sponge reflection issue

[Ovel Díaz García]

Dear FUNWAVE-TVD users,  Happy New Year!! 

I created a 1D domain and added enough sponges at both ends. But I still get reflections (sawtooth noises) and can't eliminate them. I'm using the model's v3.6. My dx resolution is 0.25 m.

I'm attaching a figure of the domain and four eta plots at different times. You can see the reflection in both boundaries.  I was able to run the "surface_wave_1d" example, and it doesn't show any wave reflection.

What should I do to have no reflections in the sponges? My primary purpose is to get a time series at the station locations, but I would need to plot the global ETA solution, too.

Thank you