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Cumulative frequency is also called frequency of non-exceedance. Cumulative frequency analysis is performed to obtain insight into how often a certain phenomenon (feature) is below a certain value. This may help in describing or explaining a situation in which the phenomenon is involved, or in planning interventions, for example in flood ...
The theoretical return period between occurrences is the inverse of the average frequency of occurrence. For example, a 10-year flood has a 1/10 = 0.1 or 10% chance of being exceeded in any one year and a 50-year flood has a 0.02 or 2% chance of being exceeded in any one year.
This extended historical perspective is invaluable in contemporary flood-frequency analysis, significantly amplifying the effective length of the record. The incorporation of historical flood data enhances the analysis, offering a more comprehensive understanding of the dynamics and patterns involved in flooding events. [8]
An intensity-duration-frequency curve (IDF curve) is a mathematical function that relates the intensity of an event (e.g. rainfall) with its duration and frequency of occurrence. [1] Frequency is the inverse of the probability of occurrence. These curves are commonly used in hydrology for flood forecasting and civil engineering for urban ...
The frequency of extremal events, such as severe droughts and storms, often requires the use of distributions that focus on the tail of the distribution, rather than the data nearest the mean. These techniques, collectively known as extreme value analysis, provide a methodology for identifying the likelihood and uncertainty of extreme events.
CumFreq uses the plotting position approach to estimate the cumulative frequency of each of the observed magnitudes in a data series of the variable. [2] The computer program allows determination of the best fitting probability distribution. Alternatively it provides the user with the option to select the probability distribution to be fitted.
However, Wemelsfelder's statistical analysis of water levels measured between 1888 and 1937 at Hoek van Holland enabled the derivation of a probability distribution of storm surges. He published his findings in the Dutch journal de Ingenieur in March 1939, which revolutionised the way flood protection measures were designed in the country. [8] [9]
Flood routing is a procedure to determine the time and magnitude of flow (i.e., the flow hydrograph) at a point on a watercourse from known or assumed hydrographs at one or more points upstream. The procedure is specifically known as Flood routing, if the flow is a flood. [14] [15] After Routing, the peak gets attenuated & a time lag is ...