Coastal resort area (7)
(Other definitions for riviera that I've seen before include "Coastal region with a nice climate" , "Warm coastal region" , "Subtropical 1 dn area" , "Mediterranean resort area" , "I arrive! (Anag)" .)
(Other definitions for seaside that I've seen before include "Holiday destination" , "A place on the coast" , "Old song 'I do like to be beside the . . . . . . .'" , "holiday venue" , "Coastal area" .)