Reliable estimates of streamflow characteristics are needed for planning, design, and operation of works for providing water supplies and for protection from flooding. This book brings together some of the most useful estimation methods - those that are simple, practical, and require only commonly available or readily obtainable data, and which give results comparable in accuracy with those derived from more sophisticated methods. The author describes how streamflow data are collected, how the characteristics are computed, how they are changed by man's activities, and how they are used in planning and design. Chapters describing statistical principles and techniques, and the effects of various climatic and physiographic factors on streamflow are included. The analytical methods are described in sufficient detail that the reader can apply them to his data. Further applications and other techniques are referred to in bibliographies.

Once-monthly streamflow measurements were used to estimate long-term mean annual flow, mean monthly flow, and various points on the flow-duration curve for 72 sites in the mountainous areas of western Montana. The estimated flow characteristics at 56 measurement sites, together with data from 22 gaging stations, were used to develop maps showing the variability of mean annual runoff, in inches, for three areas.