Black winged stilts
I don't think so. These birds were quite small. Around 15 cm beak to tail.
Looks like a Sanderling in non-breeding plumage.
https://www.allaboutbirds.org/guide/Sanderling/photo-gallery/64814471
Nice photo!
Also, I do love the Delta (and the Ebre in general, travelled a lot of it's length this year up in Aragón)