street gutter
Drainage ditches dug alongside a street, generally lined in concrete or another paving material.
In Japan these often are covered by a series of concrete slabs with slots between them to both allow drainage and act as handles to remove the slabs for repair or cleaning (see Danbooru post #3081063). The drainage ditch can also be covered by long metal grates as in Danbooru post #575226. These are usually placed between the roadway and a sidewalk, or create a sidewalk on their own.
For intermittent grates or gaps in a curbside that lead to a deeper underground sewer system, instead use storm drain.