflow channel, the drainage type rain garden is connected to a reservoir through a drainage type rain garden overflow channel, an automatic water suction pump is installed at the bottom of the reservoir, and the automatic water suction pump is connected to the outside through a water pipe;

[0006] The infiltration type rain garden inflow channel is provided with a first inflow channel grid filter trough and a first rain garden inflow weir plate, and the drainage type rain garden inflow channel is provided with a second inflow channel grid filter trough and a second rain garden inflow weir plate, the first rain garden inflow weir plate and the second rain garden inflow weir plate are arranged away from the direction of the rainwater collection route, and the first inflow channel grid filter trough and the second inflow channel grid filter trough are arranged close to the direction of the rainwater collection route;

[0007] The infiltration type rain garden overflow channel is equipped with a first rain garden overflow weir plate and a first overflow road grid filter tank; the drainage type rain garden overflow channel is equipped with a second rain garden overflow weir plate and a second overflow road grid filter tank, the first rain garden overflow weir plate and the second rain garden overflow weir plate are arranged close to the water storage tank, and the first overflow road grid filter tank and the second overflow road grid filter tank are arranged away from the water storage tank;

[0008] A perforated pipe drainage channel is also provided on one side of the overflow channel of the drainage type rain garden, a perforated pipe overflow weir is installed at the connection between the perforated pipe drainage channel and the water storage tank, and a perforated drainage pipe is installed inside the perforated pipe drainage channel;

[0009] The infiltration type rain garden is equipped with a first water level monitor and a first trime pipe; the drainage type rain garden is equipped with a second water level monitor and a second trime pipe;

[0010] A groundwater level monitoring well is provided on one side of the infiltration rain garden.

[0011] The infiltration type rain garden is composed of an infiltration type rain garden planting soil layer and an infiltration type rain garden covering soil layer;

[0012] The drainage type rain garden is provided with a drainage type rain garden planting soil layer, a drainage type rain garden biological filtration layer, a drainage type rain garden gravel layer, and a drainage type rain garden fine sand medium layer in sequence from the surface downward;

[0013] The interior of the drainage rain garden is paved with a composite impermeable geomembrane, and the edge is flush with the water storage layer of the drainage rain garden and hidden inside the slope. The bottom of the fine sand medium layer of the drainage rain garden is provided with a perforated drainage pipe wrapped with a permeable geomembrane. The perforated drainage pipe is buried in the middle position of the bottom of the drainage rain garden along the long axis direction of the drainage rain garden.

[0014] As a preferred technical solution of the present invention, the rainwater collection route is arranged under the eaves of the house and has the same length as the eaves, so as to collect rainwater from the eaves.

[0015] As a preferred technical solution of the present invention, an experimental rainwater sampling platform is provided at one end of the water storage tank;

[0016] As a preferred technical solution of the present invention, the outlet of the perforated drainage pipe of the drainage type rain garden overflow channel is arranged in the drainage trough of the perforated pipe drainage channel, and the outlet extends horizontally into the drainage trough by 18-20 cm, and the drainage trough is connected to the water storage tank.

[0017] As a preferred technical solution of the present invention, a drainage pipe is laid horizontally at the bottom of the drainage rain garden, and a number of 1 cm long and 3 mm wide holes are opened around the drainage pipe. The outside of the drainage pipe is wrapped with a permeable geomembrane to prevent soil particles from clogging the pipe holes.

[0018] As a preferred technical solution of the present invention, the rainwater collection route is connected to the roof rainwater pipe of the house. The rainwater collection route is located below the ground, and sealed waterproof walls are laid radially around to form a water flow channel, and a slope is set for the circulation of rainwater. The infiltration type rainwater garden overflow channel and the drainage type rainwater garden overflow channel are fixedly installed with a first paperless water level flow recorder; the infiltration type rainwater garden inflow channel and the drainage type rainwater garden inflow channel are fixedly installed with a second paperless water level flow recorder to record the flow process, a second water level gauge is installed on one side of the infiltration type rainwater garden inflow channel and the drainage type rainwater garden inflow channel, and a first water level gauge is installed on one side of the infiltration type rainwater garden overflow channel and the drainage type rainwater garden overflow channel.

[0019] As a preferred technical solution of the present invention, the first rain garden inflow weir, the second rain garden inflow weir, the first rain garden overflow weir, the second rain garden overflow weir and the perforated pipe overflow weir are all provided with inverted triangular overflow ports in the middle of the tops. The bottom angle of the inverted triangular overflow ports of the first rain garden overflow weir, the second rain garden overflow weir and the perforated pipe overflow weir is 30 degrees, and the bottom angle of the inverted triangular overflow ports of the first rain garden inflow weir and the second rain garden inflow weir is 60 degrees.

[0020] A construction method for a composite rain garden, the specific steps are as follows:

[0021] Step 1: Construction method of drainage rain garden;

[0022] Step 1.1: Site selection: Select a solid dirt ground near the house and the rainwater downpipe;

[0023] Step 1.2: Drainage rain garden foundation pit: dig an elliptical drainage rain garden pit with a depth of 1-1.2 meters 2-3 meters away from the roof in the vertical direction of the ground. Form a vertical pit wall around the drainage rain garden pit, and dig a water storage pit next to the drainage rain garden pit;

[0024] Step 1.3: Dig inlet and outlet channels: Dig an inlet channel on the side of the drainage rain garden pit close to the eaves, and dig an outlet channel on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30 cm higher than the surface of the drainage rain garden planting soil layer;

[0025] Step 1.4: Lay out a drainage rain garden: Lay a 20cm thick fine sand medium layer on the geomembrane at the bottom of the pit, and lay a 110mm diameter perforated drainage pipe along the long axis of the ellipse. The outer layer of the perforated drainage pipe is wrapped with a permeable geomembrane of corresponding strength to prevent soil particles from blocking the pipe holes. The length of the overflow channel perforated drainage pipe is greater than the long axis of the ellipse, and a 20cm excess is reserved on the water outlet of the elliptical pit of the rain garden to discharge water into the drainage channel and enter the reservoir;

[0026] Step 1.5: Drainage channel: dig a 0.4-meter-wide outlet channel at the outlet of the perforated drainage pipe at the bottom of the drainage rain garden with the same depth as the bottom of the rain garden pit. Build a concrete isolation wall to separate the outlet channel from the inside of the garden, leaving only the perforated drainage pipe position connected to the outside. Place an outlet triangular weir plate 1 meter away from the outlet channel for flow monitoring during rainfall. The weir angle should be 5 cm lower than the perforated drainage pipe outlet to prevent rainwater backflow due to untimely drainage. The outlet channel is located 1.2 meters below the ground, so an experimental rainwater sampling platform is built at the tail of the outlet channel to facilitate sampling during the experiment and water storage tank maintenance.

