Analysis of Alternatives (AoA): an analytical comparison of the effectiveness, cost, and risks of any potential OCPs that could fit the site. Factors that go into this analysis include runoff volume, erosion, and other site-specific variables.

Best Management Practices (BMPs): a practice, or combination of practices, that is determined to be an effective and practicable (including technological, economic, and institutional considerations) means of preventing or reducing the amount of pollution generated by nonpoint sources to a level compatible with water quality goals.

Channel Protection Volume (CPv): The stormwater treatment standard that requires that stormwater from a given land use after a 1-year, 24-hour rainfall event be contained in a stormwater management structure for a certain amount of time before it enters the nearest water body. For cold water fish habitats, stormwater must be contained for 12 hours, and for warm water fish habitats, 24 hours, to meet the standard of channel protection volume.

Climate Resilience: The capacity for human communities and surrounding ecosystems to absorb stresses and maintain function in the face of external stresses imposed upon it by climate change (e.g., flooding, drought, etc).

Culvert: a tunnel carrying a stream or open drain under a road, railroad, trail, or similar obstruction/impervious surface.

Drainage area:  the total surface area, upstream of a point on a stream, where the water from rain, snowmelt, or irrigation which is not absorbed into the ground flows over the ground surface, back into streams, to finally reach that point.

Drainage Area Boundaries: Comparable to the rim of a bowl, drainage area boundaries are the higher elevation points surrounding an area from which water is shed and deposited into points of low elevation.

Erosion: The action of surface processes (e.g., water flow in this context) that remove soil, rock, or dissolved material from location and then transports it to another.  

Eutrophication: excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.

FEMA: The United States Federal Emergency Management Agency, which responds to natural disasters including extreme weather events.

FEMA floodplains: A floodplain is an area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding. FEMA has mapped floodplains by their definition and standards. These areas may differ from local boundaries.

Fluvial Erosion Hazard (FEH) Zones: Formal areas delineated for certain communities based on studies of how far the stream or river reaches during heavy rain/flood events.

Gully: A landform created by running water, eroding sharply into soil (typically on a hillside).

Headwaters: A tributary stream that is close to or forms a part of its source river.

Hydrologic soil group: A soil classification system created by the NRCS, ranked A to D. Group A consists of sand, loamy sands, or sandy loams, and has the lowest runoff potential and highest infiltration rates. Group B consists of silt loams or loams, and has a moderate infiltration rate. Group C consists of sandy clay loams, and have low infiltration rates. Group D consists of clay loams, silty clay loams, sandy clays, silty clays, or clays, and has the highest runoff potential and lowest infiltration rates.

Hydrology: The movement of water in relation to land.

Impervious surfaces: A surface (such as asphalt) that does not allow water to penetrate or infiltrate through.

Infiltration:  The downward movement of water into soil.

Non-point source pollution:  Pollution caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters and ground waters.

NRCS: The United States Department of Agriculture’s Natural Resource Conservation Service.

Optimal Conservation Practices (OCPs): Best Management Practices (BMPs) that are enhanced to account for climate adaptations and larger stormwater volumes.

Point source pollution:  Any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged.

Ponding: Areas where water forms pools or puddles.

Rill: A shallow channel cut into soil by the erosive action of flowing water.

Riparian Buffer: Vegetated areas along river banks that filter pollution, protect riverbank stability, and provide habitat.

River Corridor: Room needed by a stream to maintain its least-erosive form and buffer.

Runoff: The movement of water, and substances carried with it, across a land surface.

Stormwater runoff: Runoff generated from rain and snowmelt events that flow over land or impervious surfaces, such as paved streets, parking lots, and building rooftops, and does not soak into the ground.

Stormwater Infrastructure: the basic physical structures designed to capture, store, and treat stormwater runoff. Stormwater infrastructure includes (but is not limited to) retention ponds, ditches, swales, rain gardens, and constructed wetlands.

Riparian Buffer: Vegetated areas along river banks that filter pollution, protect riverbank stability, and provide habitat.

Watershed: a basin-like landform defined by highpoints and ridgelines that descend into lower elevations and stream valleys; the area of land that drains to a common outlet. Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers that drain into Lake Champlain.

Water Quality Volume (WQv) and Treatment Standards: The stormwater infrastructure must be designed to capture 90% of the annual storm events (referred to as the 90% rule), and remove 80% of the annual post-development total suspended solids load, and 40% of the total phosphorus load.

1-year, 24-hour storm: A storm volume that could be expected to hit Vermont any given year over a period of 24 hours (i.e., a 100% chance). Currently, the Vermont Stormwater Manual defines this as a roughly 2 inches of rainfall in 24 hours. This value varies slightly across the state. In Chittenden County, a 1-yr, 24-hr storm is defined as bearing 2.1 inches of rainfall.

10-year, 24-hour storm: A storm volume that could be expected to hit Vermont once every ten years over a period of 24 hours (i.e., a 10% chance). In Chittenden County, a 10-yr, 24-hr storm is defined as bearing 3.2 inches of rainfall.

100-year, 24-hour storm: A storm volume that could be expected to hit Vermont once every one- hundred years over a period of 24 hours (i.e., a 1% chance). In Chittenden County, a 1-yr, 24-hr storm is defined as bearing 5.2 inches of rainfall. Note: When considering climate change (think Tropical Storm Irene), 100-yr, 24-hr storms are projected to occur far more frequently than a 1% chance would suggest.