User Forum of Software BASEMENT

rghazanf

User

Registered: 2015-10-20

Posts: 9

suspended load_model input_format

Dear all,

I would like to ask you about the format of one model input.

BASEPLANE2D>MORPHOLOGY>SUSPENDEDLOAD>BOUNDARY>TYPE>suspension_discharge

According to the user manual, suspension discharge is an inflow boundary condition describing the suspended inflow in time ( a two column .txt data file t|c).

I wanted to kindly ask you:

1- what is the definition and unit of concentration herein? in the examples provided by tutorials I found that the "C" column is always defined by 1. For example in my case I have SSC of 150 g/l. What is the unit to which I shall convert this value?

2- If the SSC is an unsteady instantaneous source, indicating that at a certain moment (t=0) a suspended sediment laden flow is introduced to the channel and afterwards there is no source of SSC, how shall I define this in the input file as we don't have really a SSC hydro-graph? Does defining something like

t      c
0     c1
1      0
10     0
100   0

cause solution instabilities or not?

3- Consider that we have a closed hydraulic system with SS-laden flow. Due to some specific reasons, over the course of every cycle there is a loss of concentration which we don't know how much is. How can we define such a closed system in Basement? Is there anyway that it takes automatically the SSC value at the downstream boundary of the previous cycle and uses it as the SSC at the upstream boundary for the next cycle?

Your help would be great! Many thanks,

Reyhaneh

Daniel Ehrbar

Developer

Registered: 2014-09-05

Posts: 7

Re: suspended load_model input_format

Hi Reyhaneh!

(1) The suspension_discharge boundary condition requires a file with two columns, timestep and concentration. The concentration is given as a dimensionless unit: m3(suspension)/m3(water). If you have a water discharge of 0.47m3/s and define a concentration of 0.02 (=2%), then 0.0094m3/s of suspended load are conveyed into your model over this boundary. If you want a SSC of 150g/l, you need to convert this mass concentration into a volume concentration, which can easily be done via density of the suspended solids. You can check this out if you add a stringdef_history at the boundary (stringdef_values = conc). This output provides you mass fluxes in m3/s for each grain size. It can be applied to any stringdef in you model and is really useful to evaluate mass fluxes.

(2) Of course, you can as well define an in-stationary boundary condition. As long as the values are within a physically plausible range, there will no stability issues arise from this boundary condition.

(3) At the moment you do not have the option of a short-cut (closed hydraulic system), so you need to find another solution for this specific problem.

BASEd regards,
Daniel

rghazanf

User

Registered: 2015-10-20

Posts: 9

Re: suspended load_model input_format

Hi Daniel,

Many thanks for your response. I just would like to ask also about the following points

1- Regarding the boundary condition "Out_down"When we have just an upstream source of SSC with certain concentration, is it really necessary to define this "Out_down" condition for the downstream boundary? When do we really need to impose it?

2- What is the difference between these two choices for the upstream boundary (with specific steady concentration);
    a) defining "suspension_discharge" (t-c) 2- column data
    b) defining a ''source" of SSC

Many thanks for your great help.

Best regards,

Reyhaneh