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| Acknowledgements


In 2013, the Town of Nags Head began work with the N.C. Coastal Federation to develop a Low Impact Development manual as a reference document for local citizens and developers as part of Town efforts to improve stormwater management and as a technical resource for application of Town Stormwater regulations. This project is based on the LID manual for the coastal towns of Columbia, Cedar Point and Cape Carteret. The Town of Columbia worked in direct partnership with the N.C. Coastal Federation to complete an LID manual. The Town of Cedar Point worked in partnership with the Town of Cape Carteret, the N.C. Coastal Federation, engineering consultants Withers & Ravenel, N.C. Division of Water Quality and the LID Technical Review Team to complete the Cedar Point/Cape Carteret manual. We would like to thank these three communities and their partners for sharing their work and providing a model for us to follow. At the local level, the following people were involved in the development and review of the updated Stormwater Regulations which are referred to in this manual as well as for several exhibits provided.


Town Ordinance Update Committee

Marvin Demers

Richard Murphy

Pogie Worsley

Mark Cornwell

Bob Edwards

Kelly Wyatt, CZO

Dabni Shelton, CZO

Kim Allen

Andy Deel, P.E

David Ryan, P.E.

Elizabeth Teague, AICP, CTP





Town of Nags Head Board of Commissioners

2012-13

Mayor Bob Oakes

Mayor Pro-Tem Doug Remaley

Commissioner Susie Walters

Commissioner Renee Cahoon

Commissioner Anna Sadler



2013-14

Mayor Robert Edwards

Mayor Pro-Tem Susie Walters

Commissioner Renee Cahoon

Commissioner Marvin Demers

Commissioner John Ratzenberger


Town of Nags Head Planning Board

Marvin Demers

Richard Murphy

Pogie Worsley

Mark Cornwell

Bob Edwards

Barbara Gernat

Clyde Futrell

Toni Parker
Special thanks go to David Ryan, P.E., Andy Deel, P.E., and the North Carolina Coastal Federation staff for their contributions to this Manual.  UNC Chapel Hill Outer Banks Field Site interns Mark Stripp and Katrina Phillips contributed the photographs.

| TABLE OF CONTENTS





  1. Background and Purpose




  1. Practices to Manage Stormwater Fact Sheets




  1. General Siting Considerations related to Separation Distances




  1. Using LID to Comply with Town Stormwater Management Requirements

Application Requirements


Residential BMP Selection Guide for Non-Engineered BMP'S

(For projects using fill amounts of greater than 1’ and less than 2')


Residential BMP Selection guide for Engineered BMP'S

(For fill amounts of greater than 2')

And Commercial/Multi-Family BMP Selection guide for Engineered BMP'S


  1. Reference Information

Glossary


Sources

Town of Nags Head

P.O. Box 99

Nags Head, NC 27959

North Carolina Coastal Federation

Northeast Office

128 Grenville Street

Manteo, NC 27954




  1. Background and Purpose




This manual is a guide for property owners who want to improve stormwater management on their site and for those who seek low cost practices to achieve compliance with the Town of Nags Head Stormwater Ordinance, Chapter 34 of the Town Code of Ordinances. Because we all play a role in protecting coastal waters, everyone can use the solutions described, not just those requiring permits. In so doing, everyone can help protect water quality and reduce the potential for localized flooding.
| What is stormwater runoff?
Stormwater run-off is precipitation shed off the ground or impervious surfaces. When rain reaches the ground, it infiltrates into the soil until the soil is saturated. This process naturally filters the water before it settles into aquifers or makes its way as groundwater to estuaries, the sound, or the ocean. The sandy soils of the Outer Banks generally absorb rainfall efficiently into the ground. However, some periods of rainfall may exceed the ground’s ability to collect and filter the water. Precipitation onto saturated ground can result in localized flooding.
Residential and commercial development can alter natural drainage patterns and increases impervious surfaces such as parking lots, driveways or rooftops which do not absorb water. Development activities which result in the removal of trees and other vegetation can effectively reduce natural passive stormwater measures such as evapotranspiration, (plant uptake). This can result in less precipitation being absorbed into the ground or used by plants and increasing the potential for runoff being conveyed off-site.


