Front cover: On the left, photograph of a USGS hydrographer making a FlowTracker acoustic Doppler velocimeter discharge measurement at Little Eagle Creek at Speedway, Ind. (USGS station no. 03353600); on the right, photograph of a USGS hydrographer making a tethered boat acoustic Doppler current profiler discharge measurement from a cableway at the Snake River near Moran, Wyo. (USGS station no. 13011000). Back cover: In the background, 1890 black and white photograph of USGS hydrographers making a mechanical current meter discharge measurement from a cableway at the Arkansas River near Canyon City, Colo. (USGS station no. 07096000); and on the right, 1958 black and white photograph of a USGS hydrographer making a mechanical current meter discharge measurement at the Cedar River at Belgrade, Nev. (USGS station no. 06791800). For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod. Discharge Measurements at Gaging StationsTo order this and other USGS information products, visit

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This series of manuals on Techniques and Methods (TM) describes approved scientific and data-collection procedures and standard methods for planning and executing studies and laboratory analyses. The material is grouped under major subject headings called "books" and further subdivided into sections and chapters. Section A of book 3 is on surface-water techniques. The unit of publication, the chapter, is limited to a narrow field of subject matter. These publications are subject to revision because of experience in use or because of advancement in knowledge, techniques, or equipment, and this format permits flexibility in revision and publication as the need arises. Chapter A7 of book 3 (TM 3-A7) deals with stage measurement at gaging stations. The original version of this chapter was published in 1968 as U.S. Geological Survey (USGS) Techniques for Water-Resources Investigations, chapter A7 of book 3. New and improved equipment, as well as some procedural changes, have resulted in this revised second edition of "Stage measurement at gaging stations." This edition supersedes USGS Techniques of Water-Resources Investigations 3A-7, 1968, "Stage measurement at gaging stations," by T.J. Buchanan and W.

The convolution integral is used to compute continuous variations in channel loss and base flow that result from a reservoir release on the North Canadian River in central Oklahoma. The open channel flow hydrograph is routed by using the unit response method and then modified for interaction with the aquifer. Stream losses and gains are evaluated from the arbitrary fluctuations in stream stage by using average values of aquifer parameters. In spite of gross simplification pertaining to the nature of the groundwater system, good agreement with the actual flow hydrograph is obtained.

The Clark Method, modified slightly, was used to develop a synthetic, dimensionless hydrograph that can be used to estimate flood hydrographs for ungaged urban watersheds. Application of the technique results in a typical (average) flood hydrograph for a given peak discharge. Input necessary to apply the technique is an estimate of basin lag time and the recurrence interval peak discharge. Equations for this purpose were obtained from a recent nationwide study on flood frequency in urban watersheds. A regression equation was developed which relates flood volumes to drainage area size, basin lag time, and peak discharge. This equation is useful where storage of floodwater may be a part of design or flood prevention.