All properties are responsible to properly manage drainage on their property by 1) maintaining runoff on their own property, 2) conveying runoff out to the street, or 3) conveying runoff to a recorded drainage easement that is in favor of the property. Sloping lots will require special grading attention, including V-ditches, swales, and rock/masonry walls. Slope cannot be steeper than 3:1 (three horizontal to one vertical) unless allowed by a stamped geotechnical report. Rock/masonry walls are required to be installed when slopes exceed 3:1.
When installing landscaping, fences, rock/masonry walls, etc., all required v-ditches, swales and berms must be reinstalled to return the drainage flow back to its original state. No alteration to the land of any kind can obstruct or alter the path of flow of any drainage easement used in the design of the subdivision to drain your lot and neighboring lots. See Typical Drainage Designs.
International Residential Code
R401.3 Drainage. Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection so as to not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6″ within the first 10′.
Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6″ of fall within 10′, the final grade shall slope away from the foundation at a minimum slope of 5% and the water shall be directed to drains or swales to ensure drainage away from the structure. Swales shall be sloped a minimum of 2% when located within 10′ of the building foundation. Impervious surfaces within 10′ of the building foundation shall be sloped a minimum of 2% away from the building.
