The Rziha formula has long been a puzzle. Adopted as the formula to estimate the time of concentration in the legal Regulations of Soil and Water Conservation (RSWC) in Taiwan, its source could never be identified, nor
has it ever been cited in international mainstream hydrological circles, except in Japan. This study investigated source documents from Japan, Germany, and Austria to uncover the story behind the formula; his investigation revealed that it bears no association to Rziha, but should instead be called the Bavarian (Bayern) conventional formula. The Kraven formula, which appeared alongside the Rziha formula in the 2014 Handbook of Soil and Water Conservation, has no connection to Kraven but is instead a set of data proposed by Rziha. These two ghost formulas have long been neglected in the research literature, which instead practiced blind obedience to the authority of Taiwanese academia. With the advance of hydrological theories, practitioners need no longer rely on empirical formulas but can estimate time of concentration using the kinematic wave model or numerical simulation combined with digital terrain models. Reflecting on the attitude of academic research, the RSWC is recommended to include only guiding principles and reserve the ever-changing formulas for the Handbook.
Key Words: Time of concentration, Rziha formula,Regulations of Soil and Water Conservation