1-year storm event - the amount of precipitation that will be equaled or exceeded by a storm event about once every year; determined based on historic rainfall data for a specific region

100-year storm event - the amount of precipitation that will be equaled or exceeded by a storm event about once every 100 years; determined based on historic rainfall data for a specific region

Albedo - the measure of a surface’s ability to reflect light

Curve number - a parameter that relates runoff characteristics to a site’s ground cover features

Extensive - refers to a green roof that has shallow soils; they typically feature drought-tolerant plant species and are less expensive that intensive green roofs

First flush effect - the principle that runoff occurring earlier in a storm is more contaminated because it carries away pollutants that have accumulated on impervious surfaces

Gap-graded - refers to aggregate in which the size of all pieces is intentionally uniform

Hydrograph - a plot commonly used to describe runoff; it displays time on the x-axis and flow rate on the y-axis

Integrated Management Practice (IMP’s) - any management technique used to maintain a site’s predevelopment hydrology; they are often scattered throughout a site to treat runoff on the microshed scale

Intensive - refers to a green roof that has deeper soils; they are able to support a wide range of native plant species and are more expensive than extensive green roofs

Riemann sum - a numerical integration technique that approximates the area under a curve as a series of rectangles with widths that are uniform and heights that are based on the values of the curve

Sedum - a genus of hardy, succulent plants that retain moisture well

Time of concentration - the time taken for water to travel the longest flow path in a watershed