[0027] Step 1.6: Setting of confluence channel: Dig a 40 cm wide concrete confluence channel along the eaves to ensure that the confluence channel is flat and the longitudinal slope of the road is less than 1%. Set up a water retaining slope 10 cm above the ground around the confluence channel to prevent rainwater from leaking sideways. Rainwater flows into the rain garden along the confluence channel.

[0028] Step 1.7: Set up the inflow weir plate and overflow weir plate: The layout method is the same as that of the drainage channel. The difference is that in order to adapt to different rainfall intensities, the inflow weir plate is set as a removable movable weir plate. When the rainfall intensity is large, the weir angle can be flexibly changed to adjust the inflow flow to prevent overflowing;

[0029] Step 2: Construction method of infiltration rain garden;

[0030] Step 2.1: Site selection: Same drainage type rain garden, arranged in parallel with the drainage type rain garden;

[0031] Step 2.2: Dig inlet and outlet channels: Dig a 40cm wide inlet channel on the side of the infiltration rain garden pit close to the eaves, and dig an outlet channel of the same width on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30cm higher than the surface of the planting soil layer of the infiltration rain garden;

[0032] Step 2.3: Dig a pit of the same area as the drainage rain garden and 1 meter deep. After digging, fill it with 30 cm of planting soil and 50 cm of covering soil. The remaining 20 cm is the reserved water storage depth.

[0033] Step 2.4: Set up the inflow weir and overflow weir: The layout method is the same as that of the drainage rain garden;

[0034] Step 2.5: Lay a 3-meter Trime pipe inside the garden, with the pipe opening 0.5 meters above the ground. The Trime pipe is used to monitor soil moisture before and after rain;

[0035] Step 2.6: Install a groundwater level monitor inside the garden, with the pipe mouth 0.5 meters above the ground. The groundwater level monitor is used to monitor the soil moisture content before and after rain.

[0036] A test method for a composite rain garden includes the following steps:

[0037] Step a: Determine the detailed inflow and outflow process of the infiltration type rain garden and the drainage type rain garden: Place paperless water level flow recorders at the inflow channel and the overflow channel respectively, and calculate the absolute water pressure recorded by the paperless water level flow recorder and the atmospheric pressure to obtain the change of the water level height h of the triangular weir at different outflows. The data collection frequency is set to 1min and converted into instantaneous flow to accurately measure the inflow and outflow of the rain garden; the interception and reduction effects and differences of the two types of rain gardens on rainwater can be qualitatively analyzed;

[0038] Triangular weir flow calculation formula:

[0039]

[0040] Where: Q is the wastewater flow rate, unit: m 3 / s; h is the geometric head of the weir, m, which is automatically recorded by a paperless water level flow recorder;

[0041] θ is the weir angle, in degrees, where the inlet weir is 30-60 degrees, the outlet weir is 45 degrees, and the drainage weir is 30 degrees;

[0042] μ is the flow coefficient, μ=0.6; g is the acceleration of gravity, g is 9.808m / s;

[0043] Step b: Laying out the trime pipes of the drainage and infiltration rain gardens. Using detectors to automatically detect the changes in soil moisture content at different depths in the pipes before and after rain, quantitatively analyzing the physical process of the two types of rain gardens in terms of rainwater infiltration and retention rules during rainfall events and the effects on groundwater recharge, thus providing constructive suggestions for actual projects.

[0044] Step c: Water quality monitoring: Arrange enough experimental personnel to collect water samples from the inflow, outflow and drainage outlets of the two rain gardens at the early, middle and late stages of rainfall, and monitor the pollutant indicators in the water samples. Compare and analyze the differences in the degradation rules of pollutants in different rain gardens during the same rainfall event, so as to explore the advantages and disadvantages and differences of rain gardens in terms of rainwater storage and flood control under single and combined situations, so as to study a more complete construction plan;

[0045] Step d: Test and record the infiltration performance of drainage rain gardens and infiltration rain gardens:

[0046] In order to avoid the influence of soil infiltration variability, the overall infiltration characteristics of the rain garden will be obtained by the water balance method. When the surface of the rain garden is flooded, evapotranspiration during rainfall can be ignored. The water balance items in the rain garden are inflow, outflow, infiltration and change of water depth in the garden. The inflow and outflow are monitored by triangular weirs, and the change of water depth in the rain garden is obtained by reading the water gauge installed in the garden. Therefore, the total inflow and outflow and the change of water depth in the rain garden within a certain period of time are monitored to obtain the infiltration rate of the rain garden. The soil infiltration rate (K) is:

[0047]

[0048] W in is the total inflow during the period, in m 3 ; ΔH is the change in water depth in the garden during the period, in m; A is the area of ​​the rain garden, in m 2 ; W out The total outflow volume during the period, in m 3 ; According to the actual rainfall situation, the infiltration rate is measured in 2-3 groups as much as possible during each rainfall process, with the time interval Δt of each group controlled to be 2 minutes, and the total measurement time of each group is 30 minutes; by monitoring the soil infiltration capacity and particle composition changes in the rain garden, the sustainability of the infiltration capacity and operation effect of the rain garden during long-term operation is studied;

[0049] Step e: Comparison: By monitoring the soil moisture content at the infiltration point of the rain garden and the changes in the surrounding groundwater level, the impact of the concentrated infiltration of the rain garden on the groundwater can be obtained and reasonable protection measures can be given; by monitoring the water samples of the two rain gardens during rainfall and testing the groundwater quality before and after rainfall, the physical relationship between the changes in the concentration of different pollutants and the concentrated infiltration recharge can be established, and the changing laws of pollutant removal rates in different rain gardens can be studied.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention proposes a design method for a comparative rain garden based on roof runoff. Through the setting of two rain gardens with different structures and the research and design of hydrological processes, with rainwater control and runoff pollution reduction as the main research aspects, it can provide a reference for the effectiveness of the combined utilization of single LID facilities in my country's sponge cities. Building two rain gardens with different structures adjacent to each other and using the same roof runoff can effectively ensure that factors such as soil conditions and rainfall properties remain consistent, thereby reducing the interference of uncontrollable factors on the research results and ensuring that the research results are more targeted and comprehensive.

