Glenn County, CA Environmental Rules: Stormwater Management (2026)

010 requires every subdivision to be protected from flood hazard and inundation by storm water originating both on and off the property, with drainage facilities designed so water is carried through and off the site without injury to improvements, residential sites or adjacent land, and bars discharging drainage water onto existing county rights-of-way except as the public works director approves. 030 translates that into engineering numbers: drainage systems and bridges must pass a one-hundred-year frequency flood without damage, though systems draining less than one square mile may be designed to the ten-year standard if ponding from a bigger storm would cause no damage.

Pipes under driveway entrances need at least a twelve-inch inside diameter and a one-percent minimum slope where practical; pipes crossing streets need at least fifteen inches for concrete or eighteen inches for corrugated metal pipe, and all pipe in the right-of-way must carry a twenty-five-year design life. 020 requires drainage facilities to sit in a dedicated street, road, lane or public drainage easement, with a minimum twelve-foot easement for closed systems and twenty feet for open systems, and bars the county from maintaining any drainage facility outside a public right-of-way. 040, and new unlined drainage facilities cannot sit closer than fifty feet to an existing or proposed septic leach line. 050.