Beaver Creek Corridor Design and Analysis By: Alex Previte
Overview Introduction Key concepts Model Development Design Accuracy Conclusion
Refresh v = Beaver Creek Site = Wittenberg
Introduction Low head dam : small overflow dam used to alter the flow characteristics of a river or stream Dangers: Drowning Alter Ecosystem User Friendly: Kayaking
Introduction HEC-RAS Hydrologic Engineering Centers River Analysis System Computer program Used for analyzing rivers and streams Able to compute flow characteristics given certain parameters
Profile Plot Geometry profile Data taken over 300 Ft (horizontally) Contain contour of stream at vertical location Cross-sections River stations Contain Profile information (Geometry) Tracks distance (Upstream to downstream) 0 ft. 3 2 1 300 ft.
Elevation (ft) Cross-Section Beaver_Creek Plan: Imported Plan 01 01/21/2013 11 965.0001.028 Legend 960 955 950 EG PF 1 WS PF 1 Crit PF 1 Ground Bank Sta 945 0 50 100 150 200 250 300 Station (f t) X-axis = Horizontal width of River Station Y-axis = Elevation above sea level = Bank Station marker Contour = shape of creek bed at that station Stage Height (Y) = Distance from channel bottom to surface
Elevation (ft) Energy Equation Z 965 960 955 950 Beaver_Creek Plan: Imported Plan 01 01/21/2013 11.0001.028 V 945 0 50 100 150 200 250 300 Station (f t) Y g Legend EG PF 1 WS PF 1 Crit PF 1 Ground Bank Sta a 1, a 2 = Velocity weighting coefficients (error in average velocity) h e = Energy head loss
Development Determine and adjust Manning n value River bank adjustment One low-head dam replaced by a single v-notch drop structure Hydraulic Jump Subcritical to supercritical
Elevation (ft) Manning Equation 962 Beaver_Creek Plan: Imported Plan 02 05/05/2013 1.04.028.04 Legend 960 EG PF 1 958 956 V = A WS PF 1 Crit PF 1 Ground Bank Sta 954 952 0 50 100 150 200 250 300 Station (f t) Equation: Q = VA = 1.00 n AR 2 3 s n = Manning s Roughness Coefficient R = Hydraulic Radius, (m) S = Channel Slope, (m/m)
Manning N Similar to coefficient of friction Shows the resistance to fluid flow Higher n means more resistant to flow
Froude Number Froude Number U = Velocity of flow g = Acceleration of gravity h = Depth of flow relative to the channel bottom = Wave velocity Unitless gh U
Supercritical and Subcritical Flow Is the Froude number > or < than 1? Fr>1 = Supercritical Fr<1 = Subcritical Supercritical When flow velocity is greater than wave velocity Subcritical When flow velocity is less than wave velocity Hydraulic Jump Occurs when a flow at high velocity discharges into a zone that can't sustain that high wave velocity.
Sub or Supercritical Flow gh U Subcritical Flow gh U Supercritical Flow
Hydraulic Jumps With V-notch want to create a hydraulic jump
Designing V-notch Flow = subcritical supercritical subcritical Upstream from dam is already subcritical flow Froude Number Greater flow velocity, U, results in supercritical flow Manning Equation Q = VA = 1.00 AR 2 3 s n Q is constant, decreasing A, increases V
Elevation (ft) Designing V-notch Flow Prior to dam is subcritical Fr<1 Supercritical flow over the dam Fr>1 Not safely passable by kayak or canoe 944 0 200 400 600 800 1000 954 952 950 948 946 Beaver_Creek Plan: Imported Plan 01 04/26/2013 RIVER-1 Reach-1 Main Channel Distance (ft) Legend EG PF 12 WS PF 12 Crit PF 12 Ground
Elevation (ft) Elevation (ft) Designing V-notch 964 962 Original channel shape at the dam site Beaver_Creek Plan: Imported Plan 02 05/03/2013 2.04.028.04 Legend EG PF 5 Redesigned V-notch Decrease area, increase velocity of flow Beaver_Creek Plan: Imported Plan 02 04/30/2013 960 958 WS PF 5 Ground 960.04.028.04 Legend 956 954 952 950 0 50 100 150 200 250 300 Bank Sta 958 956 954 EG PF 12 Crit PF 12 WS PF 12 Ground Bank Sta Station (f t) 952 950 0 50 100 150 200 250 300 Station (f t)
Elevation (ft) Elevation (ft) Hydraulic Jump Constant Q (93 cfs) Beaver_Creek Plan: Imported Plan 02 04/30/2013.04.028.04 960 Legend Stage height of crosssection following V- notch is 1.94 ft. 958 956 954 EG PF 12 Crit PF 12 WS PF 12 Ground Bank Sta 960 958 Beaver_Creek Plan: Imported Plan 02 04/30/2013 8.04.028.04 Legend EG PF 12 952 950 0 50 100 150 200 250 300 Station (f t) 956 954 952 WS PF 12 Crit PF 12 Ground Bank Sta Stage height at V- notch is 1.43 ft. 950 948 0 50 100 150 200 250 300 Station (f t) Hydraulic Jump?
Hydraulic Jump Ratio of height y 2 y 1 = 1.36 y 1 is the stage height of the v-notch y 2 is the stage height of the following cross-section Success! Created an undulant jump or rapid which is passable by both canoe and kayak
Hydraulic Jump Is the model consistent? Q (cfs) A (ft 2 ) V (f/s) gh Fr V-notch 93 18.83 4.94 3.75 1.32 post V 93 163.18 0.57 4.36 0.13 Fr 1 = 1.32 > 1, Fr 2 = 0.13 < 1 Supercritical to subcritical flow Indeed our structure has a Hydraulic jump
Model Accuracy Is stage height unreasonably high? Uncharacteristic flow can damage downstream structure of bed Must be consistent with the stage discharge of previous structure Offset rating curves for comparison
Stage (Ft) Stage (Ft) Stage-Discharge Curve Pre Modification Post Modification Stage-Discharge RS 11 1.4 Stage-Discharge RS11 1.2 1.5 1.0 1.0 0.5 0.8 0.6 0.4 0.2 0.0 0.0 0 20 40 Dishcarge (cfs) 60 80 0 20 40 Discharge (cfs) 60 80 Dam is located at RS 11 Similar shape indicates similar behavior Reasonable stage height in modification Indicates that if these structural changes are implemented, the creek will resume its normal flow downstream of modification Roughly a 2.5 inch decrease in stage height
Conclusion HEC-RAS modeling to create modification to creek Model was consistent Dam modifications are possible
Acknowledgements Dr. George Dr. Williams
Questions?