Planning for Isolated Wetlands

Transcription

1 Coastal Training Program North Inlet-Winyah Bay National Estuarine Research Reserve P.O. Box 1630 Georgetown, SC Ph. net Avoiding Wetland Alteration by Design Planning for Isolated Wetlands Highway 707 Murrells Inlet, SC Ph Fax

2 Introduction Wetlands What/Where/Why Hydric Soils Water Quality & Wetlands Isolated Wetlands Regulatory Jurisdiction Issues Project Planning Approach Development Strategies Land Planning for Wetlands Low Impact Development Concepts Bioretention vs. Natural Wetlands Constructed Stormwater Wetlands Conclusions

3 What are Wetlands? Why are they so important to Storm Water Management Definition: Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. Hydrology They act like sponges by retaining rainfall and then slowly releasing excess water during more arid seasons. Their temporary storage capacity helps reduce erosion and limit flooding. Habitat They provide temporary and permanent habitat for fish, plants, and other wildlife. Many endangered species and (according to some estimates) over 100 bird species, and 200 fish species depend on wetlands for survival. 50% of the waterfowl come from prairie pothole marshes, which represent 10% of the wetlands of the US. Water Quality They improve water quality by filtering inflow to lakes, rivers, and streams. The vegetation found in wetlands trap sediments and remove nutrients from runoff and surrounding soil. This reduces the growth of invasive species, which deteriorates waterway health by stealing the oxygen that plants and animals need for survival.

4 Soils & Wetlands - Hydric vs. Non-Hydric Soils

5 Water Quality & Wetlands Pollutant Removal Mechanisms Non-point source pollutants & their typical sources Sediments (agriculture, erosion, construction, utility installation) Nutrients (fertilizers, manure, organic waste) Oils and Greases (Cars, trucks, equipment) PAH s (vehicle emissions) Metals (vehicle emissions, manufacturing, fuel burning activities) Pathogens (bacteria/viruses pets, septic systems, wildlife) Pesticides/Toxic Chemicals (specific applications or spills) Physical Capture/Filtering trapping particles in vegetation/detritus, settling out in standing water bodies, adsorption to surfaces Biological Degradation breakdown of pollutants through physical or chemical processes Uptake of Nutrients plant materials utilize nutrients for growth, some plants can absorb metals and toxics

6 Water Quality & Wetlands Physical, Chemical & Biological Mechanisms Courtesy of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published: May 1999

7 Isolated Wetlands - Where do they fit in? Isolated wetlands are those wetlands that lack an obvious surface connection to downstream waters via ditch, stream, or continuous wetlands, such as gum/cypress ponds, Carolina Bays, and pocosins These wetland habitats have significant importance to amphibian species that rely on the seasonal and fish-free nature of isolated wetlands to successfully reproduce Isolated wetlands have historically been protected on a federal level through the Clean Water Act (CWA). Isolated wetlands comprise approximately 430,000 acres in South Carolina In 2001, the U.S. Supreme Court issued a decision in Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC decision) that called into question the federal government's ability to regulate isolated waters In 2006, the U.S. Supreme Court ruled in Rapanos v. U.S. that the Clean Water Act confers federal jurisdiction over non-navigable waters only if they exhibit a relatively permanent flow, such as a river, lake, or stream. In addition, a wetland is jurisdictional if there exists a continuous surface water connection (significant nexus) between it and a relatively permanent waterbody, This new ruling has potentially increased the amount of isolated wetlands depending on how this is defined by the ACOE Project Manager

8 Regulatory Jurisdiction Issues Wetland Regulation is a complex process that involves 14 state and federal agencies and depends on the current status of the wetland as a jurisdictional wetland subject to Section 404 of the CWA. Recent Court decisions have affected how jurisdiction is determined and what regulations and guidance will apply to these areas, specifically: Image courtesy of The Sun News Rapanos v. United States & Carabell v. United States (2006) Spectre, LLC v SCDHEC (2010) Jurisdictional Wetlands Subject to Federal Regulation Significant Nexus Determination Typically permitted jointly by USACE and SCDHEC Isolated Wetlands Subject to State Regulation Typically permitted by SCDHEC under the Stormwater Regulations

