Detail of GB 50400-2016

Introduction of GB 50400-2016

Technical code for rainwater management and utilization of building and sub-district 1 General provisions 1.0.1 In order to build a low-impact development system for urban source rainwater, develop or repair the water environment and ecological environment, realize total runoff control, peak runoff control, and runoff pollution control of source rainwater, and make low-impact development rainwater system projects in buildings, sub-districts and factories technologically advanced, economically reasonable, safe and reliable, this code is developed. 1.0.2 This code is applicable to the planning, design, construction, acceptance, and operation management of rainwater management and utilization engineering in sponge-type civil buildings and sub-districts, industrial buildings, and factories. This code is inapplicable to rainwater utilization engineering where rainwater is used as a source of drinking water. 1.0.3 Rainwater management and utilization engineering shall reasonably adopt various technologies for developing rainwater systems with low impact according to the specific conditions of the engineering, local water resources conditions, and economic development level. 1.0.4 Rainwater management and utilization engineering may adopt technical measures such as infiltration, stagnation, detention, purification, use, and drainage. 1.0.5 Planning and design stage documents shall include the contents on rainwater management and utilization. Rainwater management and utilization equipment shall be planned, designed, constructed, and put into use simultaneously together the main engineering of the project. 1.0.6 Rainwater management and utilization engineering shall take measures to ensure personal safety, use, and maintenance safety. 1.0.7 Rainwater management and utilization engineering shall be designed in conjunction with outdoor general plan, landscape, architecture, water supply and drainage, and other specialties. 1.0.8 The planning, design, construction, acceptance, operation management of rainwater management and utilization engineering of buildings and sub-districts shall also meet the requirements of the relevant current national standards in addition to complying with this code. 2 Terms and symbols 2.1 Terms 2.1.1 rainwater management and utilization general term for total runoff, peak runoff, and runoff pollution control equipment, including rainwater infiltration (permeability), harvesting and reuse, detention and controlled drainage, etc. 2.1.2 volume capture ratio of annual rainfall percentage of the cumulative annual managed rainfall in the site in the total annual rainfall according to the statistical analysis and calculation of multi-year daily rainfall 2.1.3 漏掉了 2.1.4 underlying surface a general term for surface receiving water including roof, ground, water surface, etc. 2.1.5 permeability coefficient of soil steady infiltration velocity of water per unit hydraulic slope 2.1.6 pluviometric runoff coefficient ratio of the total amount of runoff produced by rainfall to the total amount of rainfall over a set time 2.1.7 impervious surface impermeable ground formed by hardening the natural ground through artificial actions 2.1.8 initial runoff pluviometric runoff with certain thickness at the initial stage of rainfall 2.1.9 initial rainwater removal equipment facility that utilizes rainfall amount and rainwater runoff thickness to control initial runoff discharge including automatic control removal well, infiltration-removal well, removal pool, etc. 2.1.10 infiltration-removal well device with a certain storage volume and sewage interception function to infiltrate the initial runoff into the underground 2.1.11 infiltration equipment facility that stores rainwater runoff flow and perform infiltration, including infiltration ditch, infiltration pool, infiltration well, pervious pavement, etc. 2.1.12 infiltration pool buried pool where rainwater infiltrates through the side walls and bottom of the pool 2.1.13 infiltration well facility where rainwater infiltrates through sidewalls and bottoms of the well 2.1.14 infiltration-drainage pipe system system in which infiltration manholes and infiltration pipes are used to infiltrate rainwater into the underground in an organized way, and rainwater exceeding the infiltration design standard is discharged from pipe trench 2.1.15 pervious pavement ground pavement structure composed of permeable top layer, base layer, sub-base layer, etc. which can store and infiltrate the rainfall it receives 2.1.16 grass swale facility with vegetation planted in swale on the surface, which can intercept rainwater and infiltrate it, or transfer rainwater and use vegetation to purify it 2.1.17 infiltration trench rainwater drain or ditch with infiltration function 2.1.18 infiltration manhole pipe inspection and maintenance device with penetration function and certain grit settling volume 2.1.19 collect-infiltration manhole pipe inspection and maintenance device with a top cover that collects ground rainwater, which has penetration function and a certain grit settling volume 2.1.20 rainwater storage equipment facility for storing untreated rainwater 2.1.21 