[0052] Both the infiltration type rain garden and the drainage type rain garden adopt an elliptical structure, with the long axis being the direction of rainwater inflow, which can not only increase the hydraulic retention time, but also meet the landscape design requirements. Deepening the inflow channel by 20cm at the 20cm inlet where the roof rainwater is received can prevent the speed and flow of the rain garden from converging during heavy rain events, relieve the inflow pressure of the triangular weir plate, and improve the soil infiltration efficiency. The inflow port of the drainage type rain garden can simultaneously receive runoff from the roof and the road surface, so as to study the removal capacity of the rain garden for different pollutants and the main sources of pollutants from different aspects. The design advantage of the present invention is that it can solve the problem of singularity when conducting experiments in the rain garden. Through the combined design of the experimental device, the characteristics of the rain garden under different situations and its treatment effect on hydrology and water quality can be monitored simultaneously, in order to provide urban landscape planners with a more comprehensive design reference and evidence.

[0053] As my country strengthens its efforts in sponge city construction and attaches importance to urban stormwater management, single LID measures and their combined model tests are becoming more frequent, and the probability and demand for adopting different LID measures are gradually increasing. This invention will use long-term hydrological monitoring to intuitively illustrate the suitability and effectiveness of rain gardens from different aspects and construction areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a plan layout diagram of the present invention;

[0055] Figure 2 This is a structural diagram of the infiltration type rain garden of the present invention;

[0056] Figure 3 This is a structural diagram of a drainage type rain garden of the present invention;

[0057] Figure 4 This is a layout diagram of the inflow channel of the infiltration type rain garden of the present invention;

[0058] Figure 5 It is a layout diagram of the inflow channel of the drainage type rain garden of the present invention;

[0059] Figure 6 It is the layout diagram of the overflow channel of the infiltration type rain garden of the present invention;

[0060] Figure 7 It is a layout diagram of the overflow channel of the drainage type rain garden of the present invention;

[0061] Figure 8 It is a layout diagram of the overflow channel of the perforated drain pipe of the present invention;

[0062] Fig. 9 It is a cross-sectional view of a water reservoir of the present invention.

[0063] List of reference numerals: 1-roof; 2-rainwater collection route; 3-infiltration type rain garden inflow channel; 4-drainage type rain garden inflow channel; 5-first inflow grid filter trough; 6-second inflow grid filter trough; 7-first rain garden inflow weir; 8-second rain garden inflow weir; 9-infiltration type rain garden; 10-drainage type rain garden; 11-first water level monitor; 12-second water level monitor; 13-first trime pipe; 14-second trime pipe; 15-infiltration type rain garden overflow channel; 16-drainage type rain garden overflow channel; 17-first rain garden overflow weir; 18-second rain garden overflow weir; 19-first overflow grid filter trough; 20-second overflow grid filter Trough; 21-perforated pipe drainage channel; 22-perforated pipe overflow weir plate; 23-reservoir; 24-artificial red brick road; 25-groundwater level monitoring well; 26-experimental rainwater sampling terrace; 27-infiltration type rain garden planting soil layer; 28-infiltration type rain garden covering soil layer; 29-drainage type rain garden planting soil layer; 30-drainage type rain garden biological filtration layer; 31-drainage rain garden gravel layer; 32-drainage type rain garden fine sand medium layer; 33-composite impermeable geomembrane; 34 permeable geomembrane; 35-first paperless water level flow recorder; 36-second paperless water level flow recorder; 37-first water level gauge; 38-second water level gauge; 39-perforated drainage pipe; 40-automatic water suction pump. DETAILED DESCRIPTION

[0064] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0065] Example: See Figure 1-7The present invention provides a technical solution: a composite rain garden that meets the multi-target monitoring of urban runoff, including an infiltration type rain garden 9 and a drainage type rain garden 10, the infiltration type rain garden 9 and the drainage type rain garden 10 are both arranged on one side of a house 1, the infiltration type rain garden 9 is connected to a rainwater collection route 2 through an infiltration type rain garden inflow channel 3, the drainage type rain garden 10 is connected to a rainwater collection route 2 through a drainage type rain garden inflow channel 4, the infiltration type rain garden 9 is connected to a reservoir 23 through an infiltration type rain garden overflow channel 15, the drainage type rain garden 10 is connected to a reservoir 23 through a drainage type rain garden overflow channel 16, an automatic water suction pump 40 is installed at the bottom of the reservoir 23, and the automatic water suction pump 40 is connected to the outside through a water pipe;

[0066] The infiltration type rain garden inflow channel 3 is provided with a first inflow channel grid filter trough 5 and a first rain garden inflow weir plate 7, and the drainage type rain garden inflow channel 4 is provided with a second inflow channel grid filter trough 6 and a second rain garden inflow weir plate 8. The first rain garden inflow weir plate 7 and the second rain garden inflow weir plate 8 are arranged away from the direction of the rainwater collection route 2, and the first inflow channel grid filter trough 5 and the second inflow channel grid filter trough 6 are arranged close to the direction of the rainwater collection route 2;

[0067] The infiltration type rain garden overflow channel 15 is equipped with a first rain garden overflow weir plate 17 and a first overflow road grid filter trough 19; the drainage type rain garden overflow channel 16 is equipped with a second rain garden overflow weir plate 18 and a second overflow road grid filter trough 20, the first rain garden overflow weir plate 17 and the second rain garden overflow weir plate 18 are arranged close to the direction of the water storage tank 23, and the first overflow road grid filter trough 19 and the second overflow road grid filter trough 20 are arranged away from the water storage tank 23;

[0068] A perforated pipe drainage channel 21 is also provided on one side of the drainage type rain garden overflow channel 16. A perforated pipe overflow weir plate 22 is installed at the connection between the perforated pipe drainage channel 21 and the water storage tank 23. A perforated drainage pipe 39 is installed inside the perforated pipe drainage channel 21.

[0069] The infiltration type rain garden 9 is equipped with a first water level monitor 11 and a first trime pipe 13; the drainage type rain garden 10 is equipped with a second water level monitor 12 and a second trime pipe 14;

[0070] A groundwater level monitoring well 25 is provided on one side of the infiltration rain garden 9.

