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HomeMy WebLinkAboutNHC Stormwater Technical Report_04_2025 New Hanover County Stormwater Technical Report 2025 Prepared by Virginia Norris, 2025 New Hanover County Stormwater Technical Report 1 Introduction Stormwater management is a key issue in New Hanover County due to its coastal location, rapid development, and flooding risks. Rainfall running over impervious surfaces collects pollutants, increasing runoff and impacting waterways, ecosystems, and aging stormwater infrastructure. This report examines current regulations and strategies for managing stormwater, identifying challenges and potential improvements to enhance water quality and reduce flooding risks. Stormwater Regulations, Policies, and Standards In North Carolina, stormwater management regulations are a shared responsibility between the state and local governments, including counties. The North Carolina Department of Environmental Quality (NC DEQ) sets state-level rules to protect water quality, control runoff, and prevent flooding, while counties are responsible for implementing and enforcing these rules locally. Counties can adopt stricter regulations tailored to local needs, such as addressing specific environmental concerns or flooding issues, and are responsible for issuing permits, conducting inspections, and ensuring compliance. While the state provides guidance and oversight, New Hanover County plays a key role in the day-to-day management of stormwater, working in coordination with the state to ensure effective stormwater control across the region. Regulations for stormwater management are adopted under the authority granted by the General Assembly of North Carolina and are applicable to all territory within the unincorporated areas of New Hanover County. New Hanover County Stormwater Management Ordinance The New Hanover County Stormwater Management Ordinance, approved in September 2000, is a regulatory document designed to manage stormwater runoff and reduce the risk of flooding. It defines key terms, outlines jurisdiction, and aligns with state and federal regulations, establishing requirements for new developments, including discharge limits, mitigation measures, and control structures. A permitting process mandates stormwater management plans, inspections, and ongoing maintenance responsibilities for property owners. The ordinance also sets design standards, requiring Stormwater Control Measures (SCM) and erosion control measures. It includes enforcement provisions detailing violations, penalties, and compliance measures, along with special provisions for sensitive areas like wetlands and floodplains, exemptions, and coordination with other environmental laws. New Hanover County Stormwater Design Manual The New Hanover County Stormwater Design Manual provides guidelines for stormwater management in unincorporated areas, detailing performance, and design for stormwater systems. It aligns with local, state, and federal regulations, including the New Hanover County Unified Development Ordinance, NCDEQ Stormwater Minimum Design Criteria, and the Federal Clean Water Act. The manual defines the roles and responsibilities of the county, designers, and property owners in ensuring compliance, with key components like permit applications, hydrologic design criteria, runoff methods, and stormwater control measures. Key regulations include: • New Hanover County Unified Development Ordinance (Articles 6, 7, 9) New Hanover County Stormwater Technical Report 2 • NCDEQ Coastal Area Management Act Regulations • NCDEQ Water Supply Watershed Regulations • NCDEQ Dam Safety Program • NCDEQ Stormwater Minimum Design Criteria • NCDEQ Post-Construction Stormwater Program • NC Department of Transportation Standard Specifications for Roads and Structures • Federal Clean Water Act (Sections 401 and 404) • Federal Emergency Management Agency Floodplain Regulations In cases of conflict between laws, the more stringent requirement applies unless limited by state or federal law. New Hanover County Unified Development Ordinance New Hanover County’s Unified Development Ordinance establishes stormwater management policies, requiring property owners to maintain stormwater systems and new developments to implement measures preventing increased runoff rate. A Drainage Plan is required for most developments, to ensure existing drainage patterns are maintained and direction of stormwater runoff is appropriate. Projects creating 10,000+ square feet of built-upon area need a Stormwater Permit and Management Plan, and the county reviews applications with automatic approval if no action is taken within set time limits. Variances can be granted if alternative designs offer equal or better control, and the county enforces compliance through inspections and corrective actions. NHC Stormwater Services Program The New Hanover County Stormwater Services Program, established in 2020, ensures ongoing maintenance of stormwater systems in unincorporated areas. Developed after exploring the program in 2017, it relieves property owners of the responsibility for maintaining ditches and pipes, with county crews handling tasks like sediment removal, culvert installation, and ditch work. The program is funded through a special revenue fund and billed as a separate fee on annual property tax bills. Areas of Concern The New Hanover County Department of Engineering logs public drainage reported issues and concerns, mapping locations to identify areas at risk during flood events. With approximately 785 reported issues, most in the southern county, crews managing up to 70 ongoing work orders for maintenance. The stormwater services division of the engineering department consists of one chief engineer, one associate engineer, two field investigators, one superintendent, one construction crew and one maintenance crew. The construction and maintenance crews consist of one supervisor and four