My suggestion is to have one of the above every 25 metres minimum.  Both are used for inspection of drains and routine cleaning.

Pits can be placed in a drive or pathway, with the surface graded to the opening.  This pit can then be used as an inspection/clean out point, as well as pick up any surface water.  Pits can also be placed in a garden or lawn area and fitted with a solid lid.

Inspection Openings are tees cut into the storm water drain and bought to the surface, with either a grate or screwed cap for easy access.