[0071] The infiltration type rain garden 9 is composed of an infiltration type rain garden planting soil layer 27 and an infiltration type rain garden covering soil layer 28;

[0072] The drainage type rain garden 10 is provided with a drainage type rain garden planting soil layer 29, a drainage type rain garden biological filtration layer 30, a drainage type rain garden gravel layer 31, and a drainage type rain garden fine sand medium layer 32 in sequence from the ground surface downward;

[0073] A composite impermeable geomembrane 33 is laid inside the drainage rain garden 10, and its edge is flush with the aquifer of the drainage rain garden 10 and hidden inside the slope. A perforated drainage pipe 39 wrapped with a permeable geomembrane 34 is provided at the bottom of the fine sand medium layer 32 of the drainage rain garden. The perforated drainage pipe 39 is buried in the middle position of the bottom of the drainage rain garden 10 along the long axis direction of the drainage rain garden 10.

[0074] The rainwater collection route 2 is arranged under the eaves of the house 1 and has the same length as the eaves, and is used to collect rainwater from the eaves.

[0075] An experimental rainwater sampling platform 26 is provided at one end of the water storage tank 23;

[0076] The outlet of the perforated drain pipe 39 of the drainage type rain garden overflow channel 16 is arranged in the drainage groove of the perforated pipe drainage channel 21 , and the outlet extends horizontally into the drainage groove by 18-20 cm, and the drainage groove is connected to the water storage tank 23 .

[0077] A perforated drainage pipe 39 is horizontally laid at the bottom of the drainage rain garden 10, and a number of 1 cm long and 3 mm wide pipe holes are opened around the perforated drainage pipe 39. The outside of the perforated drainage pipe 39 is wrapped with a permeable geomembrane 34 to prevent soil particles from clogging the pipe holes. Rainwater from the drainage rain garden enters the corresponding drainage trough through the perforated drainage pipe. When there is enough water in the drainage trough, it flows into the reservoir from the triangular weir corner of the drainage trough.

[0078] The rainwater collection route 2 is connected to the roof rainwater pipe of the house 1. The rainwater collection route 2 is located below the ground. A sealed waterproof wall is laid radially around it to form a water flow channel, and a slope is set for the circulation of rainwater. The infiltration type rainwater garden overflow channel 15 and the drainage type rainwater garden overflow channel 16 are fixedly installed with a first paperless water level flow recorder 35; the infiltration type rainwater garden inflow channel 3 and the drainage type rainwater garden inflow channel 4 are fixedly installed with a second paperless water level flow recorder 36 to record the flow process. A second water level gauge 38 is installed on one side of the infiltration type rainwater garden inflow channel 3 and the drainage type rainwater garden inflow channel 4, and a first water level gauge 37 is installed on one side of the infiltration type rainwater garden overflow channel 15 and the drainage type rainwater garden overflow channel 16.

[0079] The first rain garden inflow weir 7, the second rain garden inflow weir 8, the first rain garden overflow weir 17, the second rain garden overflow weir 18 and the perforated pipe overflow weir 22 are all provided with inverted triangle overflow ports in the middle of the top. The bottom angle of the inverted triangle overflow ports of the first rain garden overflow weir 17, the second rain garden overflow weir 18 and the perforated pipe overflow weir 22 is 30 degrees, and the bottom angle of the inverted triangle overflow ports of the first rain garden inflow weir 7 and the second rain garden inflow weir 8 is 60 degrees.

[0080] A construction method for a composite rain garden, the specific steps are as follows:

[0081] Step 1: Construction method of drainage rain garden 10;

[0082] Step 1.1: Site selection: Select a solid dirt ground near the house and the rainwater downpipe;

[0083] Step 1.2: Drainage rain garden foundation pit: dig an elliptical drainage rain garden pit with a depth of 1-1.2 meters 2-3 meters away from the roof in the vertical direction of the ground. Form a vertical pit wall around the drainage rain garden pit, and dig a water storage pit next to the drainage rain garden pit;

[0084] Step 1.3: Dig inlet and outlet channels: Dig an inlet channel on the side of the drainage rain garden pit close to the eaves, and dig an outlet channel on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30 cm higher than the surface of the drainage rain garden planting soil layer;

[0085] Step 1.4: Lay out a drainage rain garden: Lay a 20cm thick fine sand medium layer on the geomembrane at the bottom of the pit, and lay a 110mm diameter perforated drainage pipe along the long axis of the ellipse. The outer layer of the perforated drainage pipe is wrapped with a permeable geomembrane of corresponding strength to prevent soil particles from blocking the pipe holes. The length of the overflow channel perforated drainage pipe is greater than the long axis of the ellipse, and a 20cm excess is reserved on the water outlet of the elliptical pit of the rain garden to discharge water into the drainage channel and enter the reservoir;

[0086] Step 1.5: Drainage channel: dig a 0.4-meter-wide outlet channel at the outlet of the perforated drainage pipe at the bottom of the drainage rain garden with the same depth as the bottom of the rain garden pit. Build a concrete isolation wall to separate the outlet channel from the inside of the garden, leaving only the perforated drainage pipe position connected to the outside. Place an outlet triangular weir plate 1 meter away from the outlet channel for flow monitoring during rainfall. The weir angle should be 5 cm lower than the perforated drainage pipe outlet to prevent rainwater backflow due to untimely drainage. The outlet channel is located 1.2 meters below the ground, so an experimental rainwater sampling platform is built at the tail of the outlet channel to facilitate sampling during the experiment and water storage tank maintenance.

[0087] Step 1.6: Setting of confluence channel: Dig a 40 cm wide concrete confluence channel along the eaves to ensure that the confluence channel is flat and the longitudinal slope of the road is less than 1%. Set up a water retaining slope 10 cm above the ground around the confluence channel to prevent rainwater from leaking sideways. Rainwater flows into the rain garden along the confluence channel.

[0088] Step 1.7: Set up the inflow weir plate and overflow weir plate: The layout method is the same as that of the drainage channel. The difference is that in order to adapt to different rainfall intensities, the inflow weir plate is set as a removable movable weir plate. When the rainfall intensity is large, the weir angle can be flexibly changed to adjust the inflow flow to prevent overflowing;

[0089] Step 2: Construction method of infiltration rain garden;

[0090] Step 2.1: Site selection: Same drainage type rain garden, arranged in parallel with the drainage type rain garden;

[0091] Step 2.2: Dig inlet and outlet channels: Dig a 40cm wide inlet channel on the side of the infiltration rain garden pit close to the eaves, and dig an outlet channel of the same width on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30cm higher than the surface of the planting soil layer of the infiltration rain garden;

[0092] Step 2.3: Dig a pit of the same area as the drainage rain garden and 1 meter deep. After digging, fill it with 30 cm of planting soil and 50 cm of covering soil. The remaining 20 cm is the reserved water storage depth.

