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Show DEFINITION AND GENERAL DESCRIPTION 27 commented on the looseness and inaccuracy of using the terms as though they were synonymous, for they do not have the same meaning. While there cannot be a running stream without a watercourse, said the court, nothing is more common than a watercourse without a stream. It is true that in strict legal parlance a stream of water is not a watercourse-it is assuredly one of the essential elements of an overall natural system called a watercourse, but only one of them. When exact terminology is required in this book, the term watercourse is used to designate this overall system of which the stream is only a part. Otherwise, to avoid montonous repetition, such terms as stream, creek, river, tributary, etc., may be used when appropriate. The Surface Stream System The concept of a surface stream system has long been recognized in discussions of the right to make use of the water of surface watercourses. The stream system consists of the main channel and of all tributary channels through which water naturally flows by gravity into the main channel. It comprises a main watercourse and a number of tributary watercourses of varying size. This concept is particularly important in the determination of rights to the use of water in the arid and semiarid West-not only rights of prior appropriation and beneficial use, but riparian rights as well. The use of water under the appropriation doctrine is not confined to lands contiguous to the stream channels, for the doctrine-subject to priorities of right-sanctions the diversion of waters from main streams and from their tributaries, flowing through either agricultural or nonagricultural country, and conveyance of the diverted water to areas from which there will be no natural return to the main channel. The prior appropriator is protected by law against diversions from upstream tributaries under junior rights which would materially interfere with the exercise of his own prior rights. Likewise, in the jurisdictions in which the riparian doctrine is substantially recognized, upstream diversions either from the main stream or from tributaries may be restricted-or, indeed, completely stopped-to the extent that they interfere with the rights of downstream riparian owners. Gains and Losses of Water Surface watercourses are fed by the flow in tributary channels, by diffused surface water flowing over the banks of the stream, by waste water discharged into the channel, and by ground water seeping into the channel through its banks and bed. The tributary sources of supply may be natural sources alto- gether, such as rains and melting snows, or they may, and in the irrigated areas usually do, include waste and seepage waters or return flow from irrigated lands. The sides and bottom of the channel may be impervious in some places and not in others; where not impervious, the soil across and through which the |