laborers for each crew. Current Engineering Projects Streamgage Streamgages are vital for monitoring water levels and flow in streams, rivers, and reservoirs. The USGS operates one active streamgage, while New Hanover County Engineering manages eight, with New Hanover County Stormwater Technical Report 3 two more being deployed. These devices record data every 15 minutes, with increased frequency during floods, transmitting it to a central system. The data aids in flood forecasting, infrastructure management, and planning. The county plans to expand monitoring with ten more streamgages. Capital Improvement Projects New Hanover County has 150 mapped capital projects, with 89 in the northern part and 61 in the south. Currently, 14 projects are in the design phase with consultants, and county engineers are designing seven more. Nine projects are fully designed and awaiting construction. In total, 160 projects require engineering evaluation, including 110 in the county’s five-year plan and 50 newly added, with some evaluations handled by consulting engineers and others by the Engineering Department. Other Projects While much of the work now is reacting to the issues reported to the county by residents, the department is continually working towards shifting from a reactive to a proactive approach. There are plans in the future to conduct additional watershed studies beyond Pages Creek, as well as planned improvements. The engineering team is currently focused on a process of maintenance, repair, and improving the system. They are working to enhance its performance and ensure long- term reliability. New Hanover County Stormwater Technical Report 4 Current Capital Improvement Projects Projects in Design with On-Call Consultants Design by New Hanover County Engineers Design Complete; in Queue for Work Order • Channel Haven Road Stream Bank Restoration • Courtney Pines Road Culvert Replacement (survey only) • Battle Park Subdivision Ditch and Culvert Improvements • Sandybrook Road to Overlook Drive Ditch and Pipe Replacement (survey only) • Horn Road to Long Branch Drive Ditch Improvements (survey only) • CFPUA WTP Ditch Extension (survey only) • Peters Lane to Orpin Court Ditch and Pipe Evaluation • Richardson Drive Ditch and Pipe Improvements • Horndale Road and Colchester Court Ditch Improvements (survey only) • Vowel Avenue Culvert Evaluation • Daniel Boone Trail and Daisy Lee Drive Culvert Evaluation • Queens Point Community Watershed Study • Heritage Park Community Watershed Study • Stumpy Court Pipe Evaluation • Courtney Pines Culvert Replacement • Sandybrook Road to Overlook Drive Ditch and Pipe Replacement • Horn Road to Long Branch Drive Ditch Improvements • CFPUA WTP Ditch Extension • Horndale Road and Colchester Court Ditch Improvements • Willow Way Ditch and Pipe Evaluation • Stillwell Road Pipe System Replacement • Brown Pelican Culvert Replacement and Ditch Improvements • Stillwell Road Pipe System Replacement • Castle Hayne Fire Station Outfall • Salem Court Ditch Improvements • Rothbury Court Pipe Replacements • Retriever Road Pipe Replacements • 7664 Market Street Pipe Replacements • Beresford Court Ditch Improvements • 3421 Lynn Avenue Pipe Improvements New Hanover County Stormwater Technical Report 5 NHC Water & Soil Conservation District The New Hanover Soil and Water Conservation District (NHSWCD) works to protect and enhance soil and water resources in New Hanover County through partnerships with local, state, and federal agencies, including New Hanover County, the City of Wilmington, the NC Department of Agriculture and Consumer Services, and the USDA Natural Resources Conservation Service. These collaborations provide cost-share funding and technical assistance to local citizens while fostering conservation efforts with organizations like the Wilmington-Cape Fear Home Builders Association. Soil and Water Conservation Districts were authorized in North Carolina in 1937 and operate under local control with support from state and federal resources. NHSWCD, part of Area 6 among North Carolina’s 96 districts, oversees conservation plans, educational programs, and coordination of resource management efforts across multiple agencies. Pages Creek Watershed Restoration Plan The Pages Creek Watershed Restoration Plan, led by the New Hanover Soil and Water Conservation in collaboration with local partners, aims to address pollution and improve water quality in the Pages Creek watershed, which has high contamination levels due to stormwater runoff, impacting shellfish harvesting. The plan includes green infrastructure projects like living shorelines to reduce erosion and bioretention areas to filter pollutants, along with a feasibility study upstream of Dunbar Road for stream restoration, watershed improvements, public access, and flood resilience. The plan was approved by the North Carolina Division of Water Quality in January 2024, adopted by the NHC Soil and Water Conservation District Board in February, and received funding approval in July, with the first phase set to begin in early 2025. Other Programs 1. Heal Our Waterways • The City of Wilmington, in partnership with New Hanover SWCD and local organizations, created the Heal Our Waterways (HOW) program to reduce polluted runoff in Bradley and Hewletts Creeks by educating residents and providing resources. Through HOW, residents may qualify for full funding to install approved stormwater catchment devices, with New Hanover SWCD recently implementing several best management practices in these areas. 2. NHC Water Quality Improvement Program • New Hanover County offers a 50% matching fund for residents in unincorporated areas to install approved Best Management Practices (BMPs) like rain gardens, swales, and cisterns to reduce stormwater pollution. Eligible residents, who do not pay municipal property taxes, can provide their match through payment or in-kind labor. 