Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Civil Engineering


Various graphical methods have been developed to handle the statistical data gathered for hydrological studies. Those most familiar are probably the hydrograph, the mass curve, and the flow-duration curve. The first two graphical techniques have been in use for numerous years and as a result, are described in many textbooks. The first published writings dealing with the flow-duration curve are believed to have been released in about 1878. However, the general use of the flow-duration curve started around the year 1915, but as late as 1934 it was felt that many of the fundamental principles of the flow-duration curve were not fully understood by many engineers. Flow-duration curves and tables are statistical devices which show the probability of occurrence of different flows. In actuality, the flow-duration curve or table gives the percentage of time a certain flow is equaled or exceeded. A further discussion on the definition, construction, and uses of the flow-duration table and curve will be presented later in this paper. A series of studies on the seasonal flow characteristics of various river basins in eastern South Dakota have been conducted at South Dakota State University. During the course of these studies of the seasonal variations in stream flow, conducted by Rakness and Chen. It was considered useful to construct the flow-duration curves for the streams being studied. It was shown by Rakness that an annual flow-duration curve or table will not depict the seasonal variations of a stream. That is to say, while a given flow may be equaled or exceeded 50% of the time, the annual flow-duration curve does not indicate when the flow is available. For example, the time when the flow is available is extremely important in the case of irrigation, water supply, fish life propagation, pollution control, or for any other usage where the demand is seasonal. As a result of these studies and the apparent utility of the seasonal flow-duration table, it became apparent that a computer program capable of constructing the seasonal flow-duration table directly from the given records would be an important tool for hydrological studies. This awareness of the need for a computer program to construct the seasonal flow-duration table resulted in the study described in this paper.

Library of Congress Subject Headings


Programming languages (Electronic computers)



Number of Pages



South Dakota State University