Executive Summary

Stormwater Ordinance

The Southern Lowcountry Stormwater Ordinance is a model ordinance to address post-construction stormwater management in the Southern Lowcountry Region. It was developed by a committee of representatives of the Region’s participating jurisdictions including Beaufort County, Jasper County, the City of Beaufort, the Town of Bluffton, the City of Hardeeville, and the Town of Port Royal. Upon the Ordinance adoption, participating municipalities/jurisdictions will reference the Southern Lowcountry Stormwater Design Manual. The Ordinance directs residents, land developers, redevelopment and government permit applicants to submit details and plans that comply with this design manual. The Ordinance requires maintenance and inspection agreements to be recorded with property ownership and authorizes inspections and enforcement by the jurisdictions. When passed by each of the jurisdictions a unified program for stormwater management will go into effect across the Southern Lowcountry Region.

View the Stormwater Ordinance

Stormwater Design Manual

This Manual and the design criteria presented within represent good engineering practice and should be used in the preparation of stormwater management plans. The criteria are intended to establish requirements, minimum standards, and methods for sound planning, design, and review process. It is intended to guide the stormwater design review of proposed work done by developers, private parties and governmental agencies.

Chapter 1: Background, Purpose, and Administration - View Full Text

This Manual’s purpose is to provide a unified framework for designing a stormwater management system to:

Improve water quality through runoff reduction to the maximum extent practicable (MEP);
Prevent downstream stream bank and channel erosion;
Reduce downstream overbank flooding; and
Safely pass or reduce the runoff from extreme storm events.

Design criteria in this Manual are applicable to any new development or redevelopment activity that meets one or more of the following criteria:

New development that involves the creation of 5,000 square feet of impervious surface or that involves other land disturbing activities of one acre or more.
Redevelopment that involves the creation, addition or replacement of 5,000 square feet or more of impervious surface or that involves other land disturbing activities of one acre or more.
New development or redevelopment, regardless of size, that is part of a larger common plan of development.
A major substantial improvement of an existing property, which is defined as a renovation or addition to a structure that meets specific cost and size thresholds.

Chapter 2: Design Review and Permitting Process - View Full Text

This manual requires a comprehensive set of site planning and design criteria that must be applied to new development and redevelopment activities occurring within the Southern Lowcountry region, including implementing Better Site Design (BSD) and completing a natural resources inventory. Satisfying these criteria promotes the systematic development of acceptable stormwater management plans, and a successful integration of natural resource protection and stormwater management through the site planning and design process. This Chapter also discusses the requirements for the stormwater management plan (SWMP); construction inspections; maintenance agreements and responsibilities; and as-built submittals.

Chapter 3: Minimum Control Requirements - View Full Text

It is the intention of this Design Manual that all proposed development, redevelopment, and major substantial improvement shall provide stormwater quality control on-site to the maximum extent practicable (MEP) for the Stormwater Retention Volume (SWRv) for Watershed Protection Areas and/or Special Watershed Protection Area. Two levels of stormwater retention are prescribed, the 85th and the 95th percentile storm, and are assigned based on a site’s subwatershed as identified by the U.S. Geological Survey Hydrologic Unit Code 12 (HUC-12) presented in Section 3.5. In addition, peak discharge control of the post-development 2, 10, 25 and 50-year, 24-hour storms to their predevelopment flow shall be provided by a combination of structural controls, GI/LID practices and other non-structural BMPs. Furthermore, requirements to manage the 100-yr, 24-hour storm event are provided in the extreme flood event (section 3.8). Stormwater ponds are considered the least favorable structural best management practice to meet the SWRv and water quality requirements of this Manual.