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In Japan, four rainfall intensity formulas (Talbot, Kuno-Ishiguro, Cleveland, Sherman) are used in sewerage planning, including stormwater drainage. According to a survey report by the Ministry of Land, Infrastructure, Transport, and Tourism, these four formulas are adopted in 98.9% of regions across the country.
When formulating exterior plans for development areas, Japanese customers are interested in InfoDrainage. Whether the rainfall intensity formulas that are standardly used in Japan are incorporated is a crucial factor for adoption.
Name of Formulas |
General Form (One-Line Notation) |
Remark |
Kuno-Ishiguro |
i = A / (t ^ n + B) |
Most versatile form in Japan |
Talbot |
i = A / (t + B) |
Equivalent to Kuno-Ishiguro with n=1 |
Cleveland |
i = A / (t ^ 0.5 + B) |
Equivalent to Kuno-Ishiguro with n=0.5 ( \sqrt{t}). |
Sherman |
i = A / (t ^ n) |
Equivalent to Kuno-Ishiguro with B=0. |
These four formulas are structurally similar to the existing Chinese rainfall intensity formula, however, the their differences and the requirements for execution are as follows.
Features |
Chinese formula |
Japanese formula |
Request |
Return Period (P) Management |
P is embedded within the formula. |
P is external to the formula. A distinct set of coefficients ( A, B, n ) is used for each required 'P'. |
UI must allow the user to define and select different coefficient sets corresponding to the required 'P' (e.g., 5-year, 10-year). |
Hyetograph Generation |
Chicago Method ( r coefficient) creates a continuous curve. |
Block Rearrangement Method (Alternating Block) uses discrete blocks ( \Delta t ) that are rearranged. |
Utilize the existing Chicago Method logic, but prioritize the Center Concentration Type (peak in the middle, conceptually r \approx 0.5 ) as the standard option to meet Japanese design criteria. |
