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<br />Chapter 1 <br />Introduction <br /> <br />1.1. Purpose <br /> <br />This manual presents procedures for the design analysis <br />and criteria of design for improved channels that cany <br />rapid andlor tranquil flows. <br /> <br />1.2. Scope <br /> <br />Procedures are presented without delails of the theory of <br />the hydraulics involved since these details can be found in <br />any of various hydraulic textbooks and publications avail- <br />able to the design engineer. Theories and procedures in <br />design. such as flow in curved channels. flow at bridge <br />piers. flow at cOn!luences. and side drainage inlet struc- <br />tures. that are not covered fully in textbooks are discussed <br />in delail with the aid of Hydraulic Design Criteria (HOC) <br />cham published by the US Army Engineer WaterWays <br />Experiment Station (USAEWES). The charts and other <br />illustrutions are included in Appendix B to aid the desig- <br />ner. References to HOC are by HOC chart number. The <br />use of models to develop and verify design details is <br />discussed briefly. Typical calculations are presented to <br />illustrate the principles of design for channels under vari- <br />ous conditions of flow. Electronic computer program- <br />ming techniques are not treated in this manual. However. <br />most of the basic hydraulics presented herein can be <br />adapted for computer use as illustrated in Appendix D. <br /> <br />1-3. References <br /> <br />References are listed in Appendix A. <br /> <br />1-4. Explanation of Tenns <br /> <br />Abbreviations used in this manual are explained in the <br />Notation (Appendix n. The symbols employed herein <br />confonn to the American Standard Letter Symbols for <br />Hydraulics (American Society of Mechanical Engineers <br />1958) with only minor exceptions. <br /> <br />1.5. Channel ClassifIcation <br /> <br />In this manual. flood control channels are considered <br />under two bro:Jd classifications: rapid- and tranquil-flow <br />channels. The most imponant ch=teristics that apply to <br />rapid and tranquil flows are listed below: <br /> <br />a, Velocities, Rapid flows have supercritical veloci <br />ties with Froude numbers gre:uer than I (F > I). and <br /> <br />EM 1110-2-1601 <br />1 Jul 91 <br /> <br />tranquil flows have subcritical velocities with Froude <br />numbers less than I (F < I). <br /> <br />b, Slopes, Inven slopes in general are greater than <br />critical slopes (So> Sc) for rapid flow and less than criti, <br />cal slopes (So < Sc) for tranquil flow, <br /> <br />c. Channel storage, Channel storage is usually <br />negligible in rapid flow. where:ls it may be appreciable in <br />natural rivers with tranquil flow. <br /> <br />d. Discharge. All discharges are nonnally confined <br />within the channel for rapid flow (no overbank flow). <br /> <br />Other char:1cteristics such as standing waves. surges. and <br />bed configuration that differ under the influence of rapid- <br />or tranquil-flow conditions should be recognized and <br />considered as the occasion demands. Rapid and tranquil <br />flows can occur within a longitudinal reach of a channel <br />with changes in discharge. roughness. cross section. or <br />slope. Channel improvements may bring about changes in <br />flow characteristics. <br /> <br />1-6. Preliminary InvestigatIons for SelectIon of <br />Type of Improvement <br /> <br />The investigation required in selecting the type of channel <br />improvement to be adopted involves three considemtions: <br />physical features of the area. hydraulic and hydrologic <br />aspects. and economy. <br /> <br />a, Phvsical features. The topography of the = <br />controls in' a general way the channel alignment and <br />invert grades. Of prime importance. also. are width of <br />available right-of-way: location of existing channel: and <br />adjacent existing strUClllreS. such as bridges. buildings. <br />transportation facilities. utility strUCtures. and outlets for <br />local dr:tinaee and tributaries. Inven slopes may be con- <br />trolled by elevations of existing structures as well as by <br />general topography. elevations at ends of improvements, <br />and hydraulic fe:ltures. <br /> <br />b, Historical and observed elements. The flow char- <br />acteristics noted in historical records and indicated from <br />delailed observation of existing conditions will usually be <br />basic to the selection of type of improvement or design. <br />With the flood discharges detennined. the interdependent <br />factors that detennine improvement methods and general <br />channel alignment are slope of inven, width and depth of <br />flow rou ehness coefficient. the presence or narure of <br />ag~io~ and degradation processes. debris tr:lnspona- <br />tion. bank erosion, cutoffs, and bar fonnations. <br /> <br />1-1 <br /> <br />~--- <br />