Technical Support
National Standard Architectural Design Atlas
National Standard Design Atlas for Architectural Construction, 24J306 (replacing 07J306) – Title: Window Wells, Equipment Lifting Openings, Drainage Ditches, and Sump Pits – China Academy of Building Research
Calculate the catchment area and stormwater runoff volume.
According to GB 50014-2006 “Code for Outdoor Drainage Design,” the design rainwater runoff is calculated using the following formula:
Q — Design rainwater runoff (L/s)
F — Catchment area (L×W) m²
q — Design storm intensity L/(s·hm²)
ψ — Runoff coefficient, which can be referenced from the table below.
Note:
Q represents the design rainwater runoff that the drainage ditch in a given section is required to convey. If you need to determine the runoff capacity per meter of the ditch, divide Q by the total designed length of the ditch.
F refers to the catchment area of the section requiring drainage (length L × width W).
q is the local storm intensity; when performing calculations, it should be determined in accordance with the design code. Refer to resources such as the “Building Water Supply and Drainage Design Manual” to find storm intensity tables for different regions and return periods.
ψ is the runoff coefficient, which varies depending on the type of surface material. Specific values can be obtained by referring to the table below.
Determination of Drainage Channel Size Calculation
Once the rainwater discharge rate Q specified in ① has been determined, the appropriate drainage ditch dimensions can be selected by taking into account the aforementioned factors. These dimensions are expressed in terms of the internal width and internal depth of the ditch, which are used to adjust the cross-sectional area of the flow passage and thereby select the suitable ditch configuration.
● Our prefabricated drainage ditches typically have integer internal widths, such as 100 mm, 200 mm, or 300 mm.
● The external width and height of the drainage ditch vary depending on the product specification; therefore, during hydraulic calculations, the internal width and internal depth should be used as the reference values.
Our company’s design engineers can calculate the rainwater discharge per meter for each ditch specification under different flow lengths. By combining this information with the required rainwater discharge specified in ①, the appropriate ditch dimensions can be selected.
After determining the required rainwater discharge for surface water in area ①, we can assist you in selecting the appropriate ditch dimensions.
Load-bearing Requirements for Drainage Channel
Drainage Channel installed outdoors must, without exception, be designed to safely withstand the loads imposed by pedestrian and vehicular traffic.
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