Rainfall runoff can collect pollutants which are discharged to the bodies of water that we depend on for food, income and recreation. As rain hits a surface, the runoff collects chemicals, oil, antifreeze and refuse from parking lots, or fertilizers, pesticides, and sediment from lawns and gardens. Run-off can also pick up loose soil or scour the ground, producing erosion. Sediment and silt carried by stormwater can impede drainage flow resulting in reduced system effectiveness.




| What Is Low Impact Development?


This manual focuses on Low Impact Development or “LID” approaches to managing stormwater. The goal of LID is to mimic the natural hydrological function of the landscape on any given site.
LID uses techniques to capture and store stormwater as close to the source as possible to promote infiltration and treatment, thereby reducing runoff and the amount of pollution that runoff can convey. LID practices include site planning that provides small, decentralized management practices and approaches that are versatile and site specific.
Unlike conventional strategies that treat stormwater as a secondary component of design, LID incorporates the natural slope, soils and hydrology as a framework for development design.
For new development, an LID approach identifies natural features and strategically places buildings, driveways and parking areas advantageously to allow for a stormwater management system that works with existing natural features and drainages.
In redevelopment, LID includes forming an inventory of built and un-built areas and incorporating strategies and technologies to handle existing conditions and maximize infiltration in existing open space. The cumulative impact of retrofitting techniques can have a significant impact.
The desired result is a functional landscape that generates less runoff, less pollution, less erosion and less overall damage to coastal waters. The attention to natural hydrology and integrated use of open space and vegetation, also results in attractive, multi-functional landscapes.


Key Principles in Low Impact Development:



  1. Focus on Prevention.

  • Protect wetlands, floodplains and coastal habitats.

  • Maintain slopes and flow paths.

  • Minimize grading and tree clearing.



  1. Work with the Landscape.

    • Identify environmentally sensitive areas.

    • Outline a plan to protect those areas.

    • Use hydrologic features of the site.




  1. Keep it Simple.

    • Use low-cost approaches to decentralize run-off

    • Micromanage stormwater close to where it falls

    • Direct run-off from impervious surfaces to landscaped areas and other small scaled techniques for infiltration.




  1. Practice multi-tasking.

  • Use landscaping for a variety of purposes. Landscapes can capture and treat pollutants and provide curb appeal.

  • Distribute management practices on a site so that they work together to reduce run-off and run-off impacts.




  1. Maintain and Sustain

  • Maintain LID features so that they remain effective and provide long-term success.



| What is a Best Management Practice or BMP?


Best Management Practices or “BMPs,” are inter-changeable terms which describe the techniques implemented to treat or limit pollutants and other damaging effects of stormwater runoff. In North Carolina, these terms are used to describe the techniques implemented in order to meet legislative and North Carolina Administrative Code requirements. The North Carolina Stormwater Best Management Practices Manual or “NCDENR BMP Manual” is the stormwater design manual approved by the North Carolina Division of Energy, Mineral and Land Resources. This document is designed to be a local version of a BMP Manual, providing guidance for practices which can be utilized effectively in the Nags Head environment and to meet the Town’s Stormwater Management requirements.
The term best management practice or BMP encompasses two major categories of BMPs: non-structural and structural. Non-structural BMPs are typically passive or programmatic and tend to focus on source control and pollution prevention; reducing pollution in runoff by reducing the opportunity for the stormwater runoff to become concentrated and exposed to pollutants. Structural BMPs refer to physical structures designed to remove pollutants from stormwater runoff, reduce downstream erosion, provide flood control, and promote groundwater recharge.
| How To Use This Manual:
This Manual provides information in three major areas.


  1. Chapters 2 and 3 of this Manual offer a variety of LID “Best Management Practices” (also called “BMPs”) and considerations to keep in mind when choosing which types of practices for different sites. With this guidance, anyone can incorporate one or more practices into their site for improved stormwater management, both in new development and in re-use of existing developed sites. Practices are described in Chapter 2 with Fact Sheets which are intended for easy reference and to be used individually or together to create a stormwater management strategy for a given project. Each Fact Sheet contains a brief overview of the LID technique, its benefits, information on installation and maintenance, and reference information. Chapter 3 provides additional information on siting the BMP relative to maintaining required distances from septic systems and wetlands.




