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<br />
<br />2
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<br />PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS
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<br />it is believed that the principles established may be
<br />applicable to humid regions as well.
<br />Pract.ical considerations, along with personal bent,
<br />dictated that channels of arid rather than humid regions
<br />should receive our attention first. "Accelerated ero-
<br />sion" in the West is a problem of great social and eco-
<br />nomic importance. The arroyos that trenched alluvial
<br />valleys of the Southwest beginning in the latter part of
<br />the 19th century, some of which even now are eroding
<br />apace, are spectacular examples of ephemeral streams.
<br />Conservationists, range managers, geologists, and a host
<br />of others have debated the cause of gullying, have
<br />experimented with methods of gully control, and have
<br />tried to prognosticate the eventual status of the channel
<br />system. But in all such efforts practically no attempt
<br />has been made to study the process of gully erosion
<br />itself, to describe the hydraulic conditions in the eroding
<br />cliannels, or to understand the nature of the equilibrium
<br />which was upset by grazing and climatic change. It
<br />seems bootless to spend large sums on the control of
<br />gullies and arroyos without concomitant attempts to
<br />increase knowledge of their hydraulic characteristics.
<br />The present study provides new data that are perti-
<br />nent to a fuller understanding of ephemeral streams.
<br />Specifically, geometric and hydraulic properties of
<br />channels are related to the drainage-net configuration.
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<br />NEW MEXICO
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<br />The plan of presentation is as follows: First, the chan-
<br />nels in the area studied are described and the methods
<br />of investigation outlined. Next, the measurements of
<br />hydraulic variables, including channel shape, discharge,
<br />and sediment load are presented. A method of inte-
<br />grating hydraulic characteristics with properties of the
<br />drainage net is shown to increase markcdly the utility
<br />of available data, Finally, the role of equilibrium in
<br />ephemeral channels, as related to the accelerated erosion
<br />problem, is discussed.
<br />Many colleagues and friends gave us continuing
<br />advice and assistance in the study, and particular
<br />thanks are due M. Gordon Wolman, Thomas Maddock,
<br />Jr., John T. Hack, and Walter B. Langbein. The
<br />field work was made considerably easier in many waYfI .
<br />by the cooperation of Paul C. Benedict and Berkeley
<br />Johnson. Charlcs E. Stearns visited us in the field
<br />and later discussed the manuscript with us.
<br />Weare indebted to John T. Hack and Stanley
<br />Schumm for permission t,o include in this report some
<br />of their unpublished data.
<br />
<br />GEOGRAPHIC SETTING AND BASIC MEASUREMENTS
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<br />Nearly all the data included in this report were col-
<br />lected in the basins of the Rio Galisteo and Rio Santa
<br />Fe, tributaries to the Rio Grande in semiarid central
<br />New.\lexico (see fig. 1),
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<br />FIGURE I.-Location map showing area In New Mexico where detailed studies were made.
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