9 Regulatory Jurisdiction Issues Waters Protected under the Clean Water Act Rapanos & Carabell Guidance The agencies will assert jurisdiction over the following waters: Traditional Navigable Waters (TNW) Wetlands adjacent to traditional navigable waters Non-navigable tributaries of traditional navigable waters that are relatively permanent (RPW, i.e., the tributaries typically flow yearround or have continuous flow at least seasonally) Wetlands that directly abut such tributaries The agencies will decide jurisdiction over the following waters based on a fact-specific analysis to determine whether they have a significant nexus with a TNW: Non-navigable tributaries that do not typically flow year-round or have continuous flow at least seasonally Wetlands adjacent to such tributaries Wetlands adjacent to but that do not directly abut a relatively permanent non-navigable tributary The agencies will apply the significant nexus evaluation as follows: A significant nexus analysis will assess the flow characteristics and functions of the tributary itself and the functions performed by all wetlands adjacent to the tributary to determine if in combination they significantly affect the chemical, physical and biological integrity of downstream traditional navigable waters Significant nexus includes consideration of hydrologic and ecologic factors.

10 Regulatory Jurisdiction Issues Significant Nexus Determination TNW Traditional Navigable Waters RPW Relatively Permanent Waters Non-RPW RR Relevant Reach Adjacent Waters Image courtesy of EARTHWORKS

11 Regulatory Jurisdiction Issues Isolated Wetlands Subject to State Regulation Typically permitted by SCDHEC under the Stormwater Regulations SC Supreme Court Decision in February 2010 affirmed that the SC Coastal Management Program (CMP) was valid and applicable in the coastal zone Image courtesy of EARTHWORKS All projects that require state or federal permits (such as stormwater, water and sewer construction permits, air emissions, etc.) are affected and require a Coastal Zone Consistency Certification prior to permit issuance

12 Project Planning Approach Section 404(b)(1) provides a three-step sequence for mitigating potential adverse impacts to wetlands - first avoidance, then minimization, and lastly compensation for unavoidable impacts to aquatic resources. Identify-Avoid-Minimize-Mitigate Identify aquatic resources on your project site to determine size, type, and location (what are your assets and where are they) Land Planning should avoid aquatic resources and utilize these areas for storm water management, green space, and natural areas Unavoidable Impacts must be minimized to the extent practicable to achieve the project goal (bridging, limiting access points, bulkheads, etc.) Compensatory Mitigation required to offset the adverse affects of wetland fill On-site Mitigation (protective buffers, restoration, creation) Off-site Mitigation (Project Specific locations) Mitigation Credits

13 Isolated Wetland Development Strategies The overall project goal highest and best use of the land Developers should view wetlands as a resource to be valued The overall asset value is the sum of the location, soils, drainage, view corridors, vegetation and trees, zoning, and other natural resources Isolated wetland areas typically have poor soil conditions which can increase the cost of road or building construction Isolated wetlands can have vegetation that provides screening buffers and aesthetic values Combining isolated wetlands with Low Impact Development (LID) techniques can reduce overall development costs Isolated wetlands in combination with bioswales/grass filter strips can provide a portion of the overall stormwater management Maximize the asset value by recognizing all characteristics and integrating them into the project

14 P.O. Box 1630 Georgetown, SC Ph. Land Planning For Wetland Protection Isolated Wetlands left undeveloped can provide: Stormwater functions Buffer and screening functions Open space functions Education opportunities Conservation Development consists of utilizing land in a manner that maximizes the amount of open space while maintaining density. Conservation Development has 4 basic steps (i) identifying primary and secondary conservation areas, (ii) designing open space to protect them, (iii) arranging houses outside of those protected areas, and (iv) finally laying out streets, lots, and infrastructure Image courtesy of Resourceful Communities Program

15 What is Low Impact Development? How can it be applied to Isolated Wetlands? Definition: Low Impact Development (LID) is an innovative stormwater management approach with a basic principle that is modeled after nature: manage rainfall at the source using uniformly distributed decentralized micro-scale controls. The goal of LID is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. LID addresses storm water through small, cost-effective landscape features located at the lot level instead of conveying, managing and treating storm water in large, costly end-of-pipe facilities located at the bottom of drainage areas. LID utilizes Integrated Management Practices (IMP) as the building blocks for a complete stormwater treatment system

16 Integrated Management Practices Landscaping Tools Native Groundcover Landscaping Filter Strips Bioretention* Rain Gardens* Bioswales* Image courtesy of * DESIGNED TO MIMIC WETLAND FUNCTIONS

