1. Open Channel Hydraulics Specific Energy & Discharge Control Structures Environmental Hydrology Lecture 13

2. Potential and Kinetic Energy in Open Channels Total head (H) = Z + P/  + v 2 /2g Bernoulli equation Elevation above datum Pressure of fluid column (P =  gy =  y) Velocity head y1y1 y2y2 Z=0 (datum) V 1 2 / 2g V 2 2 / 2g Z1Z1 Z2Z2 H1H1 Water surface energy grade line

3. Specific Energy See also Ward & Trimble, Fig 8.1 Specific energy (E) = y + v 2 /2g

4. Froude Number Fr = v √g y where: V = average velocity g = acceleration due to gravity (9.81m/sec 2, 32.2 ft/sec 2 ) y = flow depth Fr < 1 subcritical flow Fr = 1 critical flow Fr > supercritical flow

5. Specific Energy See also Ward & Trimble, Fig 8.1 Specific energy (E) = y + v 2 /2g

6. “Meatgrinder” – So. Fork American River Image source: Greg Pasternack, UC Davis Hydraulic Jump

7. Image Source: http://einstein.atmos.colostate.edu/~mcnoldy/HydraulicJump.htmhttp://einstein.atmos.colostate.edu/~mcnoldy/HydraulicJump.htm l

8. Measuring Discharge Images: U.S. Geological Survey

9. Discharge Control Structures V-notch weirParshall flume

10. Discharge Control Structures

11. Stilling well Weir or Flume

12. Weir equations Ward & Trimble, Figure 8.6 Q = CLH 3/2 where C is a weir coefficient; other terms defined in illustration. Note: weir and flume equations vary by structure design! See: http://www.lmnoeng.com/Weirs/RectangularWeir.htmhttp://www.lmnoeng.com/Weirs/RectangularWeir.htm