1 / 18

Aims today: To learn about: Channel Efficiency The Hydraulic Radius The Graded Profile

Aims today: To learn about: Channel Efficiency The Hydraulic Radius The Graded Profile X-Sections along a long profile Exam Style Questions. 1 Minute a Mark. 8 marks. 8 minutes http://www.youtube.com/watch?v=vKj8VLHpUI4. A. Stream Channels (Recap). B. Water flow in rivers.

porter-barrera
Download Presentation

Aims today: To learn about: Channel Efficiency The Hydraulic Radius The Graded Profile

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Aims today: • To learn about: • Channel Efficiency • The Hydraulic Radius • The Graded Profile • X-Sections along a long profile • Exam Style Questions

  2. 1 Minute a Mark • 8 marks. 8 minutes http://www.youtube.com/watch?v=vKj8VLHpUI4

  3. A. Stream Channels (Recap)

  4. B. Water flow in rivers • The energy of a river is determined by: • Friction • The slope of the channel • The discharge • The size of the channel

  5. Don’t forget: Paddling explanations…rapids, pool Laminar Flow Turbulent Flow Water particles move in erratic paths down-stream, criss-crossing and mixing with other particles. Results in much more erosion and is capable of keeping particles suspended for longer periods of time. • Occurs when water particles move in sheets parallel to the channel bed, flowing slowly in a smooth and shallow channel. • Full laminar flow is rare.

  6. Don’t forget: Manning’s Coefficient Video Where art thou fastest flow?

  7. Where art thou fastest flow? When people compare the rushing water in the small channel of stream near its source, with the apparent sluggishness of water downstream, they often conclude that water flows more quickly near the source. This was shown to be wrong as a result of the work done in 1891 by the Irish engineer, Robert Manning, who attempted to quantify the roughness of stream beds. Manning developed his roughness coefficient into an equation that described the velocity of flow.

  8. Velocity: the greatest velocity is where friction is least i.e. away from banks, bed and air. The velocity is slowed at the surface due to air (wind resistance).The shape of the cross-section controls the point of maximum velocity in a river’s channel. Straight Channel Meandering Channel An asymmetrical channel carries faster-moving water towards the outside of a bend. • Symmetrical channel • Fastest flow in the centre slightly below the surface.

  9. 1. CHANNEL EFFICIENCY Measure of the ability of a river channel to move water and sediment. The most efficient channels are generally semicircular in cross-section, and it is this shape that water engineers try to create when altering a river channel to reduce the risk of flooding.

  10. 2. THE HYDRAULIC RADIUS The hydraulic radius is a measure of a river's channel efficiency, and is used by water engineers to assess the likelihood of flooding. The hydraulic radius of a channel is defined as the ratio of its cross-sectional area to its wetted perimeter. The greater the hydraulic radius, the greater the efficiency of the channel and the less likely the river is to flood. The highest values occur when channels are deep, narrow, and semi-circular in shape.

  11. 3. THE GRADED PROFILE

  12. 4. X-SECTIONS OF A LONG PROFILE

  13. Contrast the channel shapes and comment on the relative efficiency of the two river cross sections ( 7 marks)

More Related