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

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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