SCOURING VELOCITY OUT OF WATERWAY DESIGN TIME TO CLEAN-UP DESIGN GUIDELINES STORMWATER 2018 RICK DENNIS ?
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S C O U R I N G V E L O C I T Y O U T
O F W A T E R W A Y D E S I G NT I M E T O C L E A N - U P D E S I G N G U I D E L I N E S
STORMWATER 2018
R I C K D E N N I S
?
WAT ERWAY S COUR
• Direct result of hydrodynamic forces - shear stress 𝜏
• Extensive scientific literature but practitioners still commonly adopt velocity based approaches
• Development codes – no-worsening
𝜏 = 𝜌gyS 𝜏 =𝜌g𝑉2𝑛2
𝑦 ൗ1 3
P ROF ILE
• Uniform channels:• Max V near surface
• Max 𝜏 bed
• Areas of high velocity / low shear stress
• Natural channels – turbulence, rough bed forms, variable cross sections, meanders etc.
H Y D RAULIC MOD ELS
• 2D models output shear stress directly
• Replace velocity with shear stress criteria?
• Hydro-morphologic?
• Suitable case study?
TC D EB B IE
Nearmap Pre
< US Dam 1km DS Gauge 4km >
Nearmap Post
< US Dam 1km DS Gauge 4km >
• TUFLOW HPC (2018-03-AB) using ALS (pre-event) bathy
• Observed gauge data upstream boundary
• WBNM (2012) hydrology local inflows
T UF LOW
TF Max V
TF Max BSS
TF Peak BSS
TF Peak BSS Uniform n
D ELF T 3D
• Creation of a morphologic model Delft3d FM 2018-03
• Validated static-bed case to Tuflow
• Simple morph parameters:• Uniform, single layer
• Van Rijn 1993
D3D Peak BSS Static
TF Peak BSS
D ELF T 3D
D3D Bathy Pre
D3D Bathy Post
D3D Bathy Diff
D3D Peak BSS Morph
TF Peak BSS
CO NC LUS IO NS
• Consistent BSS upstream = bed replacement*
• High BSS magnitude gradients = problem areas
• Static bed models can be effective tools – be aware of roughness transitions, low depths, structure links etc.
• Manual inspection vs. auto grid processing?
• Impact assessments – BSS difference mapping?
• Quantify these areas by simple metrics? Guidelines?
R I C K . D E N N I S @ A L L A N D E N N I S . C O M . A U
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