wet pond landscape water body with rainwater detention, control and purification functions, which uses rainwater as the main water replenishment source 2.1.22 detention and controlled drainage equipment facility that stores rainwater for a certain period of time, reduces the peak runoff of rainwater discharged downstream, and extends the discharge time 2.1.23 bioretention system, bioretention cell facility for detention storage, infiltration and purification of runoff rainwater through plants, soil and microbial systems 2.2 Symbols 2.2.1 Flow, water amount Q——inflow of regulating and detention pool; Q ——design flow of outlet pipe; Qy——treatment capability of equipment; Vh——water storage capacity of rainwater storage equipment of harvesting and reuse system; VL——amount of rainwater intercepted by rainwater management and utilization equipment; VL1——amount of rainwater intercepted by infiltration equipment; VL2——amount of rainwater intercepted by harvesting and reuse equipment; VL3——amount of rainwater intercepted by detention and controlled drainage equipment; Vs——amount of rainwater detained by detention infiltration system; Vt——water storage capacity of rainwater storage equipment of detention and controlled drainage system; W——total amount of rainwater runoff that needs to be managed and utilized; W1——design runoff of rainwater on the catchment surface of infiltration equipment; W2——design runoff of rainwater on the catchment surface of harvesting and reuse system; Wc——water inflow of infiltration equipment; Ws——amount of infiltration; Wi——initial runoff removal flow; Wp——total amount of water excluded from development site; Wx1——amount of rainwater infiltrated when the amount of rainwater accumulated in the infiltration equipment reaches the maximum value; Wy——maximum daily water consumption of the reuse system; q——design rainstorm intensity; qc——intensity of rainstorm corresponding to the runoff duration of the infiltration equipment; qi——maximum daily water quota for certain type of water users. 2.2.2 Head loss, geometric characteristics As——effective permeation area; F——area of impervious catchment surface; F0——direct water receiving area of infiltration equipment; Fy——catchment area received by infiltration equipment; Fz——total area of development site; hy——daily rainfall in design; hp——daily rainfall in drainage design; δ——initial runoff removal thickness; 2.2.3 Calculation coefficients and others A, b, c, n——parameters of local rainfall; J——hydraulic gradient; K——permeability coefficient of soil; fk——rainwater management and utilization rate of development site; ni——number of certain type of water users; α——comprehensive safety coefficient; Ψ0——runoff coefficient corresponding to the managed runoff peak, which shall meet the local planning control requirements; Ψc——pluviometric runoff coefficient; Ψz——comprehensive pluviometric runoff coefficient of development site. 2.2.4 Time P——design recurrence interval; T——daily operating time of rainwater treatment equipment; t——duration of rainfall; t1——catchment time of catchment surface; t2——time of flow for rainwater in pipe trench; tc——runoff duration of the infiltration equipment; tm——water storage duration of regulating and detention pool; ts——infiltration duration; ty——water use duration. 3 Water quantity and water quality 3.1 Rainfall and rainwater quality 3.1.1 Rainfall shall be determined according to the local rainfall data of more than 20 years. When the data is lacking, the values in Annex A to this code may be used. 3.1.2 The total annual rainwater runoff in the development land shall be managed, and the management rate and corresponding design rainfall shall meet the requirements of local sponge city planning management indicators. 3.1.3 The peak value of rainwater runoff shall be managed in the development land, and the total amount of rainwater runoff that needs to be managed and utilized shall be calculated using the following equation. When hydrological and rainfall data are available, it can also be determined according to the analysis of multi-year rainfall data. W=10(Ψc-Ψ0)hyF (3.1.3) where, W——the total amount of rainwater runoff that needs to be managed and utilized, m3; Ψc——pluviometric runoff coefficient; Ψ0——the runoff coefficient corresponding to the managed runoff peak, which shall meet the local planning management requirements; hy——the daily rainfall in design, mm; F——the catchment area of impervious surface, hm2, which shall be calculated according to the horizontal projected area of the impervious catchment surface. 3.1.4 The pluviometric runoff coefficient should be adopted according to Table 3.1.4, and the comprehensive runoff coefficient of the catchment area shall be calculated according to the weighted average of the type of underlying surface.   