When conducting a hydrology study in California, the primary goal is to come up with a design flow rate or volume from an estimated storm event. Hydrologic data collected over the past many decades is used to make the computations, which are then used to predict future events. Both the Rational and Modified Rational Methods are utilized for rainfall. There is no storage volume information for the Rational Methods, but the Modified Rational Method relies on historical rainfall records to determine the time of concentration and intensity during a storm period. Detailed information about rainfall isohyets may be found in California, which provides a visual representation of rainfall depth for some time. The isohyets are influenced by physical variables, such as elevation from sea level and soil conditions. For example, higher elevations receive more rain than lower ones. An area’s design storm can be calculated by multiplying the unit hyetograph by its rainfall depth and concentration.