Wetlands Mitigation Program In South Carolina

J. Wayne Hall, Assistant Environmental Manager, South Carolina Department of Transportation, (803) 737-1872

Introduction

The South Carolina Department of Transportation (SCDOT) began mitigation banking in the early 1990's after encountering delays in project schedules due to mitigation concerns. Establishing mitigation banks for future project impacts was seen as a way of resolving numerous mitigation concerns prior to project completion. In the absence of practicable on-site opportunities, these banks would help avoid or minimize delays in project schedules by providing compensatory mitigation.

In 1996, the South Carolina Mitigation Bank Review Team (MBRT), which was established in accordance with the Federal Guidance under the oversight of the Charleston District Corps of Engineers, and is comprised of representatives from the US Army Corps of Engineers, the US Environmental Protection Agency, the US Fish and Wildlife Service, the National Marine Fisheries Service, the SC Department of Health and Environmental Control, and the SC Department of Natural Resources, approved a document entitled "The Establishment and Operation of Wetland Mitigation Banks in South Carolina." This document provides coordinated State/Federal guidance on the development and operation of wetland mitigation banks in South Carolina, and complements existing State and Federal regulations.

The SCDOT has three approved mitigation sites, with two additional sites under evaluation. An interagency Memorandum of Agreement (MOA) between the SCDOT and the signatory agencies, and a formal Banking Instrument is approved separately for each bank. Debits and credits for the banks are based on the Charleston District Corps of Engineers Standard Operating Procedures (SOP) or by preset ratios agreed upon by all signatory agencies. All of the SCDOT's mitigation banks are limited use or proprietary banks with use limited to the SCDOT. The mitigation banks are acquired using federal-aid funds. The development and approval process for establishing mitigation banks averages approximately two years. Examples of sites follow.

Sandy Island, Purchased and Protected

Sandy Island protects a diversity of natural and cultural treasures.

Sandy Island itself is an old plantation that has unique, sandy uplands surrounded by rivers that encompass high quality, coastal, forested wetlands. Wildlife includes many native and endangered species. The area contains numerous intact prehistoric and historic archaeological sites and a community comprised of descendants from the former plantation labor force.

The Sandy Island bank was developed to provide off-site mitigation credits to compensate for impacts to wetland resources resulting from future construction activities in the Coastal Plain of South Carolina. The development strategy used a partnering arrangement with numerous federal and state agencies as well as private environmental organizations. These efforts resulted in a $53,000,000 dollar cost savings on the Conway Bypass by reducing bridging over marginal wetlands. A portion of the cost savings from the Conway Bypass was then used to acquire Sandy Island. The Sandy Island Mitigation Bank is composed of part of Sandy Island along with parts of three other local plantations. The total cost for purchasing these tracts was $12.9 million, which included a $1 million dollar contribution by The Nature Conservancy.

The tidal and fresh water wetlands, the unique human communities, which are descendants of the slaves who worked the rice plantations, the endangered red-cockaded woodpecker, the pottery strewn throughout the island, and the undisturbed archaeological and historic cultural sites were all incentives to accomplish the acquisition of the island. All agencies involved set aside individual agendas to accomplish a larger goal.

The site contains approximately 17,000 acres of coastal plain habitat. Each acre is equivalent to one credit, with credits and debits applied using the Charleston District Corps of Engineers' SOPs. The bank was developed to provide mitigation for three to four major coastal plain projects. Presently, this bank has mitigated two major coastal plain projects. The remaining credits will be used to offset impacts on future coastal plain projects.

The SCDOT is responsible for the preservation, management, and monitoring of the properties, in perpetuity. While the SCDOT has continuing responsibility, the Department has entered into a management agreement with the Nature Conservancy for long-term management of the properties. According to the Sandy Island Banking Agreement, the SCDOT may convey the fee simple title to the Sandy Island tract and the three additional tracts to a suitable private or public entity. All existing covenants or easements would be conveyed with the transfer of the properties.

Sandy Island is open to the public for activities that will protect the natural state of the property, including hiking, bird watching, and fishing. Cultural and sociological studies are proposed to investigate the history of the Sandy Island residents. This community has remained relatively isolated from the outside world, as they continue to live on the island that is accessible only by water.

The acquisition of Sandy Island has proved to be a highly beneficial use of public funds and a compromise between increased cost of extensive bridging and natural habitat preservation. Sandy Island exemplifies the best aspects of private-public partnering. This project will protect an entire ecosystem in perpetuity and at the same time provide the South Carolina Department of Transportation the opportunity to proceed with a much needed transportation improvement program within the coastal plain of South Carolina.

Huspa Creek, Restored Hydrology Results in Marsh Restoration

Return of hydrology results in salt marsh restoration.

To mitigate highway construction impacts to tidal wetlands within the State, the SCDOT established the 250-acre Huspa Creek saltwater mitigation bank in Beaufort County, South Carolina. The site, which was approved in 1998, consisted of partially impounded estuarine tidal marshes and open water habitat formerly used for rice cultivation. A central dike and a number cross dikes and canals remained which greatly restricted the flow of water into the site from adjacent tidal streams. The primary function of the dike system was to isolate saline tidal circulation into a relatively narrow area west of the central dike, thereby converting the remainder of the site into freshwater rice fields.

To restore tidal hydrology, thirteen breaches were mechanically excavated in the central dike. These breaches helped open up most of the site to tidal inundation. This reduced the amount of open water habitat and is allowing the area to return to its natural condition of a Spartina alterniflora marsh. Spartina alterniflora, Juncus roemerianus, Distichlis spicata and Borrichia frutescens presently dominate the bank site. The outer perimeter of the area is composed of a mixed hardwood forest and wax myrtle scrub/shrub community. As tidal inundation increases the wax myrtle scrub/shrub and part of the forested communities are expected to be replaced with the aforementioned intertidal flora.

The service area covers the southern coastal plain of South Carolina, with northern coastal plain projects evaluated on a case-by-case basis. Debits and credits for the bank are based on the Charleston District Corps of Engineers SOPs. The total number of credits will range between 70 and 100, depending on the type of impacts and the proximity to the bank site.

Black River Basin, Restored Hydrology Rehabilitates Hardwood Swamp

A South Carolina creek in need of restoration.

The Black River Basin Mitigation Bank (BRBMB) is a 1709-acre site located southeast of Columbia in Clarendon County, South Carolina and was approved in 1994. The bank was a bottomland hardwood swamp that had been drained and logged. Lateral and transverse channels were excavated to facilitate the drainage of the swamp for forestry activities. The property was acquired by the SCDOT in order to restore the sites' natural hydrology and convert it into a functioning wetland.

Emerging Issues

Stream impacts are rapidly emerging as a priority concern for resource and regulatory agencies in South Carolina. The SCDOT is coordinating with "on-call" consultants who have working expertise in natural stream design to develop steps to address these agency concerns. A number of projects have been identified to incorporate their techniques and assess effectiveness.