1 / 19

Hydraulic Structures for Discharge Measurement

Hydraulic Structures for Discharge Measurement. Flow Measurement. Measurement Approaches. Direct methods (stream gaging) Current-meter method Floats Tracer-dilution technique Ultrasonic method Electromagnetic method. Measurement Approaches. Hydraulic Devices Weirs and notches Orifices

slade
Télécharger la présentation

Hydraulic Structures for Discharge Measurement

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. Hydraulic Structures for Discharge Measurement

  2. Flow Measurement

  3. Measurement Approaches • Direct methods (stream gaging) • Current-meter method • Floats • Tracer-dilution technique • Ultrasonic method • Electromagnetic method

  4. Measurement Approaches • Hydraulic Devices • Weirs and notches • Orifices • Flumes • Indirect Techniques • Slope-area method • Rating Curve

  5. Definition of Terms • Stage: Height of water surface above a fixed datum • Rating: Relationship between stream stage and discharge • Control: Feature that results in a one-to-one relationship between stage and discharge

  6. Measuring Velocity • Current meters • Cup-type (Price and pygmy) • Propeller type • Inductance V = a + bN where V = flow velocity; a = starting velocity to overcome mechanical friction; b = equipment calibration constant; N = revolutions/sec

  7. Current Meters

  8. Measuring Velocity • Pitot Tubes: Suitable only for clean water • Floats: Suitable for straight channel, V = L/T • .

  9. Velocity Distributions

  10. Vertical Velocity Distribution

  11. Depth < 0.6m ; 0.6 water depth from the water surface = V V 0.6d + V V 0.2d 0.8d = £ £ V 0.6m Depth 2m 2 + + V 2V V 0.2d 0.6d 0.8d = ³ V Depth 2m 4 Mean Flow Velocity Estimation • Mean Velocity

  12. Mean-section Method

  13. Mid-section Method

  14. Stage-Discharge Ratings • If it is not possible to install a weir or flume (large channel), need to develop a stage-discharge rating • 3 basic types • Simple stage-discharge • Control produces one-to-one rating • Slope-stage-discharge • Velocity-stage-discharge

  15. Stream Gauges

  16. Storage Hysterisis • In natural rivers, the H-Q relationship in general appears to be a loop, rather than single-valued.

  17. Simple Rating • In general, ratings in natural channels follow a logarithmic shape (power function) • Rating has an offset at the “point of zero flow” • The point of zero flow can be determined graphically

  18. Use of Manning Equation • Stage is also related to the outflow via a relationship such as Manning's equation

  19. By Manning formula: 1 1 æ ö h 2 2 L = = Q K S K ç ÷ f è L ø where 1 2 = ´ K (K K ) 1 2 2 1 3 = = K A R , i 1, 2 i i i n i ¹ K K if flow cross - section is not uniform, minor loss should 1 2 be subtracted from h L. Measurement of Stream Flow (d) Area-Slope Method

More Related