Yellowstone County, MT Environmental Rules: Erosion Control (2026)

Section 27-1208.D(7) sets the baseline rule for any required landscaping: grass areas may be sodded, plugged, sprigged, or seeded, "except that sod or other erosion control products shall be used in swales, berms, or other areas subject to erosion," a plain instruction that ordinary loose seed is not good enough on slopes and drainage features likely to wash out. The same article's irrigation standards reinforce that rule for automatic systems: under Section 27-1208.F(1)(c), an irrigation system with a precipitation rate above 0.75 inches per hour is prohibited on any landscaped area larger than 1,000 square feet with a slope steeper than 30 percent, unless the landscape plan adds infiltration trenches, vegetated swales, bio-detention areas, or a similar county-approved facility to cut runoff, or the designer proves to the county's satisfaction that an alternative design will produce no runoff or erosion at all. Either way, the final landscape inspection has to confirm no runoff or erosion actually occurred before the project is signed off.

These standards apply only to landscaping installed under an approved zoning compliance permit; they are not a general grading or stormwater ordinance for construction sites at large. Broader erosion and sediment control tied to subdividing land in Yellowstone County falls under the county's separate Subdivision Regulations, a different set of rules from this zoning code.