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Open Channel Flow DRAINAGE CRITERIA MANUAL OPEN CHANNEL FLOW CHAPTER 6. OPEN CHANNEL FLOW DESIGN CONTENTS Section Page OC- 1.0 INTRODUCTION .................................................................................................. 1 1.1 Purpose of the Chapter .................................................................................................... 1 1.2 General ............................................................................................................................... 1 1.3 Types of Major Open Channels ....................................................................................... 2 1.4 Issues in Open Channel Planning and Engineering ...................................................... 3 1.5 Fluvial Geomorphology .................................................................................................... 3 1.5.1 Effects of Urbanization on Existing Stream Channels ........................................... 4 1.5.2 Stable Channel Balance ........................................................................................ 4 2.0 OPEN CHANNEL DESIGN PRINCIPLES ............................................................ 5 2.1 General Open Channel Flow Hydraulics ........................................................................ 5 2.1.1 Types of Flow in Open Channels ........................................................................... 5 2.1.2 Roughness Coefficients ......................................................................................... 7 2.1.3 Specific Energy of Channel Flow ........................................................................... 8 2.1.4 Flow Regime .......................................................................................................... 9 2.1.4.1 Critical Flow .......................................................................................... 10 2.1.4.2 Subcritical Flow ..................................................................................... 11 2.1.4.3 Supercritical Flow .................................................................................. 12 2.2 Preliminary Design Criteria ............................................................................................ 13 2.2.1 Design Velocity .................................................................................................... 13 2.2.2 Design Depths...................................................................................................... 13 2.2.3 Design Slopes ...................................................................................................... 14 2.2.3.1 Channel Slope ...................................................................................... 14 2.2.3.2 Side Slopes ........................................................................................... 14 2.2.4 Curvature and Transitions .................................................................................... 14 2.2.5 Design Discharge Freeboard ............................................................................... 15 2.2.6 Erosion Control .................................................................................................... 15 2.2.7 Utility Proximity..................................................................................................... 16 2.3 Choice of Channel Type and Alignment ....................................................................... 16 2.3.1 Types of Channels for Major Drainageways ........................................................ 16 2.3.2 Factors to Consider in Selection of Channel Type and Alignment ...................... 18 2.3.3 Summary of Design Criteria ................................................................................. 19 2.3.4 Environmental Permitting Issues ......................................................................... 24 2.3.5 Maintenance ......................................................................................................... 27 2.4 Design Flows ................................................................................................................... 27 2.5 Maintenance Classification – Primary Channels, Secondary Channels, and Tertiary Channels 28 3.0 OPEN-CHANNEL DESIGN CRITERIA .............................................................. 29 3.1 Grass-Lined Channels .................................................................................................... 29 3.1.1 Design Criteria ..................................................................................................... 30 3.1.1.1 Design Velocity and Froude number .................................................... 30 3.1.1.2 Design Depths ...................................................................................... 30 3.1.1.3 Design Slopes ....................................................................................... 30 3.1.1.4 Curvature .............................................................................................. 30 3.1.1.5 Design Discharge Freeboard ................................................................ 31 3.1.2 Channel Cross Sections ...................................................................................... 31 City of Bella Vista, AR OC-i DRAINAGE CRITERIA MANUAL OPEN CHANNEL FLOW 3.1.2.1 Bottom Width ........................................................................................ 31 3.1.2.2 Trickle and Low-Flow Channels ............................................................ 31 3.1.2.3 Outfalls Into Channel ............................................................................ 32 3.1.3 Roughness Coefficients ....................................................................................... 32 3.1.4 Trickle and Low-Flow Channels ........................................................................... 33 3.1.5 Erosion Control .................................................................................................... 37 3.1.5.1 Erosion at Bends ................................................................................... 38 3.1.5.2 Riprap Lining of Grass-lined Channels ................................................. 38 3.1.6 Water Surface Profile ........................................................................................... 38 3.1.7 Maintenance ......................................................................................................... 39 3.1.8 Calculation Tool ................................................................................................... 39 3.2 Composite Channels ...................................................................................................... 39 3.2.1 Design Criteria ..................................................................................................... 40 3.2.2 Design Procedure ................................................................................................ 40 3.2.3 Water Surface Profile ........................................................................................... 42 3.2.4 Life Expectancy and Maintenance ....................................................................... 43 3.2.5 Calculation Tool ................................................................................................... 44 3.3 Concrete-Lined Channels .............................................................................................. 44 3.3.1 Design Criteria ..................................................................................................... 44 3.3.1.1 Design Velocity and Froude Number .................................................... 44 3.3.1.2 Design Depths ...................................................................................... 45 3.3.1.3 Curvature .............................................................................................. 45 3.3.1.4 Design Discharge Freeboard ................................................................ 45 3.3.2 Concrete Lining Specifications ............................................................................. 46 3.3.2.1 Concrete Lining Section ........................................................................ 46 3.3.2.2 Concrete Joints and Reinforcement ..................................................... 46 3.3.2.3 Concrete Finish ..................................................................................... 47 3.3.2.4 Weep Holes .......................................................................................... 47 3.3.3 Channel Cross Section ........................................................................................ 47 3.3.3.1 Side Slopes ........................................................................................... 47 3.3.3.2 Depth ..................................................................................................... 47 3.3.3.3 Bottom Width ........................................................................................ 48 3.3.3.4 Trickle and Low-Flow Channels ............................................................ 48 3.3.3.5 Outfalls Into Channel ............................................................................ 48 3.3.4 Safety Requirements ........................................................................................... 48 3.3.5 Calculation Tools.................................................................................................. 48 3.3.6 Maintenance ........................................................................................................
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