idealized, weakly stratified estuaries using GETM

[Kevin Chou]

Hello,

I am trying to use GETM to model idealized, weakly/partially stratified estuaries. I prescribed constant river runoff at the landward boundary, and tidal elevation variation at the seaward boundary with clamped type. No other 2D velocity and 3D boundary forcing are used. Since this is an idealized study, I don't know the 2D ocean velocity profile, so I cannot use the Flather condition.

Then comes the problem: at the seaward boundary, due to clamped, salinity of the whole water column is always S_ocean, and no freshwater is exiting the domain from the upper layer as in the highly stratified case. As a result, as the simulation progresses, due to the continuous freshwater supply from the upstream river, the whole estuary will be filled with freshwater. Therefore, no quasi-steady state can be reached. This is of course unwanted because, after many many tidal cycles, there is not any longitudinal salinity gradient in this case for me to investigate physical processes in tidally energetic estuaries, such as strain-induced periodic stratification. My understanding is that the freshwater input from the riverine boundary must be balanced by the upper-layer freshwater output at the ocean side, but that seems only possible in salt-wedge simulations.

Could anyone give me some hints or workaround for this issue? Thank you in advance.

Kevin