[0093] Step 2.4: Set up the inflow weir and overflow weir: The layout method is the same as that of the drainage rain garden;

[0094] Step 2.5: Lay a 3-meter Trime pipe inside the garden, with the pipe opening 0.5 meters above the ground. The Trime pipe is used to monitor soil moisture before and after rain;

[0095] Step 2.6: Install a groundwater level monitor inside the garden, with the pipe mouth 0.5 meters above the ground. The groundwater level monitor is used to monitor the soil moisture content before and after rain.

[0096] A test method for a composite rain garden includes the following steps:

[0097] Step a: Determine the detailed inflow and outflow process of the infiltration type rain garden 9 and the drainage type rain garden 10: Place paperless water level flow recorders at the inflow channel and the overflow channel respectively, and obtain the change of the water level height h of different outflows at the triangular weir by calculating the absolute water pressure recorded by the paperless water level flow recorder and the atmospheric pressure. The data collection frequency is set to 1min and converted into instantaneous flow to accurately measure the inflow and outflow of the rain garden; the interception and reduction effects and differences of the two rain gardens on rainwater can be qualitatively analyzed;

[0098] Triangular weir flow calculation formula:

[0099]

[0100] Where: Q is the wastewater flow rate, unit: m 3 / s; h is the geometric head of the weir, m, which is automatically recorded by a paperless water level flow recorder;

[0101] θ is the weir angle, in degrees, where the inlet weir is 30-60 degrees, the outlet weir is 45 degrees, and the drainage weir is 30 degrees;

[0102] μ is the flow coefficient, μ=0.6; g is the acceleration of gravity, g is 9.808m / s;

[0103] Step b: Laying out the trime pipes of the drainage and infiltration rain gardens. Using detectors to automatically detect the changes in soil moisture content at different depths in the pipes before and after rain, quantitatively analyzing the physical process of the two types of rain gardens in terms of rainwater infiltration and retention rules during rainfall events and the effects on groundwater recharge, thus providing constructive suggestions for actual projects.

[0104] Step c: Water quality monitoring: Arrange enough experimental personnel to collect water samples from the inflow, outflow and drainage outlets of the two rain gardens at the early, middle and late stages of rainfall, and monitor the pollutant indicators in the water samples. Compare and analyze the differences in the degradation rules of pollutants in different rain gardens during the same rainfall event, so as to explore the advantages and disadvantages and differences of rain gardens in terms of rainwater storage and flood control under single and combined situations, so as to study a more complete construction plan;

[0105] Step d: Detect and record the infiltration performance of the drainage rain garden 10 and the infiltration rain garden 9:

[0106] In order to avoid the influence of soil infiltration variability, the overall infiltration characteristics of the rain garden will be obtained by the water balance method. When the surface of the rain garden is flooded, evapotranspiration during rainfall can be ignored. The water balance items in the rain garden are inflow, outflow, infiltration and change of water depth in the garden. The inflow and outflow are monitored by triangular weirs, and the change of water depth in the rain garden is obtained by reading the water gauge installed in the garden. Therefore, the total inflow and outflow and the change of water depth in the rain garden within a certain period of time are monitored to obtain the infiltration rate of the rain garden. The soil infiltration rate (K) is:

[0107]

[0108] W in is the total inflow during the period, in m 3 ; ΔH is the change in water depth in the garden during the period, in m; A is the area of ​​the rain garden, in m2 ; W out The total outflow volume during the period, in m 3 ; According to the actual rainfall situation, the infiltration rate is measured in 2-3 groups as much as possible during each rainfall process, with the time interval Δt of each group controlled to be 2 minutes, and the total measurement time of each group is 30 minutes; by monitoring the soil infiltration capacity and particle composition changes in the rain garden, the sustainability of the infiltration capacity and operation effect of the rain garden during long-term operation is studied;

[0109] Step e: Comparison: By monitoring the soil moisture content at the infiltration point of the rain garden and the changes in the surrounding groundwater level, the impact of the concentrated infiltration of the rain garden on the groundwater can be obtained and reasonable protection measures can be given; by monitoring the water samples of the two rain gardens during rainfall and testing the groundwater quality before and after rainfall, the physical relationship between the changes in the concentration of different pollutants and the concentrated infiltration recharge can be established, and the changing laws of pollutant removal rates in different rain gardens can be studied, such as nitrogen in particulate and dissolved states.

[0110] Working principle: A composite rain garden, this drainage rain garden, includes adjacent drainage rain gardens and infiltration rain gardens. Both drainage rain gardens and infiltration rain gardens are equipped with rainwater collection routes and overflow channels. The overflow channels are connected to the same reservoir. The rainwater collection routes are located under the eaves of the same specifications and have the same length to ensure that the two rainwater collection routes collect the same amount of rainwater. Groundwater level observation wells are set next to the drainage rain garden and the infiltration rain garden.

[0111] In order to collect and utilize the water discharged from the drainage rain garden 10, a composite impermeable geomembrane 33 of a certain strength is used at its bottom and outside, and some mixed filter materials with good permeability and containing a certain amount of organic matter are selected and filled according to different local soil conditions, and perforated drainage pipes 39 are arranged at corresponding positions. The outer layer of the perforated drainage pipe is wrapped with a permeable geomembrane 34 of corresponding strength to prevent soil particles from clogging the pipe holes;

[0112] In order to improve the regulating and storage function of the rain garden, a drainage type rain garden fine sand medium layer 32 of a certain thickness can be added at the bottom of the perforated pipe, and a drainage type rain garden biological filter layer 30 is set on the upper part of the drainage rain garden gravel layer 31. The drainage type rain garden biological filter layer 30 is composed of 30cm sawdust, aggregates, etc. The backfill thickness of the drainage type rain garden planting soil layer 29 is 30-50cm, and a 20cm water storage layer is reserved.

[0113] The infiltration type rain garden 9 is composed of an infiltration type rain garden planting soil layer 27 and an infiltration type rain garden covering soil layer 28, which can pre-treat the runoff in the catchment area with serious sewage and remove large particle pollutants. The roof runoff enters the front inlet channel of the rain garden through a confluence channel with a longitudinal slope of 1% to 2%, and enters the interior of the rain garden after the flow velocity is slowed down by a triangular weir plate. The elliptical structure of the rain garden is easier to meet the design requirements, prolong the hydraulic retention time, and comply with the landscape design requirements.