3. Community Conservation Assistance Program • The Community Conservation Assistance Program (CCAP) provides up to 75% reimbursement for installing stormwater BMPs on properties developed for at least three years to improve water quality. Administered by local Soil and Water Conservation Districts, including NHSWCD, the program supports homeowners, businesses, schools, and community groups through a two-phase application process involving ranking, site visits, and design approval. New Hanover County Stormwater Technical Report 6 4. Agriculture Cost Share Program • The Agriculture Cost Share Program in New Hanover County covers up to 75% of BMP installation costs for farmers, including horse farms and timber owners, to improve water quality, with the remaining 25% paid by the farmer or through in-kind contributions. Administered by the Division of Soil and Water Conservation, the program provides funding to all 96 districts, offering up to $75,000 annually—or up to 90% coverage, capped at $90,000, for beginning or limited-resource farmers. 5. Educational Programs • NHSWCD educates the community on stormwater pollution and facilitates BMP installations to reduce runoff and prevent pollutants from entering waterways. By implementing BMPs like rain gardens, cisterns, and pervious pavement, residents can help manage stormwater and protect local water quality. Low Impact Development Low Impact Development (LID) refers to systems and practices that mimic natural processes to manage stormwater, protecting water quality and aquatic habitats. LID integrates natural areas that provide flood protection, cleaner air, and water. At both the site and regional levels, LID aims to preserve, restore, and create green spaces using soil, vegetation, and rainwater harvesting techniques. LID approaches land development (or redevelopment) by working with nature to manage stormwater at its source. It emphasizes preserving and recreating natural features, minimizing impervious surfaces, and designing functional, appealing drainage systems. LID treats stormwater as a resource, not a waste product, through practices like bioretention facilities, rain gardens, vegetated rooftops, rain barrels, and permeable pavements. Challenges with Low Impact Development LID practices, such as rain gardens and permeable pavements, are typically designed for managing smaller volumes of water, and may struggle to handle large storm events or high runoff, leading to overflow or failure. Factors like limited infiltration rates due to soil type, compacted soils, and space constraints in urban areas can exacerbate this issue. In densely developed spaces, the lack of available area for larger systems, like detention basins, complicates effective water management. Additionally, LID systems require ongoing maintenance, New Hanover County Stormwater Technical Report 7 and over time, clogging or material degradation can reduce their effectiveness. Integrating LID with traditional infrastructure can also be challenging, especially in retrofitted urban environments, while increasingly frequent extreme weather events may demand upgrades to handle larger volumes. Finally, implementing LID on a large scale can be costly and complex, particularly when trying to manage high runoff volumes across extensive urban areas. Low Impact Development Guidance Manual While large scale LID may not move larger volumes of water as efficiently as gray stormwater systems, it is not without its merit for small scale projects or for installation on residential properties. The Low Impact Development (LID) Guidance Manual for New Hanover County and the City of Wilmington provides a comprehensive framework for implementing LID strategies as an alternative approach to traditional stormwater management. This manual aims to assist developers, engineers, and planners in integrating Low Impact Development (LID) principles into urban and residential projects. It identifies regulatory barriers by reviewing existing ordinances and offers technical guidance on suitable LID technologies for coastal applications. The manual emphasizes stakeholder collaboration, including public-private partnerships, to promote sustainable stormwater management. It covers site planning, design principles for coastal environments, and techniques like bioretention, permeable pavement, and rainwater catchment systems, with case studies showing successful applications in urban retrofitting. The manual also presents detailed information on various stormwater best management practices (BMPs), such as tree box filters, green roofs, and stormwater wetlands, including their design criteria, performance, and maintenance. Practical guidance is provided on implementing LID, with recommendations for construction sequencing, erosion control, and long-term maintenance. Additionally, it highlights the importance of public education and community engagement in stormwater initiatives, while offering resources like a plant list and sample maintenance agreements. LID in Practice Low Impact Development (LID) stormwater systems are ideal for situations where the goal is to manage stormwater sustainably by mimicking natural hydrological processes, reducing runoff, and improving water quality. LID is particularly useful in new developments, redevelopment areas, urban or suburban settings with high impervious surfaces and flood-prone areas. It is also effective in sensitive watersheds where it helps reduce pollutants entering water bodies, as well as in sites with limited space, where traditional infrastructure may not be feasible. LID techniques are valuable in locations with high infiltration potential and in projects where the goal is to use more sustainable techniques. These systems are not only effective in reducing runoff and replenishing local aquifers but also help mitigate the urban heat island effect. They contribute to improving water quality, and reducing flooding, making them an essential tool for stormwater management.