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5 <br /> BIOFILTRATION. A stormwater quality and quantity BMP that utilizes vegetation <br />and soil to filter and absorb pollutants including nutrients, hydrocarbons and metals and <br />remove water volume through evapotranspiration. A bioretention practice in which an <br />underdrain is used. Typically, most of the water entering the biofiltration practice enters <br />the underdrain and is returned to the stormwater system, but some water infiltrates <br />(unless the BMP has an impermeable liner) or evapotranspires. The underdrain may be <br />at or elevated above the bottom of the practice (i.e. at the media-soil interface). <br /> BIORETENTION. A soil and plant-based stormwater management best <br />management practice (BMP) used to filter runoff. <br /> BRIDGE. A road, path, railroad or utility crossing over a waterbody, wetland, ditch, <br />ravine, road, railroad or other obstacle. <br /> BRIDGE SPAN. The clear span between the inside surfaces of a bridge's terminal <br />supports. <br /> CHANNEL. A perceptible natural or artificial depression, with a defined bed and <br />banks that confine and conduct water flowing either continuously or periodically. <br /> CONSTRUCTION ACTIVITY. Activities including clearing, grading, and excavating, <br />that result in land disturbance of equal to or greater than one acre, including the <br />disturbance of less than one acre of total land area that is part of a larger common plan <br />of development or sale if the larger common plan will ultimately disturb equal to or <br />greater than one acre. This includes a disturbance to the land that results in a change in <br />the topography, existing soil cover, (both vegetative and nonvegetative), or the existing <br />soil topography that may result in accelerated stormwater runoff that may lead to soil <br />erosion and movement of sediment. Construction activity does not include a disturbance <br />to the land of less than five acres for the purpose of routine maintenance performed to <br />maintain the original line and grade, hydraulic capacity, and original purpose of the <br />facility. Routine maintenance does not include activities such as repairs, replacement <br />and other types of non-routine maintenance. Pavement rehabilitation that does not <br />disturb the underlying soils (e.g., mill and overlay projects) is not construction activity. <br />. Includes construction activity as defined in 40 C.F.R. pt. 122.26(b)(14)(x) and small <br />construction activity as defined in 40 C.F.R. pt. 122.26(b)(15). This includes a <br />disturbance to the land that results in a change in the topography, existing soil cover <br />(both vegetative and non-vegetative), or the existing soil topography that may result in <br />accelerated stormwater runoff, leading to soil erosion and movement of sediment into <br />surface waters or drainage systems. Examples of CONSTRUCTION ACTIVITY may <br />include clearing, grading, filling, and excavating. CONSTRUCTION ACTIVITY includes <br />the disturbance of less than one acre of total land area that is a part of a larger common <br />plan of development or sale if the larger common plan will ultimately disturb one acre or <br />more. <br /> CONVEYANCE SYSTEM. Open channel, pipe or tile that is not a Public Drainage <br />System. A portion of a conveyance system is defined as “regional” if it carries flows from <br />a drainage area of greater than 200 acres. <br /> CRITICAL DURATION FLOOD EVENT. The 100-year precipitation or snow melt <br />event with a duration resulting in the maximum 100-year return period water surface