  1. Chapter 4 of the Manual is an overview of the Town’s application requirements for those who have to comply with the Town’s Stormwater Management Ordinance, Chapter 34 of the Town’s Code of Ordinances. These requirements apply to commercial and multi-family projects and for individual sites of residential development that use fill. While LID techniques are applicable to commercial projects, this Manual will be particularly helpful for individual residential lot development and lays out a step by step approach for developing a stormwater management plan that will comply. Residential development that does not use fill in excess of 12” in depth, lot disturbance limited to site investigations (for the purpose of surveying or determining septic suitability), and land disturbance and fill used in the repair and/or replacement of existing septic systems, are exempt from the Town’s stormwater management requirements, but can still benefit from applying LID techniques.




  1. Chapter 5 of the Manual provides reference material regarding the Nags Head environment, soil types, and other useful information. This section also includes sources for additional information and application forms.

Questions regarding this Manual or the Town’s development requirements should be directed to the Town of Nags Head Planning and Development Department, located at 5401 South Croatan Highway in Nags Head, NC, 27959, (252) 441-7016.


In addition to this Manual, the following are also useful references:


The North Carolina Manual for Stormwater Best Management Practices, available at the NC Division of Water Resources (NCDWR): http://portal.ncdenr.org/web/lr/bmp-manual
The Low Impact Development Guidebook by NC State University, available at: http://www.ces.ncsu.edu/depts/agecon/WECO/lidguidebook/

Stormwater Best Management Practices by the US EPA, available at: http://water.epa.gov/polwaste/npdes/swbmp/



2. Best Management Practices

| Site Fingerprinting






What Is Site Fingerprinting?

-Site Fingerprinting is a practice that uses site design as a stormwater management tool by reducing land disturbance, preserving soil structure, and utilizing suitable natural areas (rather than expensive structural practices for runoff management).

-Rather than grading land to fit a desired development type, the type of development is dictated by the existing conditions of the site, resulting in a developed site which uses the land to maintain and protect the natural balance of the surrounding ecosystem.
Did You Know?

-Site Fingerprinting can be done during the planning process for no additional cost and can often lead to reduced infrastructure costs.

-By fitting the development to the land, it is often easier to preserve existing vegetation, giving a more established look to new developments.

-A little preservation goes a long way toward effective stormwater management.
Benefits

  • Reduced stormwater runoff volumes discharged into our waterways

  • Maintained natural drainage patterns

  • Reduced infrastructure costs

  • Healthier green space


Helpful Hints

When trying to preserve the health of the local watershed, the best place to start is to enhance and preserve the natural stormwater treatment areas. These include marshes, wetlands, and coastal forests, which have great potential to control and treat stormwater runoff.






Where to Start

  1. Start by identifying the natural characteristics of a site. Conduct “natural resources inventory” of what’s already there.

  • Wetlands

  • Shoreline

  • Floodplain

  • Forests

  • Flow patterns

  • Depressions and natural low areas




  1. Determine site potential for LID stormwater treatment.

  • Locate development on the least sensitive natural areas

  • Protect the preservation areas during construction

  • Use density where appropriate

  • Minimize soil compaction during construction

  • Use disconnected impervious areas to minimize runoff volumes

  • Use the natural drainage patterns


References and Resources for Site Fingerprinting

Low Impact Development Center: www.lowimpactdevelopment.org

Green Growth Guidelines, Chapters 1-6, Site Fingerprinting Utilizing GIS/GPS Technology: http://coastalgadnr.org/cm/green/guide

Urban Land Institute: http://www.uli.org/wp-content/uploads/2012/07/EnvironmentandDev.ashx.pdf

American Institute of Certified Planners (AICP): www.planning.org - search stormwater

American Society of Landscape Architects (ASLA): www.asla.org - search LID

Ladybird Johnson Wildflower Center: http://www.wildflower.org/- search LID








| Disconnected Impervious Surfaces





What is a Disconnected Impervious Surface?

