Unless otherwise approved by the plan commission, street grades shall conform in general to the terrain and shall be not less than 0.35% nor more than 5%. Street grades shall be such as to provide natural surface drainage of storm water regardless of the presence or absence of storm sewers. The intent is to avoid depressions or inverts that will flood in flash storms, or for which storm sewers are inadequate.
('69 Code, App. B, § 6.13)