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Deal all,

I have been trying to find the logic behind the way in which sediments are supplied to a river channel as bed load at the inlet, in the context of a 2D/3D TELEMAC simulation. There are many possible mechanisms for supplying sediments to a channel at an inlet, including: 1) setting the transport rate to the maximum rate that the flow can support (maximum transport capacity), 2) not supplying the channel with any sediment, 3) recirculating sediments that just got out of the channel at the outlet(s), 4) keeping inlet cell elevation constant, or 5) specifying specific rate(s) (steady or not). Although I read the TELEMAC and SYSIPHE user guides (and dictionaries), I'm not sure what logic is implemented in SISYPHE or if there are different options available.

I read the posts on "How do I set zero sediment inflow at the inlet", but my guess is that the topic was related to suspended load (and not bedload). The keywords "EQUILIBRIUM INFLOW CONCENTRATION" and "CONCENTRATION PER CLASS AT BOUNDARIES" are related to section 5.5 (Initial concentrations, boundary conditions) in SYSIPHE manual which is linked to suspended load.

Regards,
Yannick

Dear Yannick,
thanks for your post.
In Sisyphe you can impose the following boundary conditions.
For bedload sediment transport:
(i) by fixing the bed evolution to a constant value, that is, db/dt = 0 at specified boundary. In this case, the maximum sediment transport capacity is imposed directly, estimated by one of the well-known sediment transport formulae.
(ii) by specifying a specific sediment transport rate at boundary.

I suggest you to take a look to some of last post in the Forum, where this topic has been extensively aborded and discussed.

Typically, at outflow a Neumann-type BC is assumed, that is, the sediment just goes out.

For suspension transport, the concentration of each class can be specified through keyword CONCENTRATION PER CLASS AT BOUNDARIES. The keyword
EQUILIBRIUM INFLOW CONCENTRATION can be used to specify the value of the concentration at inflow, computed according to the choice of the REFERENCE CONCENTRATION FORMULA.

A new documentation that includes all these issues is coming out soon.

All the best,

Pablo

Hi Pablo,

I have developed a sediment rating curve based on field data and applied it at the boundary to my model. It turns out that the rate is much higher when compared with the values determined by the maximum sediment transport capacity. Thus, I got a lot of deposition by the upstream boundary.

To increase the maximum sediment transport capacity of the river, do I simply just multiple a factor to the bedload formula?

Edwin

Dear Edwin,
thanks for your post.
Let's suppose your equilibrium sediment discharge is q_b^* and that you have an 'extra' sediment inflow characterized by a percentage of your q_b^*, given by \Delta q_b^*. Then, it is valid to express your sediment discharge as:
q_b = q_b^*(1 + \Delta). Under this hypothesis, it is valid to express your 'modified' sediment discharge multiplied by a factor (1 + \Delta).

I hope it helps,

all the best,

Pablo