Everyman crossword 3424

[robbiejay]

Last clue, 16ac French river certain to cover miles (5) s-m-e. I think it has to be the somme, but I can't see the clue in this. Any help gratefully appreciated,

[mahonia]

Somme

[bibblebub]

certain = SOME, as in 'certain people are not what they seem'
miles = M

SOM m E

[robbiejay]

Many thanks mahonia and bibblebub, I missed the connection between some and certain, again thanks.