If the watershed is small, you can use the Rational Method to calculate the design flow rate. If the area is large or you need hydrographs for designing a detention basin, the Flood Control District can calculate the hydrographs for you. You need to request a HYDRO6 submittal package. There is a fee for the District to calculate the flows for you. Contact the Hydrology Section at the number below and they can e-mail the HYDRO6 instructions and submittal package to you. You may also purchase the submittal package at the front counter of the Public Works Department office (255 Glacier Drive, Martinez, CA 94553).