Key points of sponge city specification


Release time:

2016-04-15

Author:

Shandong Xindadi Group

Source:

Key points of sponge city specification

1. Permeable pavement
Permeable brick pavement, permeable cement concrete pavement and permeable asphalt concrete pavement, grass brick, cobblestone and gravel pavement in garden pavement also belong to permeable pavement.
(1) When the potential risk of permeable pavement to the strength and stability of road subgrade is large, semi-permeable can be used.
(2) When the permeability of the land is limited, drainage pipes or drainage boards should be set up in the permeable base of the permeable pavement.
(3) When the permeable pavement is set on the roof of the basement, the thickness of the roof covering soil should not be less than 600mm, and a drainage layer should be set.
 
2. Sunken green space
The sinking depth refers to the average depth of the sunken green space lower than the surrounding paved ground or roads. The sunken green space area with a sinking depth of less than 100 mm is not involved in the calculation (subject to local soil permeability and other conditions, except for infiltration facilities with limited sinking depth). For water surface facilities such as wet ponds and rainwater wetlands, it refers to the regulated storage depth.
Permeable pavement rate = Permeable pavement area/total hardened ground area;
Green Roof Rate = Green Roof Area/Total Building Roof Area.
(1) The concave depth of sunken green space should be determined according to plant flooding tolerance and soil permeability, generally 100-200mm.
(2) Overflow ports (such as rainwater inlets) should be set in sunken green space to ensure the overflow discharge of runoff during rainstorm. The top elevation of overflow ports should generally be 50-100mm higher than that of green space.
 
3. Bioretention facilities
(1) For seriously polluted catchment areas, grass ditches, vegetation buffer zones or sedimentation tanks shall be used to pre-treat runoff rainwater to remove large particles of pollutants and slow down the flow rate; measures such as flow abandonment and salt discharge shall be taken to prevent high-concentration pollutants such as snow melting agents or petroleum from invading plants.
(2) Roof runoff rainwater can be connected to the bioretention facility through the rain-fall pipe, and road runoff rainwater can enter through the kerbstone gap. The size and quantity of the kerbstone gap shall be determined by calculation according to the longitudinal slope of the road.
(3) When the bioretention facilities are applied to the road green belt, if the longitudinal slope of the road is greater than 1%, a water retaining weir/abutment should be set to slow down the flow rate and increase the rainwater infiltration. The part of the facilities close to the roadbed shall be treated with anti-seepage to prevent the impact on the stability of the roadbed.
(4) Overflow facilities shall be set up in bioretention facilities, such as overflow standpipe, cover grate overflow well or rainwater inlet, etc. The top of overflow facilities shall generally be 100 mm lower than the catchment surface.
(5) Bioretention facilities should be distributed and the scale should not be too large, and the ratio of bioretention facility area to sink surface area is generally 5%-10%.
(6) Permeable geotextile shall be set on the outside and bottom of the structural layer of complex bioretention facilities to prevent the invasion of surrounding original soil. If it is assessed that the seepage will cause collapse risk to the surrounding buildings (structures), or if the bottom effluent is to be collected and recycled, impermeable membranes can be installed at the bottom and surrounding of the bioretention facility.
(7) The depth of aquifer of bioretention facilities shall be determined according to the flooding tolerance of plants and soil permeability, generally 200-300mm, and shall be set at an ultra-high of 100mm; The type and depth of medium in soil replacement layer shall meet the requirements of effluent water quality, and shall also meet the technical requirements of plant planting and landscaping maintenance management. In order to prevent the loss of medium in soil replacement layer, permeable geotextile isolation layer is generally set at the bottom, sand layer (fine sand and coarse sand) with a thickness of not less than 100 mm can also be used instead. The gravel layer plays a role of drainage, with a thickness of 250-300mm in general. A perforated drainage pipe with a pipe diameter of 100-150mm can be buried at the bottom of the gravel layer. The gravel shall be cleaned and the particle size shall not be less than the aperture of the perforated pipe. In order to improve the storage regulation of bioretention facilities, a certain thickness, gravel reservoir can be added at the bottom of perforated pipe.
 
4, infiltration pond (depression, mainly infiltration and essence, no rain call)
(1) Pre-treatment facilities such as grit chamber and front pond shall be set before the infiltration pond to remove large particle pollutants and slow down the flow rate; in cities with snowfall, measures such as flow abandonment and salt discharge shall be taken to prevent snow melting agent from harming plants.
(2) The slope of the side slope of the infiltration pond (vertical: horizontal) is generally not more than 1:3, and the water level from the pond bottom to the overflow water level is generally not less than 0.6 m.
(3) The bottom structure of the infiltration pond is generally 200-300mm planting soil, permeable geotextile and 300-500mm filter medium layer.
(4) The emptying time of the infiltration pond shall not be greater than 24 h. The infiltration pond shall be provided with overflow facilities, which shall be connected with the urban rainwater drainage system and the over-standard rainwater runoff drainage system, and the outer perimeter of the infiltration pond shall be provided with safety protection measures and warning signs.
 