-Roof tops, parking lots, and other impervious surfaces often drain directly to pipe systems or ditches, increasing runoff and preventing rainwater from soaking into the ground.

-Disconnected impervious areas are those which divert or direct stormwater to naturally vegetated areas.

-This reduces pollution by slowing down the runoff, increasing infiltration, and filtering flow through vegetation.
Did You Know?

-During small storms, disconnected impervious areas can reduce runoff volume by 30% to 100%.

-This technique also reduces the need for irrigation, and lowers infrastructure costs.

-This approach spreads multiple practices throughout a site, as opposed to the costs and maintenance problems associated with one large retention pond.


Benefits

  • Reduces stormwater runoff volumes discharged into our waterways




  • Reduces infrastructure costs




  • Reduces dependence on irrigation




  • Provides healthier green space




  • Can provide a distributed regime which diffuses runoff and pollutant concentration.


Helpful Hints

-For the best effect, tie multiple practices together, using disconnected impervious areas as part of a larger stormwater management strategy.


Where to Start

  1. As a retrofit, see if it’s possible to add curb cuts in the edge of existing parking lots to allow runoff to flow into vegetated areas.

  2. On new or re-development sites, try to slope the parking lots, roofs, and sidewalks into landscaped areas, open spaces, or woods.

  3. Use rip-rap or concrete or other material to create edging to prevent erosion.

  4. Make sure water is directed away from buildings.

  5. Disconnect the building downspouts (See Simple Solutions Sheets) and develop landscaped areas along the drip line to diffuse roof runoff.


References and Resources

See the “Simple Solutions: Downspout Disconnection” sheet for more help. Contact your local nursery or Town staff for more assistance.

NC Cooperative Extension: www.ces.ncsu.edu

search impact solutions

Low Impact Development Center: www.lowimpactdevelopment.org

NC Coastal Federation: www.nccoast.org

search for disconnected impervious surfaces








| Planter Boxes

What is a Planter Box?

-Planter boxes use soil with high flow rates of filtration. Soil media can control and treat runoff. Runoff flows through the sandy soil mix, which traps solids and pollutants.

-Planter boxes use vegetation to help absorb the water trapped by the soil. The plants also create a mini ecosystem within the soil, fostering healthy microbes which aid in breaking down oil and grease.
Did You Know?

-Planter Boxes can be integrated into the existing storm drainage system with minimal disturbance, making them an excellent retrofit.

-Planter boxes provide treatment at the source in a small footprint.
Benefits


  • More trees, flowers, and shrubs reduce runoff volume and pollution.




  • Small footprint allows boxes to be easily integrated into sites and are great retrofits.




  • Planter boxes can be used to visually soften or create buffers in hardscape areas such as along parking lots or walkways.


Helpful Hints

-Use the planter box upstream of an underground BMP such as a cistern so that the water entering the device is cleaner.

-Holes in the bottom of the box increase filtration if underlying soil is suitable.

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images
Where to Start


  1. Location

-Site the planter box in the curb line, immediately upstream of a catch basin or inlet.

-Typical boxes are 3’ deep – make sure there is a suitable outfall to drain the box between storms.

-The box should be oriented so flow comes across inlet throat, not directly at inlet opening.

-Use plants that are native to coastal NC.





  1. Sizing

-The soil media should be at least 3’ deep.

-The minimum soil infiltration rate should

be 10” per hour or greater.


 

Max Impervious Area



Planter Box Size




(acres)

4' x 6'

0.14

4' x 8'

0.19

4' x 12'

0.28

6' x 6'

0.21

6' x 8'

0.28

6' x 10'

0.35

6' x 12'

0.42

7' x 13'

0.54







  1. Installation

-Contractor assistance will be required.

-Many manufactured systems are available, contact a manufacturer for specific installation guidelines.



References and Resources

Low Impact Development Center: www.lowimpactdevelopment.org; search planter box








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