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. 
 

** PLEASE TAG YOUR POST! **

 

 

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

 

 

Message Boards

underlayer/ initial bed composition problem

BY
Brendan Yuill, modified 3 Years ago.

underlayer/ initial bed composition problem

Youngling Posts: 1 Join Date: 4/11/13 Recent Posts
My model has 3 sand fractions of the same size: one fraction enters the domain at the upstream boundary (sediment feed), one fraction composes the domain bed in all grid cells except the top-most layer in 1 mid-domain cell (bed sediment), and one composes the top most layer in only that one mid-domain grid cell (simulating tracer sediment). Only one size fraction is supposed to enter the upstream boundary as defined by a time series in the .bcc file.

The initial bed composition is defined by 2 layers:

Layer 1 is 1 m thick at the cell with tracer sediment and 0.0 m thick everywhere else. It is fully composed of tracer sediment.

Layer 2 is 9.0 thick at the cell with tracer sediment and 10 m thick everywhere else. It is fully composed of the size fraction not simulating tracer sediment.

The transport layer thickness is set at 0.1 m, I am tracking 50 underlayers, each at 0.2 m thick.

Problems:

A small (< 0.01 kg/m2) amount of bed sediment is leaking out of the upstream boundary even though the .bcc file prescribes only the sediment feed fraction.

The map file indicates that at time zero, the 'sediment fraction top layer' is composed of an equal mixture of all three sediment fractions. The 'available mass of sediment' or 'sediment volume fraction' at time zero and z=1, equals that prescribed, i.e., the tracer sediment is only in 1 grid cell, not an equal mixture. However, at time 1, the 'available mass of sediment/sed vol. fraction' at time =1 indicates that a small amount of tracer sediment has likely entered the domain from the upstream boundary or something equally nutty.

What is the difference between the 'sediment fraction in the top layer' and 'sediment volume fraction' at z= 1...? Why might a small amount of sediment be entering my upstream boundaries despite by .bcc stating that for the modeled time period the input is zero? the equilibrium sand transport at the boundaries is turned off, of course.

Thanks for any and all help...I am stumped.