17 What is Bioretention? Definition: An engineered process to manage storm water runoff, using the chemical, biological and physical properties afforded by a natural, terrestrial-based community of plants, microbes and soil. Bioretention provides two important functions: (i) water quantity (flood) controls; and (ii) improve water quality through removal of pollutants and nutrients associated with runoff. Image courtesy of Sustainable Stormwater Water Quantity Bioretention facilities act like sponges by retaining rainfall and then slowly releasing excess water during more arid seasons. Their temporary storage capacity helps reduce erosion and limit flooding. Water Quality Bioretention facilities improve water quality by filtering inflow to lakes, rivers, and streams. The vegetation traps sediments and remove nutrients from runoff and surrounding soil. This reduces the growth of invasive species, which deteriorates waterway health by stealing the oxygen that plants and animals need for survival. Image courtesy of Low Impact Development Center DESIGNED TO MIMIC WETLAND FUNCTIONS

18 Bioretention Structure and Function Bioretention facilities (e.g. rain gardens) may range from simple shallow depressions to more complex designs, but all are structurally engineered to provide the following functions with respect to stormwater quantity control: interception, capture, infiltration, filtration, storage, and water uptake by vegetation. The 9 major bioretention facility components are: Pretreatment Flow Entrance Ponding Area Plant Material Organic Layer or Mulch Planting Soil and Filter Media Pea Gravel Diaphragm Underdrain and Outlet Surface Overflow DESIGNED TO MIMIC WETLAND FUNCTIONS Image courtesy of Low Impact Development Center

19 Pretreatment allows settling and filtering of sediments and suspended solids at the entry point Vegetated Buffer Strips and grass buffer strips provide an extra level of pretreatment Pretreatment methods can include: Forebay Pretreatment swale/channel Mulch layer Sand filter layer Gravel diaphragm Upflow inlets Flow entrances reduce the water velocity and dissipate erosive energy Sheetflow over grassed area is preferred but not always available due to site constraints Flow entrances can include: Landscape stone Surge stone Riprap aprons Upflow inlets P.O. Box 1630 Georgetown, SC Ph. Pretreatment/ Flow Entrance For Isolated Wetlands Image courtesy of Low Impact Development Center Image courtesy of Bioretention.com

20 Ponding Area/Overflow Ponding area provides surface storage of the runoff and allows evaporation to occur Settling of particulates occurs in the ponding area for additional treatment of runoff Ponding design depths are a function of the shape and size of the isolated wetland Image courtesy of Low Impact Development Center Overflow from isolated wetlands may need to be part of an engineered piping system (engineered outlet set to design elevation) or surface swale that flows into overall storm water management system Image courtesy of Low Impact Development Center

21 Plant Material Plant species bind nutrients and other pollutants through trapping and uptake Plants remove water through evapotranspiration Plant roots create pathways for infiltration Roots provide a media for bacteriologic growth A variety of plants increases biologic diversity and reduces insect and disease infestation Vegetated areas provide wind breaks, reduce heat island effects, and improve aesthetics for development Plant materials support wildlife habitat and absorb noise Image courtesy of Low Impact Development Center

22 Constructed Stormwater Wetlands Constructed wetlands should connect into the existing drainage run at similar elevation to reduce runoff velocity A constructed stormwater wetland can achieve high removal rates of particulate and soluble pollutants (nutrients) through gravitational settling, wetland plant uptake, absorption, physical filtration, and biological degradation Native species are selected to ensure success Imported hydric soils add seedstock and rootstock to the plantings to improve success Planting helps to reduce invasive species DESIGNED TO MIMIC WETLAND FUNCTIONS

23 Conclusion Isolated wetlands can provide valuable ecological benefits Water quality and wildlife habitat are primary functions Isolated wetlands are regulated based on their place in the landscape State regulations specifically address isolated wetlands in the Coastal Zone Utilize wetland resources for their aesthetic and natural values Minimize wetland impacts through alternatives analysis and proper land planning this reduces permitting time and costs Managing stormwater at the source with distributed controls can reduce development costs LID/Bioretention can be applied to existing isolated wetlands to provide a positive benefit to the developer and homeowner Current trends are to create more natural management systems costs can be reduced by utilizing what is in place and minimizing construction