South Dakota state law: grading and drainage

South Dakota law on grading and drainage is layered:

1. NO STATEWIDE BUILDING CODE. South Dakota is one of the few states without a state-mandated building code. SDCL does not adopt a uniform IRC/IBC; instead, each jurisdiction adopts its own. Sioux Falls and Rapid City adopt the current IRC, IBC, IMC, IPC, IECC, and IFC with local amendments. Smaller statutory cities may adopt older code editions or no code at all. Counties typically adopt the IRC by reference for unincorporated subdivisions but not for agricultural land. Grading, retaining-wall, foundation-drain, and lot-drainage standards therefore vary by jurisdiction.

2. IRC GRADING AND SURFACE DRAINAGE. Where the IRC is adopted, IRC Section R401.3 (Drainage) requires lots to be graded to drain surface water away from foundation walls, with a minimum 6-inch fall within the first 10 feet (a 5% slope) unless engineered alternatives are approved. IRC R401.4 covers soils tests; R405 covers foundation drainage. IBC Section 3304 covers excavation and grading for non-residential projects.

3. CONSTRUCTION STORMWATER PERMIT. Any project that disturbs 1 acre or more triggers the SD Construction General Permit under SDCL Chapter 34A-2 / ARSD 74:52, requiring a SWPPP and erosion/sediment BMPs including drainage and slope stabilization (see erosion-control entry).

4. LOCAL DRAINAGE ORDINANCES. Cities under SDCL Chapter 11-4 and counties under SDCL Chapter 11-2 may adopt drainage, detention, and grading ordinances, typical content includes minimum lot slope away from structures, prohibition on directing runoff onto neighboring property, sub-watershed detention sizing, easement requirements for drainage swales. Subdivision plats require approved drainage plans.

5. COMMON-LAW REASONABLE USE. South Dakota has adopted the 'reasonable use' rule for surface-water drainage between adjoining landowners (Knodel v. Kassel Township, 581 N.W.2d 504 (S.D. 1998); Mulder v. Tague, 85 S.D. 645 (1971)). An upper landowner may not unreasonably interfere with the natural flow of surface water onto a lower landowner, but reasonable improvements to one's own land that incidentally accelerate drainage are permitted if not unreasonably damaging.

6. AGRICULTURAL DRAINAGE. SDCL Chapter 46A-10A (Drainage of Agricultural Land) and SDCL Chapter 46A-11 (Drainage Boards) authorize county drainage commissions and provide a permitting process for tile drainage and other agricultural drainage works in rural counties.

7. FLOODPLAIN OVERLAY. Grading and fill in a FEMA Special Flood Hazard Area requires a local floodplain-development permit per the community's NFIP-compliant ordinance.

Violations of locally adopted IRC grading standards (typically R401.3 lot drainage and R405 foundation drainage) are code-enforcement matters with stop-work and certificate-of-occupancy hold authority. Construction stormwater violations (failure to control runoff from a 1-acre+ site) are enforceable by DANR up to $10,000/day under SDCL 34A-2. Discharging surface water onto a neighbor's property in an unreasonable manner is actionable as a private nuisance under SDCL 21-10-1 and at common law under Knodel/Mulder; remedies include damages and injunctive relief. Floodplain grading without a permit can trigger FEMA NFIP probation against the community.