[0114] Rainwater collection route 2 receives a dedicated flow channel for roof rainfall, and the longitudinal slope of the flow channel is 1%. In order to facilitate comparative test research and ensure that the rainfall conditions are the same, the present invention divides the roof runoff into two parts. The runoff of rainwater collection route 2 flows into the infiltration type rain garden and the drainage type rain garden respectively.

[0115] The groundwater level monitoring well 25 is used for long-term monitoring of the impact of rain garden construction on groundwater recharge in the area. Groundwater observation wells with different buried depths are set up. In order to ensure the reliability of subsequent experiments, it is recommended that the groundwater level observation system be 2 to 3 meters away from the rain garden.

[0116] An inflow weir is provided at one end of rainwater collection route 2 near the corresponding drainage rainwater garden and infiltration rainwater garden. An inverted triangle inlet is provided on the top of the inflow weir. When the water level in the rainwater collection route reaches the height of the inflow weir, the water flows into the corresponding drainage rainwater garden and infiltration rainwater garden from the inverted triangle inlet on the inflow weir.

[0117] An outflow channel is arranged downstream of the outlet end of the overflow channel. The overflow channel extends horizontally into the outflow channel. The outflow channel is connected to the water storage tank. An outflow weir is arranged at the downstream end of the outflow channel. An inverted triangle overflow port is provided on the top of the outflow weir plate. Water in the drainage type rain garden and the infiltration type rain garden enters the outflow channel from the overflow channel and is blocked by the outflow weir plate until the water level exceeds the inverted triangle overflow port on the outflow overflow plate. Then the water flows into the water storage tank from the inverted triangle overflow port on the outflow overflow plate.

[0118] The overflow channel is laid on the opposite side of the inflow channel of the drainage rain garden and the infiltration rain garden. It is about 30 cm wide and 30-40 cm deep. It is a small water storage tank. The rainwater in the drainage rain garden and the infiltration rain garden enters the corresponding overflow channel through the perforations. When there is enough water in the overflow channel, it flows out from the overflow channel.

[0119] The rainwater collection route is connected to the roof rainwater pipe. The rainwater collection route extends from under the corresponding eaves to the corresponding drainage type rainwater garden and the inflow weir of the infiltration type rainwater garden. The rainwater collection route is located below the ground, and sealed waterproof walls are laid radially around to form a water flow channel.

[0120] Rainwater collection route: a dedicated flow channel for receiving roof rainfall, with a longitudinal slope of 1%. In order to facilitate comparative test research and ensure that the rainfall conditions are the same, the present invention divides the roof runoff into two parts. The rainwater flows into the infiltration type rain garden through the infiltration type rain garden inlet channel 3 and the drainage type rain garden inlet channel 4, respectively.

[0121] The infiltration type rainwater garden inflow channel 3 and the drainage type rainwater garden inflow channel 4 are composed of a rectangular confluence trough with a width equal to that of the inflow channel and a rainwater garden inflow weir plate, and a paperless water level flow recorder is installed to record the inflow process; the triangular weir plate can not only reduce the confluence speed, but also detect the inflow volume and increase the soil infiltration time; (Note: In order to increase the operability and flexibility of the experiment, a movable weir plate is installed here. The weir plate is placed 0.3m away from the front of the weir. According to the meteorological forecast, the triangular weir plates of 30°, 45°, and 60° can be selected for flow monitoring. A movable grid filter trough is installed in the inflow trough with a mesh diameter of 0.5 to 1.5 cm to filter solid debris from entering the front of the weir, affecting the progress and accuracy of flow monitoring, and facilitating the rapid cleaning of the inflow channel after rain).

[0122] Water level monitor: mainly used to monitor the changes of groundwater in the rain garden before rainfall and explore its laws. It is set inside the rain garden to automatically monitor the changes of groundwater in the rain garden before and after rain.

[0123] Use Trime tubes to test soil moisture content: It is mainly used to monitor the changes in moisture content inside the rain garden before rainfall and explore its patterns. Trime tubes are installed inside the rain garden to automatically monitor the changes in soil moisture content before and after rain.

[0124] Infiltration type rain garden overflow channel 15, drainage type rain garden overflow channel 16: set at the end of the rain garden, receive the excess water after the rain garden treatment, and place the rain garden overflow weir plate 0.5m away from the rain garden, and install a paperless water level flow recorder 35 to record the outflow and change process (Note: a movable grid filter trough is installed in the overflow trough, with a mesh diameter of 0.5 to 1.5cm, which is used to filter solid debris before entering the weir, affecting the flow monitoring progress and accuracy, and is also convenient for the rapid cleaning of the inflow channel after rain);

[0125] Perforated pipe drainage channel 21: buried at 90-120 degrees at the bottom of the drainage rain garden, arranged parallel to the long axis of the rain garden, used to receive saturated water after soil infiltration. At the same time, in order to facilitate the collection of water samples for water quality monitoring, the bottom of the perforated pipe should extend about 20 cm from the main body of the rain garden; a movable perforated pipe overflow weir plate 22 is also placed 1 m away from the rain garden.

[0126] Reservoir 23: Considering that it is difficult to seamlessly connect with the traditional rainwater pipe system in the simulation test, the reservoir is added to collect the water treated by the two rain gardens. A pump is installed in the reservoir to control the depth of the water in the reservoir by automatically controlling the water level. The collected water can be used for ground irrigation, etc. When the rainfall is too heavy and the experimental reservoir exceeds the safe water level, the safety alarm sounds, the pumping work starts, and the pumping pipe is connected to the nearby urban pipe network;

[0127] Artificial red brick road 24 is a simple road paved inside the rain garden for experimenters to enter, which plays a role in protecting the surrounding vegetation from being trampled;

[0128] The groundwater level monitoring well 25 is mainly used to monitor the changes in the groundwater level around the rain garden before the rainfall and explore its laws. It is tested irregularly by the experimenters;

[0129] Experimental rainwater sampling platform 26: It is convenient for experimental personnel to collect rainwater samples from the perforated pipe outlet and inspect the sanitation and water pump in the reservoir at the same time;

[0130] Water level gauge: convenient for observing the changes in the water level of the rain garden aquifer;

[0131] The automatic water suction pump 40 is turned on when the water pressure reaches a certain high pressure limit value, and is turned off when the water pressure reaches a low pressure limit value, and the critical value can be flexibly designed.

