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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.
Frequency analysis [2] is the analysis of how often, or how frequently, an observed phenomenon occurs in a certain range. Frequency analysis applies to a record of length N of observed data X 1, X 2, X 3. . . X N on a variable phenomenon X. The record may be time-dependent (e.g. rainfall measured in one spot) or space-dependent (e.g. crop ...
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.
A 100-year flood is a flood event that has on average a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. [1] A 100-year flood is also referred to as a 1% flood. [2] For coastal or lake flooding, a 100-year flood is generally expressed as a flood elevation or depth, and may include wave effects. For river systems ...
A number of methods can be used to calculate time of concentration, including the Kirpich (1940) [2] and NRCS (1997) [3] methods. Time of concentration is useful in predicting flow rates that would result from hypothetical storms, which are based on statistically derived return periods through IDF curves .
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 ...
Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle.It is one runoff component, the movement of water from the land to waterbodies, the other component being surface runoff.
Scientists and engineers use statistical analysis of streamflow data to determine the likelihood of flood elevations. [11] Theoretically a 100-year flood has a 1 percent chance (1/100 = 0.01 or 1 percent) of occurring in any given year and a 500-year flood has as a 0.2 percent chance (1/500 = 0.002 or 0.2 percent) of occurring in any given year ...