Project Summary

The Low Impact Development (LID) Manual for Coastal South Carolina project is supported by years of outreach and research led by the South Carolina National Estuarine Research Reserves (NERRS) and South Carolina Sea Grant Consortium. The project includes key leaders in the area that serve on the LID Manual Advisory Committee, and incorporates public trainings/meetings throughout the process. The final product will be a guidance document defined and vetted by end users.

Background

Low Impact Development (LID) is an approach to land development (or redevelopment) that works with nature to manage stormwater as close to its source as possible (US EPA 2014). Years of research and community engagement indicated the need for an LID manual for the South Carolina coast. A number of scoping workshops, focus groups, and a survey of engineers, planners, developers, and other design professionals resulted in a formal content assessment for the LID manual.

The Ashepoo-Combahee-Edisto (ACE) Basin and North Inlet-Winyah Bay (NIWB) NERRs, South Carolina Sea Grant Consortium, and Center for Watershed Protection collaborated to secure $329,943 in funding from the NERRS Science Collaborative to develop the manual. This two-year project (2012-2014) aimed to provide local decision-makers with stormwater engineering specifications, land use planning resources, and site design practices that are tailored to the conditions of the South Carolina coast.

Implementation

The overall goal of the project was to create an interdisciplinary, user-defined LID Manual for Coastal South Carolina through a series of collaborative meetings with researchers, engineers, planners, landscape architects, and other practitioners. The Manual was designed serve as a source of coastal-specific LID information, tools, and resources for South Carolina. The project had many collaborators as part of the LID Manual Advisory Committee, including local government representatives, state representatives, private consultants, and researchers, among others. The background research conducted as part of the manual’s construction stemmed from several sources as: 1) local research efforts; 2) national research for LID, stormwater, and watershed management; 3) other southeast LID manuals; 4) southeast climate experts; and 5) state stormwater accounting tools and supporting data.

Part of the project assessed future coastal climate impacts and potential stormwater management solutions in South Carolina. Many of the underlying assumptions that stormwater engineers use for stormwater management and design could become outdated if the predicted climate impacts on the water cycle become a reality. A Climate and Stormwater Roundtable workshop was held in September 2013 to facilitate information exchange between climate specialists and to convey climate change information in terms of stormwater management concerns. Twenty-four climate specialists, engineers, developers, engineers, and researchers met to discuss climate change, sea level rise, and resulting impacts on LID best management practices (BMP). By discussing the best available climate science research, the project team was able to determine the feasibility of incorporating climate change considerations into proposed BMP specifications and planning recommendations, thus making the LID strategies outlined in the manual viable tools for climate adaptation.

Climate change threatens to alter the hydrology of the South Carolina coast by increasing flood frequency and intensity, along with potentially raising groundwater levels. Similarly, landscape and site design also have the potential to be impacted by increased flooding due to storms or rising sea levels. The key variables in the BMP specifications and corresponding compliance spreadsheet include total annual rainfall and storm intensity, which affect the design storm, and sea level rise, which may impact where BMPs can be located, in addition to their design. The number of storm events in a given year, storm intensity, and changes in the seasonality of rainfall can also have an impact on LID principles and practices; therefore, looking forward, LID guidance may need to be adapted to account for regional climatic changes. Unfortunately, the Southeast is the only region of the country for which the currently available major climate models do not agree in terms of expected future precipitation. While most climate models agree that the intensity of large rainfall events is likely to increase, these projections vary from a 3% to 40% increase in rainfall, both of which will have dramatically different outcomes in terms of conveyance, storage, and treatment capacity.

Outcomes and Conclusions

The LID Manual was released in 2014 and includes site design development principles, conservation and protection tips, coastal climate findings, LID stormwater management specifications and design details, and spreadsheet tools to support LID planning and implementation. The overall goal of the manual is to provide local decision makers with the knowledge and resources to apply LID practices on the community, neighborhood, and site scale.

Considering that local communities have the most to lose for not considering climate adaptation measures, the LID Manual includes some guidance on how to pursue climate adaptation through stormwater management. These strategies are included in an appendix titled “Adapting Stormwater Management for Climate Change”:

• implementing LID practices at the site scale in order to maximize overall system resilience;
• modifying practices to prevent bypass during intense storm events (e.g., bioretention, pretreatment for rainwater harvesting);
• periodically revisiting design storms and mapped floodplains (i.e. applying adaptive management principles to LID BMPs);
• creating adaptable planting plans (e.g., will native plants be well-suited for different climate regimes or will other plants fare better?); and
• using stormwater as a resource (e.g., irrigation demand, stormwater harvesting).

Citation

Keppler, B., G. Hoffman, S. Drescher, A. Turner, & K. Ellis. (2021). Low Impact Development Manual for Coastal South Carolina [Case study on a project of the ACE Basin and North Inlet-Winyah Bay NERRs, South Carolina Sea Grant Consortium, and Center for Watershed Protection]. Version 2. Ed. Rachel M. Gregg. (Last updated April 2021)