5, wet pond (rainwater storage, there is a regulation volume of rainwater reuse)
(1) The water inlet and overflow outlet shall be provided with energy dissipation facilities such as gravel and energy dissipation sill to prevent water scouring and erosion.
(2) The front pond is a pretreatment facility for wet pond, which plays a role in precipitating large particle pollutants in runoff; the bottom of the pond is generally of concrete or block stone structure, which is convenient for dredging; the front pond should be provided with dredging channels and protective facilities, and the revetment should be in the form of ecological soft revetment, and the slope gradient (vertical: horizontal) is generally 1:2-1:8; the volume of the sedimentation area of the front pond shall be determined according to the dredging period and the SS pollutant load of the incoming runoff rainwater.
(3) The main pond generally includes the permanent volume and storage volume below the normal water level, and the water depth of the permanent volume is generally 0.8-2.5 m; The storage volume is generally determined according to the "unit area control volume" proposed by the relevant planning of the region. The wet pond with peak flow reduction function also includes an adjustable volume, which should be emptied within 24-48 h; the aquatic plant planting area (rainwater wetland) should be set between the main pond and the front pond, the main pond revetment should be ecological soft revetment, and the slope gradient (vertical: horizontal) should not be greater than 1:6.
(4) The overflow outlet includes overflow standpipe and spillway, and the drainage capacity should be determined according to the drainage capacity of downstream rainwater pipe channel or over-standard rainwater runoff discharge system.
(5) Safety protection and warning measures such as guardrails and warning signs shall be provided for wet ponds.
 
6. Rainwater wetland
(1) The water inlet and overflow outlet shall be provided with energy dissipation facilities such as gravel and energy dissipation sill to prevent water scouring and erosion.
(2) Pre-ponds shall be set up for pre-treatment of runoff rainwater in rainwater wetlands.
(3) Swamp area includes shallow swamp area and deep swamp area, which is the main purification area of rainwater wetland. The water depth range of shallow swamp area is generally 0-0.3 m, and that of deep swamp area is generally 0.3-0.5 m. According to water
Different types of aquatic plants are grown deep.
(4) The regulated volume of rainwater wetland should be emptied within 24h.
(5) The water tank mainly plays the role of preventing the resuspension of sediment and reducing the temperature. The water depth is generally 0.8-1.2 m, and the volume of the water tank is about 10% of the total volume (excluding the regulated volume).
 
7. Grass planting ditch
(1) Shallow ditch section form should adopt inverted parabola, triangle or trapezoid.
(2) The slope gradient (vertical: horizontal) of the grass planting ditch should not be greater than 1:3, and the longitudinal slope should not be greater than 4%. When the longitudinal slope is large, it should be set as stepped grass planting ditch or set energy dissipation platform sill in the middle.
(3) The maximum velocity of the grass planting ditch should be less than 0.8 m/s, and the Manning coefficient should be 0.2-0.3.
(4) The height of vegetation in the transfer type grass planting ditch should be controlled at 100-200mm.
 
8. Seepage pipe/canal
(1) Pretreatment facilities such as grass planting ditch and sedimentation (sand) pool shall be set up for seepage pipe/canal.
(2) The opening rate of seepage pipe/canal should be controlled between 1% and 3%, and the porosity of sand-free concrete pipe should be greater than 20%.
(3) The laying slope of seepage pipe/canal shall meet the requirements of drainage.
(4) Gravel or other porous materials shall be filled around the seepage pipe/canal. The gravel layer shall be covered with permeable geotextile, and the lap width of geotextile shall not be less than 200mm.
(5) When the seepage pipe/canal is set under the driving road surface, the covering depth shall not be less than 700mm.
 
9. Vegetation buffer zone
The vegetation buffer zone is a vegetation zone with a relatively slow slope. The surface runoff velocity is slowed down by vegetation interception and soil infiltration, and some pollutants in the runoff are removed. The slope of the vegetation buffer zone is generally 2%-6%, and the width should not be less than 2 m.
 
10. Initial rainwater drainage facilities
Common initial abandonment methods include volumetric abandonment, small tube abandonment (water flow switching method), etc. It is suitable for the front end of low-impact development facilities such as rain-fall pipes for roof rainwater and centralized entrances for runoff rainwater.

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