intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 
 

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Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 

 

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bed shear stress in shallow waters

RA
Rachel Allen, modified 4 Months ago.

bed shear stress in shallow waters

Youngling Posts: 2 Join Date: 10/27/18 Recent Posts

Hi,

I'm looking in to bed shear stress model outputs, and comparing to some ADV data collected in a shallow estuary (1-2 m MLLW, in  San Francisco Bay).  I'm a relatively new user for the Delft models, so I apologize if this is not the correct place for this question...

1) where are the bed shear stresses from currents, waves, and currents and waves reported?  I'm currently running the flow and wave modules in Delft3D4, and I've found that the trim file gives "bed shear stress", "staggered bed shear stress", and "max bed shear stress", and the trih file gives "bed shear stress".  I assume that these are bed shear stresses from currents and waves, tau_m (FLOW manual eq. 9.195) and tau_max (eq. 9.197).  But section 9.7.5 of the FLOW manual discusses tau_c and tau_w,  I'd love to determine if I can output those parameters from the model as well, and I haven't yet figured out how to do this from reading the manual.

2) how does the model account for wave penetration to the bed when computing bed shear stress?  My understanding is that wave spectra are reported for the surface, so tau_peak is the peak wave period at the surface.  But in this shallow estuary with tidal water level changing from 1 m above bed to 3 m  above bed, 2 second waves may penetrate to the bed on low water, but not on high water.  So, since tau_w is computed from u_orb, which is computed from omega (the wave frequency), the relevant omega to use at the bed may not be the same as at the surface where the waves are computed.  I would guess that this is accounted for in the model, but I haven't figured out how yet...  

Thank you for your help!

Best,

Rachel