The Southern Lowcountry Stormwater Design Manual serves as a comprehensive technical and administrative guide for managing stormwater within the South Carolina Lowcountry. Effective as of September 14, 2021, and recently amended on March 11, 2025, the manual establishes standardized procedures and design criteria to protect the region’s sensitive water resources from the adverse impacts of land development and redevelopment. Its primary purpose is to safeguard local ecosystems by managing stormwater runoff quality, volume, and peak discharge through the implementation of specialized Best Management Practices (BMPs).
The manual provides a rigorous framework that spans the entire project lifecycle—from initial site assessment and “Better Site Design” planning to construction inspections and long-term maintenance obligations. By integrating natural resource protection with modern engineering standards, the manual ensures that development in the Southern Lowcountry maintains the integrity of vital watersheds, such as the May and Savannah Rivers
The Southern Lowcountry Stormwater Design Manual (amended March 11, 2025) provides a comprehensive framework for managing stormwater in the South Carolina Lowcountry. It establishes technical standards and administrative procedures for site planning, design, and long-term maintenance of stormwater best management practices (BMPs).
Core Purpose and Applicability
The manual is designed to protect local water resources from the impacts of land development by managing stormwater runoff quality, volume, and peak discharge. It applies to regulated development and redevelopment projects within the region, establishing specific performance requirements based on “Watershed Protection Area” designations.
Key Components and Requirements
The manual is structured into six primary chapters and several detailed appendices:
- Design and Permitting (Chapter 2): Outlines a multi-step site planning process including natural resource inventories and “Better Site Design” principles to minimize impervious cover. It details submittal requirements, construction inspections, and the necessity of recorded maintenance agreements.
- Performance Standards (Chapter 3): Defines specific control requirements, including:
- Stormwater Retention Volume (SWRv): Standards for retaining a specific volume of runoff on-site.
- Watershed Protection Areas: Specific mandates for areas like the Savannah River and Bacteria & Shellfish protection zones.
- Maximum Extent Practicable (MEP): Guidelines for meeting standards when site constraints exist.
- Stormwater Best Management Practices (Chapter 4): Provides exhaustive technical specifications, design criteria, and maintenance tasks for various BMPs. Key practices include:
- Bioretention and Permeable Pavement: For retention and pollutant removal.
- Infiltration Practices and Green Roofs: Focused on reducing runoff volume.
- Rainwater Harvesting and Open Channel Systems: Including dry swales and grass channels.
- Stormwater Wetlands and Ponds: Primarily for managing larger storm events (2- to 25-year floods).
- Erosion and Sediment Control (Chapter 5): Establishes criteria for managing soil disturbance during construction to prevent downstream sedimentation.
- Enforcement (Chapter 6): Details the legal framework for violations and enforcement actions under the Unified Development Ordinance (UDO).
Compliance and Maintenance
A critical aspect of the manual is the focus on the entire lifecycle of stormwater infrastructure. This includes:
- As-Built Submittals: Required within 21 days of construction completion to verify the site matches approved designs.
- Ongoing Inspections: Regulated BMPs must be inspected at least once every three years by a certified professional to ensure continued functionality.
- Maintenance Agreements: Property owners must record legal covenants ensuring the long-term upkeep of stormwater facilities.
The Southern Lowcountry Stormwater Design Manual establishes a robust regulatory and technical framework intended to ensure that land development proceeds in harmony with the region’s unique ecological needs. By integrating rigorous performance standards—such as the Stormwater Retention Volume (SWRv) —with comprehensive best management practices and long-term maintenance requirements, the manual provides the tools necessary to mitigate the impacts of urbanization on vital local watersheds. Ultimately, the successful implementation of these guidelines depends on the continued collaboration between developers, engineers, and local authorities to uphold the manual’s standards, thereby preserving the water quality and natural beauty of the Southern Lowcountry for future generations