Some Basic Aspects of CHANNEL HYDRAULICS - PowerPoint PPT Presentation

Loading...

PPT – Some Basic Aspects of CHANNEL HYDRAULICS PowerPoint presentation | free to download - id: ef53d-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Some Basic Aspects of CHANNEL HYDRAULICS

Description:

The volume of water that passes by any given point along a ... these man-made channels can aggrade and fill with sediment, diminishing their design capacity ... – PowerPoint PPT presentation

Number of Views:44
Avg rating:3.0/5.0
Slides: 14
Provided by: cwat9
Learn more at: http://web.mst.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Some Basic Aspects of CHANNEL HYDRAULICS


1
Part 2
  • Some Basic Aspects of CHANNEL HYDRAULICS

2
  • The volume of water that passes by any given
    point along a watercourse is called Q, for
    quantity of flow. It is generally expressed in
    units of cubic feet per second (cfs) or cubic
    meters per second (m3/s).

3
MANNINGS EQUATION for Open Channel Flow (1889)
  • Where
  •           Q Flow Rate, (ft3/s)
  •           v Velocity, (ft/s)               
  •           A Flow Area, (ft2)
  •           n Mannings Roughness Coefficient
  •           R Hydraulic Radius, (ft)
  •           S Channel Slope, (ft/ft)

4
Hydraulic Depth and Radius
  • In terms of frictional head losses, the perimeter
    is important. Hydraulic radius, Rh, is defined as
    the area of the flow section divided by the
    wetted perimeter, Pw, which is shown on the
    figure at left and is written as Rh A/Pw

5
Mannings n for natural channels
  • For main channels with clean, straight, full
    stage, no rifts or deep pools navg .030
  • For mountain streams with channel bed of gravels,
    cobbles, and few boulders navg .040
  • For flood plains with scattered brush, heavy
    weeds, navg .050
  • For excavated earthen channel, clean and recently
    completed navg .018

6
  • Trapezoidal channels are commonly excavated for
    flood control because they have predictable
    characteristics
  • Over time, these man-made channels can aggrade
    and fill with sediment, diminishing their design
    capacity

7
  • Flow data is measured at discrete points along a
    watercourse, known as gaging stations. Velocity
    data is usually measured during high flows on
    stage recorders, like that shown at right. These
    data are compiled to create statistical databases
    on runoff and channel flow.

8
Flow Data
  • Gauging stations usually record data on channel
    width, depth and velocity during various flow
    stages
  • These data can be used to calculate the quantity
    of flow, Q
  • If sufficient data exists, a stage record can be
    constructed for this site which relates Q to flow
    velocity, depth, and width

9
  • The hydrograph is a graphical plot of Q versus
    time at a given point along the stream or river.
    It is influenced by a number of factors,
    including interflow.

10
Impacts of Land Use and Impermeable Surfaces
  • Changes in land use and vegetation affect runoff
    by increasing the peak flow, causing erosion of
    bed and banks
  • Hard, impermeable surfaces such as pavement and
    roofs tend to reduce the time to concentration

11
Runoff Coefficients
  • The runoff coefficient depends on ground cover,
    land use, and antecedent moisture
  • The time-to-concentration depends on slope,
    permeability of the ground surface, and distance
    to an adjacent watercourse

Terrasets caused by compaction of grazing cattle
hooves
Slopes cleared of vegetation for grazing
12
Lag Time
  • Lag time describes the time interval between the
    center of mass of rainfall and the runoff
  • The lag time diminishes with increasing
    impermeable surfaces

13
  • The lag time describes the interval between the
    centroid of the precipitation and the centroid of
    flow in the hydrograph
About PowerShow.com