Chapter 7: ChannelsAnchor: #i1016972
Section 1: IntroductionAnchor: #i1016977
Open Channel Types
In this chapter, the term open channel includes the total conveyance facility (the floodplain and stream channel). This chapter addresses required design criteria, design philosophy, and channel design and analysis procedures.
The various types of open channels include stream channels, roadside channels or ditches, and artificial channels such as irrigation channels or drainage ditches. The hydraulic design process for open channels consists of establishing criteria, developing and evaluating alternatives, and selecting the alternative that best satisfies the criteria. Plan for capital investment and probable future costs, including maintenance and flood damage to property, traffic service requirements, and stream and floodplain environment. Evaluate risks warranted by flood hazard at the site, economics, and current engineering practices.
Use channel design to determine the channel cross section required to accommodate a given discharge. This includes sizing outfall channels and various roadway ditches. Channel design involves selection of trial channel characteristics, application of channel analysis methods, and then iteration until the trial characteristics meet the desired criteria.
Analyze the channel to determine the depth and average velocity at which the discharge flows in a channel with an established cross section. Use channel analysis most frequently to establish a water surface elevation that influences the design or analysis of a hydraulic structure or an adjacent roadway profile scheme.
Assess the following when designing transportation drainage systems:
- Anchor: #NIOIEKJE
- potential flooding caused by changes in water surface profiles Anchor: #GUHGKLHM
- disturbance of the river system upstream or downstream of the highway right-of-way Anchor: #LLJHEHGL
- changes in lateral flow distributions Anchor: #MPMHGMEH
- changes in velocity or direction of flow Anchor: #MGREHLEN
- need for conveyance and disposal of excess runoff Anchor: #FMNJLHGL
- need for channel linings to prevent erosion.
Methods Used for Depth of Flow Calculations
Use the Slope Conveyance Method and Standard Step Backwater Method), described in this chapter, for calculating depth of flow for analyzing an existing channel or for designing a new or improved channel.