Flow duration curve
Introduction
The general duration curve is a cumulative frequency curve that indicates the percentage of time during which the measurement of a phenomenon has been equaled or exceeded in a period of time and is used in engineering sciences to make a reasonable estimate of the intensity, duration and frequency of natural phenomena such as rain, wind, sun or flow to which man-made works will be exposed. The diagrams are based on Cumulative Frequency Analysis, which in turn is based on the statistical interpretation of series of measurements made over an extended period of time.
The seasonal variation curve is a way to order, jointly, the result of the general durations of the monthly values of the variable under study.
Events to be classified
In hydrology and meteorology, two types of frequencies are studied:[1].
The differences between the two are:[1].
Elaboration
After obtaining and making the necessary corrections from a series of measurements of the phenomenon, for example the flow of a river (m³/s) in the month of November over 20 years. The diagram of this series of measurements is called a hydrograph.
They are then sorted according to flow in increasing order:.
The range between the minimum flow and the maximum flow is divided into sections of equal duration (in this case 50 m³/s) and the number of times the measurement remains in that range is counted.
Frequency represents the probability of that event occurring.
Seasonal variation curve
To visualize the probabilities of similar events over a range of time, the probabilities of each flow are graphed and the seasonal variation curve is obtained. These curves present various information for the builder of a hydraulic work: