Acknowledgements
Using LID to Comply with Town Requirements
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| 4. Using LID to Comply with Town Requirements
When is a stormwater plan required by the Town of Nags Head? The requirements to retain and treat stormwater on site are described in Chapter 34 of the Town’s Code of Ordinances.
Who can develop a stormwater plan? For a stormwater plan for a commercial, mixed-use or multi-lot development such as a subdivision, a designer shall be a qualified and registered design professional knowledgeable within the field of work for the performance of the design, construction, and operation and maintenance of what is being proposed. This could include someone qualified in engineering, landscape architecture, architecture or environmental design. Stormwater plans that include engineering, or those plans that utilized a height of fill greater than 2 feet from the existing or natural grade, must be sealed by a Practicing Engineer and will be reviewed by the Town Engineer. For a stormwater plan for a single-family residential application where proposed fill amounts are greater than 1’ do not exceed 2’ in height from the pre-development surface grades, then the design may be submitted by anyone, including those who are not registered design professionals or engineers, as long as the plan follows the guidelines for management practices provided in this manual. The goal is to allow smaller scale projects to be developed with minimal up-front costs through the implementation of LID approaches outlined in this Manual. For example, the design of swales must follow the specifications laid out in Table A. The design of rain gardens must follow the specifications of Table B. Stormwater Plans developed under this approached will be reviewed by Town staff certified in LID. Stormwater plans submitted are not required restricted to the management methods described within this manual; however, the methods, calculations, tables, figures, and procedures outlined in this manual as well as the NC BMP Manual will be used to review and issue decisions concerning proposed BMP’s for compliance with Sections 34-5 through 34-7 of the Code of Ordinances, and alternative designs will need to show reasoning behind proposals and to indicate equal or better performance for the BMP’s included in this Manual. What are the steps to developing an effective stormwater plan under the Town Ordinance?
| Glossary Annual plant - A plant that completes its entire life cycle in a single growing season. Base flow – The flow in a stream between storm events. The flow is supplied by groundwater. Best Management Practice (BMP) – A practice or combination of practices that are the most effective and practicable means of controlling pollutants at levels compatible with environmental quality goals. Bioretention Area – A water quality practice that utilizes landscaping and soils to treat stormwater by collecting it in shallow depressions and then filtering it through a planting soil media. (Also see rain garden.) Buffer - An area of trees, shrubs and plants next to a waterbody designed to protect the receiving waterbody from sediment and pollutants contained in storm water runoff. Buffers also function as habitat for migratory birds and aquatic and terrestrial wildlife. Check dam - A small barrier built across the direction of water flow in a swale to retain excess water during heavy rains and to slow the speed of runoff traveling through the swale. Deciduous plant - A plant that sheds or loses its foliage at the end of each growing season. Disconnected Impervious Surfaces - Integration of treatment and management measures into developed areas to remove the links between hardscaped areas such as driveways, walkways, parking areas with the strategic placement of distributed lot-level controls that can be customized to more closely mimic a watershed’s hydrology. Ecosystem – An interactive system that includes the organisms of a natural community together with their abiotic, physical, chemical and geochemical environment. Easement - A right, such as a right-of-way, afforded a person to make limited use of another's real property. Estuary – Brackish-water area influenced by the tides where the mouth of the river meets the sea. Estuaries are breeding grounds for many species of fish and shellfish. Evergreen plant - A plant that remains green and retains its foliage throughout the year. Fecal coliform bacteria – Bacteria that are present in the intestines or feces of warm-blooded animals. Often used as indicators of water quality. Floodplain – Areas that are periodically flooded by lateral overflow, such as river. Forebay – Stormwater design feature that uses a small basin to settle out incoming sediment delivered in runoff to a stormwater BMP. Geographic information systems (GIS) – A computer system for capturing, storing, checking, integrating, manipulating, analyzing and displaying data related to positions on the Earth’s surface. Typically, GIS is used for handling maps of one kind or another. These might be represented as several different layers where each layer holds data about a particular kind of feature (i.e. roads, waterbodies, etc.). Each feature is linked to a position on the graphical image of a map. Groundwater - Water below the earth’s surface, often between saturated soil and rock, that supplies drinking wells and springs. Runoff can seep into the soil and recharge groundwater supplies. Habitat - The specific area or environment where a plant or animal lives. A habitat must provide all of the basic requirements for life (food, water, shelter) and should be free of harmful contaminants and pollution. Hydrology – The science of dealing with properties, distribution and circulation of water. Impervious surface - Any surface that water cannot penetrate into (i.e. parking lots, streets, sidewalks, rooftops). Infiltration - the slow passage of rainwater through the soil. Low Impact Development - 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. LID's goal is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source Native plant – A plant that naturally occurred in an area before disturbance by humans. Native plants are adapted to the weather, temperature and soil conditions of this region. Native plants require less (if any) fertilizers, pesticides or irrigation and tend to be disease and drought-tolerant. Nonpoint source pollution (NPS) - Pollution that comes from many different sources in a watershed and is carried by storm water runoff into local waterways. Sources of NPS pollution are difficult to identify and control. Typical NPS pollutants are pet waste, lawn fertilizer, pesticides, car washing detergents, litter and sediment. Nutrient – A primary element necessary for the growth of living organisms. For example, nitrogen and phosphorous, are nutrients required for phytoplankton (algae) growth. Outfall – Point where water flows from a conduit, stream, pipe, drain, etc. Perennial plant - A plant that grows and persists for more than one year. Perennial plants persist as vegetation from year to year or re-sprout from their rootstock annually. Pervious materials - Pervious materials allow water to soak into the surface by virtue of their porous nature or by “void” spaces in the material. Pervious Paving - Water-pervious materials such as gravel, crushed stone, open paving blocks or pervious paving blocks for driveways, parking areas, walkways, and patios that minimize runoff from those areas, as well as increase infiltration. Point source pollution - Water pollution entering the environment from a single point (i.e. factory pipe). Pollution - Any substance that exists in the environment that is undesirable or harmful for that environment. Rain Garden – A rain garden is a shallow depression planted with native plants, flowers or grass that captures and infiltrates rain before it becomes polluted runoff. Receiving waters – Creeks, streams, rivers, lakes, estuaries and other bodies of water into which stormwater flows into. River Basin - A river basin is the land that water flows across or under on its way to a river. As a bathtub catches all the water that falls within its sides, a river basin sends all the water falling on the surrounding land into a central river and out to an estuary or the sea. Runoff Volume - The total volume of runoff is the amount of water that flows through the hydrometrically closed segment of a drainage basin. The total volume of runoff is usually determined graphically by constructing a hydrograph, that is, a diagram of change over time (t) of discharge (Q) for a year. Using the hydrograph it is possible to construct the integral curve of runoff, which gives a representation of the progressive accumulation of water volume (in a reservoir) with the passage of time. The modulus of runoff is the volume of runoff in a unit of time per unit of area of the watershed; it is usually expressed in //sec-km2 or //sec-hectare. Sediment - Soil or dirt that washes into a body of water and contributes additional nutrients to the water. Sediment often comes from construction sites or bare lawns. Storm drainage system - The system built to collect and transport runoff to prevent flooding. This system consists of storm drains, drainage ditches, pipes and culverts. Anything that flows into the storm drainage system flows directly into local creeks and waterways. (Stormwater runoff is not treated.) Storm drainage systems are completely separate from those that carry domestic and commercial wastewater (sanitary sewer system). Stormwater runoff – When rain falls on surfaces such as rooftops and parking lots it is not absorbed into the ground. Instead, it flows over these hard surfaces collecting pollutants along the way. This polluted stormwater runs into fragile coastal waters, degrading the health of creeks, rivers and sounds. Surface water – The water that rests on top of the earth in streams, lakes, rivers, oceans and reservoirs and is open to the atmosphere (i.e. rivers, lakes, creeks, streams, etc.). TMDL – Total maximum daily load of the amount of pollutants that can flow into the water without violating water-quality standards. Reductions are assigned to various sources. Tributary - A stream that flows into a larger stream or other body of water. Watershed - The land area that drains water to a particular stream, lake or river. Water quality – The biological, chemical and physical conditions of a waterbody; a measure of the ability of a waterbody to support beneficial uses. Wetland - Land whose soil is saturated with moisture either permanently or seasonally. They are generally distinguished from other water bodies or landforms based on their water level and on the types of plants that thrive within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough season each year to support aquatic plants. Sources - City of Wilmington Stormwater Services stormwater glossary, Dictionary.com, Low Impact Development Center, NC Coastal Federation Yüklə 183,6 Kb. Dostları ilə paylaş:
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