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<br />SUMMARY
<br />
<br />Daryl B. Simons
<br />Director, Engineering Research Center; Professor, Civil
<br />Engineering, Colorado State University,
<br />Fort Collins, Colorado, U.S.A.
<br />
<br />INTRODUCTION
<br />
<br />Alluvial river systems such_as the three examined in this wo~kshop
<br />are very dynamic in nature and generally experience significant changes
<br />in depth, width, alignment, and stability with time. A systematic
<br />analysis is required to distinguish between changes due to the natural
<br />dynamic characteristics of the system and those due to man's activities.
<br />The changes may be defined a~ degradation, aggradation, and lateral
<br />migration. Degradation and lateral migration can endanger adjacent
<br />property, bridges, and other hydraulic structures while aggradation can
<br />reduce channel capacity, increase lateral erosion, and increase the
<br />flooding potential.
<br />
<br />The dynami c nature of ri ver and watershed systems requi res that
<br />local problems and their solutions be considered in terms of the entire
<br />system. Natural and man-induced changes in a river frequently initiate
<br />responses that can be propagated for long di stances both upstream and
<br />downstream (Simons and Senturk 1977). Successful river util i zat i on and
<br />water resources development require a general knowledge of the entire
<br />watershed and river system and the processes affecting it. This goal
<br />can be achieved only through a basic understanding and application of
<br />physical processes governing channel response and the utilization of
<br />physical and numerical techniques.
<br />
<br />..-----
<br />
<br />In the past the emphasis of research and ana lys is has been on
<br />rivers with fine-grained alluvial beds and it is only recently that
<br />attention has been focused on flow in gravel-bed channels such as the
<br />Yampa River and Poplar Creek. In recent decades, though. increasing
<br />human involvement with upland and mountain regions. activities such as
<br />-agri cu1 ture, forestry. recreation, gravel mi ni ng, reservoi r construc-
<br />tion, river regulation. and highway construction have affected the
<br />gravel-bed river environment. Gravel-bed rivers have therefore increas-
<br />ingly felt the impact of human activities and have themselves become the
<br />focus of engineering projects. As a result. there is an urgent need for
<br />the development of dynamic modeling techniques that can be applied to
<br />the management of gravel-bed rivers.
<br />
<br />Thi s summary is intended to hi gh 1 i ght the major themes of the
<br />participants' papers regarding the scope, approaches, and data require-
<br />ments for analyzing the general question of downstream river channel
<br />changes associated with diversions or reservoir construction. The
<br />summary will also relate these major themes to the instream aquatic
<br />habitat, a task not specifically assigned to the participants in their
<br />analysis. A careful reading of the papers which follow will reveal
<br />striking consistencies in these areas as well as several interesting
<br />digressions from what can be considered the usual thrust of river system
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