A major storm flow route is the planned overland path for runoff when the minor system—typically catchbasins and storm sewers—is exceeded, blocked or unavailable. It directs exceptional flows toward a safe outlet without flooding buildings or creating unacceptable impacts on neighbouring property.
Minor and major systems work together
The minor system manages more frequent rainfall through pipes, inlets and controlled facilities. The major system uses surface grading, roadways, swales and designated overflow routes for larger events or system failure. A design needs both because no inlet or pipe can be assumed to capture every possible flow.
The route is shown with elevations, flow arrows, sags, high points and spill locations. Review may consider depth, velocity, building openings, emergency access, erosion and downstream effects. A route that crosses a property line or depends on an unconfirmed easement is a material design issue.
Public-space coordination
In parks, a major route may pass through open space, but it should not be improvised across play areas, accessible paths or building entrances. Sports fields and dog off-leash areas can sometimes participate in controlled surface storage, provided drainage, safety, recovery time and maintenance expectations are addressed.
Bous Engineering develops major-flow concepts through coordinated grading plans. See why site grading matters early and how drainage differs from stormwater management.
Key takeaway
A major flow route is a deliberate backup system, not simply wherever water happens to go. Reserve and verify it early so later building, landscape and accessibility decisions do not block the safe path.
Bous Engineering supports servicing, stormwater, grading and municipal approval assignments across Eastern Ontario.