[0132] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A composite rain garden that meets the requirements of multi-objective monitoring of urban runoff, comprising an infiltration rain garden (9) and a drainage rain garden (10), Features: The infiltration type rain garden (9) is connected to the rainwater collection route (2) via the infiltration type rain garden inflow channel (3), the drainage type rain garden (10) is connected to the rainwater collection route (2) via the drainage type rain garden inflow channel (4), the infiltration type rain garden (9) is connected to the reservoir (23) via the infiltration type rain garden overflow channel (15), the drainage type rain garden (10) is connected to the reservoir (23) via the drainage type rain garden overflow channel (16), an automatic water suction pump (40) is installed at the bottom of the reservoir (23), and the automatic water suction pump (40) is connected to the outside through a water pipe; The infiltration type rain garden inflow channel (3) is provided with a first inflow channel grid filter trough (5) and a first rain garden inflow weir plate (7), and the drainage type rain garden inflow channel (4) is provided with a second inflow channel grid filter trough (6) and a second rain garden inflow weir plate (8), the first rain garden inflow weir plate (7) and the second rain garden inflow weir plate (8) are arranged away from the direction of the rainwater collection route (2), and the first inflow channel grid filter trough (5) and the second inflow channel grid filter trough (6) are arranged close to the direction of the rainwater collection route (2); The infiltration type rain garden overflow channel (15) is provided with a first rain garden overflow weir plate (17) and a first overflow channel mesh filter trough (19); the drainage type rain garden overflow channel (16) is provided with a second rain garden overflow weir plate (18) and a second overflow channel mesh filter trough (20); the first rain garden overflow weir plate (17) and the second rain garden overflow weir plate (18) are arranged close to the water storage tank (23), and the first overflow channel mesh filter trough (19) and the second overflow channel mesh filter trough (20) are arranged away from the water storage tank (23); A perforated pipe drainage channel (21) is also provided on one side of the drainage type rain garden overflow channel (16); a perforated pipe overflow weir plate (22) is installed at the connection point between the perforated pipe drainage channel (21) and the water storage tank (23); and a perforated drainage pipe (39) is installed inside the perforated pipe drainage channel (21); The infiltration type rain garden (9) is internally installed with a first water level monitor (11) and a first trime pipe (13); the drainage type rain garden (10) is internally installed with a second water level monitor (12) and a second trime pipe (14); A groundwater level monitoring well (25) is provided on one side of the infiltration type rain garden (9). The infiltration type rain garden (9) is composed of an infiltration type rain garden planting soil layer (27) and an infiltration type rain garden covering soil layer (28); The drainage type rain garden (10) is provided with a drainage type rain garden planting soil layer (29), a drainage type rain garden biological filtration layer (30), a drainage type rain garden gravel layer (31), and a drainage type rain garden fine sand medium layer (32) in order from the ground surface downward; The interior of the drainage type rain garden (10) is paved with a composite impermeable geomembrane (33), and the edge is flush with the water storage layer of the drainage type rain garden (10) and hidden inside the slope. The bottom of the fine sand medium layer (32) of the drainage type rain garden is provided with a perforated drainage pipe (39) wrapped with a permeable geomembrane (34). The perforated drainage pipe (39) is buried in the middle position of the bottom of the drainage type rain garden (10) along the long axis direction of the drainage type rain garden (10).

2. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: The rainwater collection route (2) is arranged under the eaves of the house (1) and has the same length as the eaves, and is used to collect rainwater from the eaves.

3. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: An experimental rainwater sampling platform (26) is provided at one end of the water storage tank (23).

4. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: The outlet of the perforated drainage pipe (39) of the drainage type rain garden overflow channel (16) is arranged in the drainage groove of the perforated pipe drainage channel (21), and the outlet extends horizontally into the drainage groove by 18-20 cm, and the drainage groove is connected to the water storage tank (23).

5. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: The perforated drainage pipe (39) is provided with a plurality of 1 cm long and 3 mm wide holes around the pipe.

6. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: The rainwater collection route (2) is connected to the roof rainwater pipe of the house (1). The rainwater collection route (2) is located below the ground, and a sealed waterproof wall is laid radially around it to form a water flow channel, and a slope is set for the circulation of rainwater. A first paperless water level flow recorder (35) is fixedly installed inside the infiltration type rainwater garden overflow channel (15) and the drainage type rainwater garden overflow channel (16); a second paperless water level flow recorder (36) is fixedly installed inside the infiltration type rainwater garden inflow channel (3) and the drainage type rainwater garden inflow channel (4) to record the flow process. A second water level gauge (38) is installed on one side of the infiltration type rainwater garden inflow channel (3) and the drainage type rainwater garden inflow channel (4), and a first water level gauge (37) is installed on one side of the infiltration type rainwater garden overflow channel (15) and the drainage type rainwater garden overflow channel (16).

7. The composite rain garden that meets the requirements of multi-objective monitoring of urban runoff according to claim 1, Features: The first rain garden inflow weir plate (7), the second rain garden inflow weir plate (8), the first rain garden overflow weir plate (17), the second rain garden overflow weir plate (18) and the perforated pipe overflow weir plate (22) are all provided with an inverted triangle overflow port at the middle of the top end. The bottom angle of the inverted triangle overflow port of the first rain garden overflow weir plate (17), the second rain garden overflow weir plate (18) and the perforated pipe overflow weir plate (22) is 30 degrees, and the bottom angle of the inverted triangle overflow port of the first rain garden inflow weir plate (7) and the second rain garden inflow weir plate (8) is 60 degrees.

