Applying the Chicago hyetograph for intense rainfall equations of the LnLn type

The Chicago Method is one of the most common methods to determine design rainfall hyetographs for urban drainage infrastructures. Among the advantages of the method is that it is easy to apply and is based on traditional IDF equations. Nevertheless, applications to other IDF equation models presents some limitations. The aim of the present study was to adapt and apply the Chicago hyetograph method with intense rainfall equations of the LnLn type. Equations to estimate rainfall intensity before and after peak duration were presented. In addition, equations to obtain accumulated rainfall before and after peak rainfall volumes were adapted. With this information, we were able to obtain rainfall blocks for each interval of the hyetograph. The method was applied to determine the hyetograph based on the intense rainfall equation for the town of Piracicaba, Sao Paulo, Brazil. The equations presented here can be implemented on electronic spreadsheets or in programming routines, hence allowing Engineering professionals to apply the most adequate methods to local data.