Table 3.1.4 Rainfall runoff coefficient Type of underlying surface Pluviometric runoff coefficient, ψc Hard roof, unstoned flat roof, asphalt roof 0.80~0.90 Flat roof paved with stones 0.60~0.70 Green roof 0.30~0.40 Concrete and asphalt pavement 0.80~0.90 Pavement with rubbles, etc. 0.50~0.60 Dry brickwork and gravel pavement 0.40 Unpaved soil pavement 0.30 Green land 0.15 Water surface 1.00 Green land covered with soil for underground buildings (thickness of covering soil≥500 mm) 0.15 Green land covered with soil for underground buildings (thickness of covering soil< 500 mm) 0.30~0.40 Pervious pavement ground 0.29~0.36 3.1.5 The daily rainfall in design shall be determined according to the annual maximum 24-hour rainfall, which can be determined according to the provisions of 3.1.1 of this code or local rainfall data, and shall not be less than the design rainfall corresponding to the local total annual runoff management rate. 3.1.6 The area of impervious catchment surface shall be calculated according to the sum of the areas of impervious surface, non-green roof, and water surface, and the area of pervious pavement ground shall be deducted. 3.1.7 The water quality of roof rainwater after initial runoff removal should be determined based on local measured data. When there is no measured data, the following empirical values may be used: CODCr 70 mg/L to 100 mg/L; SS 20 mg/L-40 mg/L; Chroma 10 degrees~40 degrees. 3.1.8 The total amount of pollutants discharged into municipal rainwater pipes should be managed. The quality of rainwater discharged into urban surface water bodies shall meet the water quality requirements of the water body. 3.2 Rainwater resource utilization and water quality 3.2.1 The maximum daily water consumption for greening, road and square watering, garage floor washing, vehicle washing, circulating cooling water replenishment, etc. shall be implemented in accordance with the provisions of the current national standard GB 50015 Standard for design of building water supply and drainage, and the average daily water consumption shall be implemented in accordance with the current national standard GB 50555 Standard for water saving design in civil building. 3.2.2 The maximum daily flushing water consumption for various types of buildings shall be implemented in accordance with the current national standard GB 50336 Standard for design of building reclaimed water system. 3.2.3 The water replenishment amount of landscape water body shall be comprehensively determined according to local water surface evaporation and water infiltration, water treatment self-consumption and other factors. 3.2.4 The water quality of the reused rainwater centralized supply system shall be determined according to the use, CODCr and SS indicators shall be as specified in Table 3.2.4, and other indicators shall comply with the provisions of current relevant national standards. Table 3.2.4 CODCr and SS indicators of reused rainwater Item indicator Replenishment of recirculated cooling system Ornamental water landscape Recreational water landscape Greening Vehicle flushing Road sprinkling Toilet flushing CODcr(mg/L) ≤30 ≤30 ≤20 - ≤30 - ≤30 SS(mg/L) ≤5 ≤10 ≤5 ≤10 ≤5 ≤10 ≤10 3.2.5 When rainwater is used for multiple purposes at the same time, its water quality shall be determined according to the highest water quality standard. 3.2.6 The daily rainwater infiltration (utilization) amount of infiltration equipment shall be calculated using the following equation: (3.2.6) where, Ws——the amount of infiltration, ｍ3; α——the comprehensive safety coefficient, generally taken as 0.5~0.8; K——the permeability coefficient of soil, ｍ/s; J——the hydraulic gradient, generally taken as J=1.0; As——the effective permeation area, m2; ts——the infiltration duration, s, taken by 24 hours. 3.2.7 The permeability coefficient of soil shall be determined according to the measured data. It may be selected according to 3.2.7 if the measured data are not available.   Table 3.2.7 Permeability coefficient of soil Stratum Stratigraphic particle size Permeability coefficient, K Particle size (mm) Weight (%) (m/s) (m/h) Clay <5.70× 10-8 Silty clay 5.70×10-8~1.16×10-6 Floury soil 1.16×10-6~5.79×10-6 0.0042~0.0208 Silt >0.075 >50 5.79×10-6~1.16×10-5 0.0208~0.0420 Fine sand >0.075 >85 1.16×10-5~5.79×10-5 0.0420~0.2080 Medium sand >0.25 >50 5.79×10-5~2.31×10-4 0.2080~0.8320 Homogeneous medium sand 4.05×10-4~5.79×10-4 Coarse sand >0.50 >50 2.31×10-4~5.79×10-4 3.2.8 The effective permeation area of the infiltration equipment shall be determined according to the following requirements: 1 The horizontal infiltration area is calculated according to the projected area; 2 The vertical infiltration area is calculated as 1/2 of the vertical area corresponding to the effective water level height; 3 The inclined infiltration area is calculated according to the actual area of the inclined surface corresponding to 1/2 of the effective water level height; 4 The top area of infiltration equipment buried underground is not included. 4 Rainwater management and utilization system 4.1 General requirements 4.1.1 Rainwater management and utilization system shall manage the total annual runoff and peak discharge runoff of perennial rainfall after the construction or reconstruction of the site to the level before construction and development, and shall comply with 3.1.2 and 3.1.3 of this code. 4.1.2 As for rainwater management and utilization, the following shall be adopted: a single system or a combination of multiple systems in rainwater infiltration system, harvesting and reuse system, detention and controlled drainage system, and the following provisions shall be followed: 1 The rainwater infiltration system shall consist of rainwater harvesting, storage and infiltration equipment; 2 The harvesting and reuse system shall be equipped with facilities such as rainwater harvesting, storage, treatment and reuse water pipe networks; 3 The detention and controlled drainage system shall be equipped with rainwater harvesting, regulating and detention equipment, discharge pipelines and other facilities. 