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## Message Boards

### Where is settling velocity included in vertical direction of transport eq.

GS

#### Where is settling velocity included in vertical direction of transport eq.

Padawan Posts: 54 Join Date: 6/25/16

Hi D3D-Delwaq community,

could you tell me, in which subroutine is the concentration (CONC) computed? In processes (waq_process) the CONC is a substance and other processes will be calculated through concentration. But which subroutin does compute the CONC? it comes from AD-transport equation. But which subroutine in waq_kernel is the transport equation for amass or CONC?

GS

#### RE: Where is settling velocity included in vertical direction of transport

Padawan Posts: 54 Join Date: 6/25/16

Dear Delwaq users, I found the answer :). It is considered in  trase2.f (line 200-Downward advection) in waq_process.

AM

#### RE: Where is settling velocity included in vertical direction of transport

Jedi Knight Posts: 222 Join Date: 1/26/11

The strategy in DELWAQ is to compute the mass balance - everything is converted to mass fluxes, these are summed and then the concentration is calculated from the mass and the volume. This necessarily differs per integration option. I fyou want to know the details, have a look in the routines dlwqn* - these are the main routines for each integration option.

GS

#### RE: Where is settling velocity included in vertical direction of transport

Padawan Posts: 54 Join Date: 6/25/16

Thanks Arjen. In sedim.f, the sedimentation flux (line 179,180 and 338) is calculated from CONC results. But how sedimentation flux will change the CONC?

AM

#### RE: Where is settling velocity included in vertical direction of transport

Jedi Knight Posts: 222 Join Date: 1/26/11

That is done i the very same way as all other fluxes: DELWAQ keeps track of the influence a particular flux has on a substance via a table of "stoichiometric" coefficients. For suspended sediment two fluxes are important: a flux from the water phase to the bottom material and the vertical transport (sinking of the material). Both are stored in the PMSA array, but have a different character - determined by the process definition. The exchange of material from the water phase to the bottom is a regular flux and represented by two stoichiometric relations:

dMwater/dt = - sedimentation flux

dMbottom/dt = + sedimentation flux

(Note: M is the mass in the segment)

For the sinking the flux as calculated is interpreted as a "flow velocity" on top of the flow prescribed by the hydrodynamics.