8. A construction method of a composite rain garden as described in claims 1-7, Features: The specific steps are as follows: Step 1: Construction method of drainage rain garden (10); Step 1.1: Site selection: Select a solid dirt ground near the house and the rainwater downpipe; Step 1.2: Drainage rain garden foundation pit: dig an elliptical drainage rain garden pit with a depth of 1-1.2 meters 2-3 meters away from the roof in the vertical direction of the ground. Form a vertical pit wall around the drainage rain garden pit, and dig a water storage pit next to the drainage rain garden pit; Step 1.3: Dig inlet and outlet channels: Dig an inlet channel on the side of the drainage rain garden pit close to the eaves, and dig an outlet channel on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30 cm higher than the surface of the drainage rain garden planting soil layer; Step 1.4: Lay out a drainage rain garden: Lay a 20cm thick fine sand medium layer on the geomembrane at the bottom of the pit, and lay a 110mm diameter perforated drainage pipe along the long axis of the ellipse. The outer layer of the perforated drainage pipe is wrapped with a permeable geomembrane of corresponding strength to prevent soil particles from blocking the pipe holes. The length of the overflow channel perforated drainage pipe is greater than the long axis of the ellipse, and a 20cm excess is reserved on the water outlet of the elliptical pit of the rain garden to discharge water into the drainage channel and enter the reservoir; Step 1.5: Drainage channel: dig a 0.4-meter-wide outlet channel at the outlet of the perforated drainage pipe at the bottom of the drainage rain garden with the same depth as the bottom of the rain garden pit. Build a concrete isolation wall to separate the outlet channel from the inside of the garden, leaving only the perforated drainage pipe position connected to the outside. Place an outlet triangular weir plate 1 meter away from the outlet channel for flow monitoring during rainfall. The weir angle should be 5 cm lower than the perforated drainage pipe outlet to prevent rainwater backflow due to untimely drainage. The outlet channel is located 1.2 meters below the ground, so an experimental rainwater sampling platform is built at the tail of the outlet channel to facilitate sampling during the experiment and water storage tank maintenance. Step 1.6: Setting of confluence channel: Dig a 40 cm wide concrete confluence channel along the eaves to ensure that the confluence channel is flat and the longitudinal slope of the road is less than 1%. Set up a water retaining slope 10 cm above the ground around the confluence channel to prevent rainwater from leaking sideways. Rainwater flows into the rain garden along the confluence channel. Step 1.7: Set up the inflow weir plate and overflow weir plate: The layout method is the same as that of the drainage channel. The difference is that in order to adapt to different rainfall intensities, the inflow weir plate is set as a removable movable weir plate. When the rainfall intensity is large, the weir angle can be flexibly changed to adjust the inflow flow to prevent overflowing; Step 2: Construction method of infiltration rain garden; Step 2.1: Site selection: Same drainage type rain garden, arranged in parallel with the drainage type rain garden; Step 2.2: Dig inlet and outlet channels: Dig a 40cm wide inlet channel on the side of the infiltration rain garden pit close to the eaves, and dig an outlet channel of the same width on the opposite side of the inlet channel, so that the bottom of the inlet and outlet channels are 20-30cm higher than the surface of the planting soil layer of the infiltration rain garden; Step 2.3: Dig a pit of the same area as the drainage rain garden and 1 meter deep. After digging, fill it with 30 cm of planting soil and 50 cm of covering soil. The remaining 20 cm is the reserved water storage depth. Step 2.4: Set up the inflow weir and overflow weir: The layout method is the same as that of the drainage rain garden; Step 2.5: Lay a 3-meter Trime pipe inside the garden, with the pipe opening 0.5 meters above the ground. The Trime pipe is used to monitor soil moisture before and after rain; Step 2.6: Install a groundwater level monitor inside the garden, with the pipe mouth 0.5 meters above the ground. The groundwater level monitor is used to monitor the soil moisture content before and after rain.

9. A method for testing a composite rain garden as claimed in claims 1 to 7, Features: The steps include: Step a: Determine the detailed inflow and outflow process of the infiltration type rain garden (9) and the drainage type rain garden (10): Place paperless water level flow recorders at the inflow channel and the overflow channel respectively, and calculate the absolute water pressure recorded by the paperless water level flow recorder and the atmospheric pressure to obtain the change of the water level height h of the triangular weir at different outflows. The data collection frequency is set to 1 minute and converted into instantaneous flow to accurately measure the inflow and outflow of the rain garden; the interception and reduction effects and differences of the two types of rain gardens on rainwater can be qualitatively analyzed; Triangular weir flow calculation formula: Where: Q is the wastewater flow rate, unit: m 3 / s; h is the geometric head of the weir, m, which is automatically recorded by a paperless water level flow recorder; θ is the weir angle, in degrees, where the inlet weir is 30-60 degrees, the outlet weir is 45 degrees, and the drainage weir is 30 degrees; μ is the flow coefficient, μ=0.6; g is the acceleration of gravity, g is 9.808m / s; Step b: Laying out the trime pipes of the drainage and infiltration rain gardens. Using detectors to automatically detect the changes in soil moisture content at different depths in the pipes before and after rain, quantitatively analyzing the physical process of the two types of rain gardens in terms of rainwater infiltration and retention rules during rainfall events and the effects on groundwater recharge, thus providing constructive suggestions for actual projects. Step c: Water quality monitoring: Arrange enough experimental personnel to collect water samples from the inflow, outflow and drainage outlets of the two rain gardens at the early, middle and late stages of rainfall, and monitor the pollutant indicators in the water samples. Compare and analyze the differences in the degradation rules of pollutants in different rain gardens during the same rainfall event, so as to explore the advantages and disadvantages and differences of rain gardens in terms of rainwater storage and flood control under single and combined situations, so as to study a more complete construction plan; Step d: Detect and record the infiltration performance of the drainage rain garden (10) and the infiltration rain garden (9): In order to avoid the influence of soil infiltration variability, the overall infiltration characteristics of the rain garden will be obtained by the water balance method. When the surface of the rain garden is flooded, evapotranspiration during rainfall can be ignored. The water balance items in the rain garden are inflow, outflow, infiltration and change of water depth in the garden. The inflow and outflow are monitored by triangular weirs, and the change of water depth in the rain garden is obtained by reading the water gauge installed in the garden. Therefore, the total inflow and outflow and the change of water depth in the rain garden within a certain period of time are monitored to obtain the infiltration rate of the rain garden. The soil infiltration rate (K) is: W in is the total inflow during the period, in m 3 ; ΔH is the change in water depth in the garden during the period, in m; A is the area of ​​the rain garden, in m 2 ; W out The total outflow volume during the period, in m 3 ; According to the actual rainfall situation, the infiltration rate is measured in 2-3 groups as much as possible during each rainfall process, with the time interval Δt of each group controlled to be 2 minutes, and the total measurement time of each group is 30 minutes; by monitoring the soil infiltration capacity and particle composition changes in the rain garden, the sustainability of the infiltration capacity and operation effect of the rain garden during long-term operation is studied; Step e: Comparison: By monitoring the soil moisture content at the infiltration point of the rain garden and the changes in the surrounding groundwater level, the impact of the concentrated infiltration of the rain garden on the groundwater can be obtained and reasonable protection measures can be given; by monitoring the water samples of the two rain gardens during rainfall and testing the groundwater quality before and after rainfall, the physical relationship between the changes in the concentration of different pollutants and the concentrated infiltration recharge can be established, and the changing laws of pollutant removal rates in different rain gardens can be studied.

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