4.1.3 The selection of rainwater management and utilization system shall meet the following requirements: 1 The permeability coefficient of soil of the infiltration system shall be between 10-6 m/s and 10-3 m/s, and the distance between the infiltration surface and the groundwater level shall be greater than 1.0 m, and the infiltration surface shall be calculated from the lowest point; 2 The harvesting and reuse system should be used in areas with average annual rainfall greater than 400 mm; 3 The detention and controlled drainage system should be used in places with flood control and drainage requirements or places where rainwater resource utilization is restricted. 4.1.4 The layout of rainwater management and utilization equipment shall meet the following requirements: 1 The site design and architectural layout shall be based on the current terrain and landforms, and the existing water bodies, wetlands, ponds, ditches, etc. within the site shall be protected and reasonably utilized; 2 The spatial layout of impervious surface and green spaces shall be optimized, and green spaces that can absorb runoff rainwater should be arranged around buildings, squares, and roads; 3 The vertical design of buildings, roads, green spaces, etc. shall be conducive to runoff flow into rainwater management and utilization equipment. 4.1.5 Rainwater infiltration sites shall have detailed geological survey data, which shall include the distribution of regional stagnant water layer, soil types and corresponding permeability coefficients, groundwater dynamics, etc. 4.1.6 Rainwater infiltration shall not cause geological disasters and damage buildings. Rainwater infiltration system shall not be used in the following places: 1 Places that may cause collapse and landslide disasters; 2 Places that cause harm to the living environment and natural environment; 3 Special soil geological sites such as self-weight collapsible loess, expansive soil and high saline soil. 4.1.7 Rainwater harvesting and reuse systems shall not be used for rainwater from infectious disease hospitals, rainwater from sites with serious surface pollution such as heavy metal pollution and chemical pollution. For buildings and sub-districts with special pollution sources, rainwater management and utilization projects shall be subject to special demonstration. 4.1.8 Construction land equipped with rainwater management and utilization system shall be equipped with rainwater drainage measures, and ground elevation control shall be carried out to prevent rainwater from outside the area from flowing into the land. The vertical planning and design of urban land shall comply with the requirements of the national professional standard CJJ 83 Code for vertical planning on urban and rural development land. 4.1.9 The rainwater management and utilization system shall not cause harm to the soil environment, underground aquifer water quality, public health and environmental sanitation, and shall be convenient for maintenance and management. The selection of plants in landscape shall meet the needs of rainwater management and utilization. 4.1.10 Low water quality standard water in the reused water supply pipe network shall not enter the high water quality standard water system. 4.1.11 Rainwater structures and pipelines shall comply with the current national standards GB 50069 Structural design code for special structures of water supply and waste water engineering and GB 50015 Standard for design of building water supply and drainage.

Contents of GB 50400-2016

Foreword i 1 General provisions 2 Terms and symbols 2.1 Terms 2.2 Symbols 3 Water quantity and water quality 3.1 Rainfall and rainwater quality 3.2 Rainwater resource utilization and water quality 4 Rainwater management and utilization system 4.1 General requirements 4.2 System type selection 4.3 System equipment calculation 5 Rainwater harvesting and exclusion 5.1 Roof rainwater harvesting 5.2 Harvesting rainwater from impervious surface 5.3 Rainwater removal 5.4 Rainwater exclusion 6 Rainwater infiltration 6.1 General requirements 6.2 Infiltration equipment 7 Rainwater storage and reuse 7.1 General requirements 7.2 Storage equipment 7.3 Rainwater reuse water supply system 7.4 System control 8 Water treatment 8.1 Water treatment process 8.2 Treatment facilities 8.3 Rainwater treatment station 9 Detention and controlled drainage 10 Construction and acceptance 10.1 General requirements 10.2 Buried infiltration equipment 10.3 Permeable ground 10.4 Assembled combination pool 10.5 Pipe laying 10.6 Equipment installation 11 Completion acceptance 11.1 Hydrostatic test 11.2 Acceptance 12 Operation management Annex A Rainfall data of the major cities in China Explanation of wording in this code