Article XIII, Section 13-109

Other

• Channel protection storm for manmade conveyance

  The manmade stormwater conveyance shall convey the post-development peak flow rate from the two-year 24-hour storm event without causing erosion of the system.

• Channel protection storm for natural conveyance

  The maximum peak flow rate from the one-year 24-hour storm following the land-disturbing activity shall be calculated...

• Development review threshold within CBPA2,500 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.

  Any development, redevelopment, or use exceeding 2,500 square feet of land disturbance within the CBPA shall be subject to the development review process outlined in subsection (C) below prior to any clearing of the site, or the issuance of any building, land use, or land development permit.

• Flood protection storm

  Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following criteria as demonstrated by the use of acceptable hydrologic and hydraulic methodologies: ... ten-year 24-hour storm event.

• Improvement factor for sites >1 acreacre43,560 square feet — about the size of an American football field without the end zones.0.8 dimensionless

  I.F (Improvement Factor) equals 0.8 for sites > 1 acre or 0.9 for sites ≤ 1 acre.

• Improvement factor for sites <=1 acreacre43,560 square feet — about the size of an American football field without the end zones.0.9 dimensionless

  I.F (Improvement Factor) equals 0.8 for sites > 1 acre or 0.9 for sites ≤ 1 acre.

• Water quality major impact assessment threshold5,000 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.

  A water quality major impact assessment is required for development or redevelopment within RPAs or under an exception that involves more than 5,000 square feet of land disturbance; or for any development or redevelopment within the RMA which involves more than 5,000 square feet of land disturbance adjacent to an RPA...

• Minimum phosphorus reduction for prior developed lands >=1 acreacre43,560 square feet — about the size of an American football field without the end zones.20 pct

  For land-disturbing activities disturbing greater than or equal to one acre that results in no net increase in impervious cover from the pre-development condition, the total phosphorus load shall be reduced at least 20 percent below the pre-development total phosphorus load.

• Minimum phosphorus reduction for prior developed lands <1 acreacre43,560 square feet — about the size of an American football field without the end zones.10 pct

  For regulated land-disturbing activities disturbing less than one acre that results in no net increase in impervious cover from the pre-development condition, the total phosphorus load shall be reduced at least ten percent below the predevelopment total phosphorus load.

• Minimum vegetated buffer width for intermittent streams/non-tidal wetlands50 ft

  A 50-foot wide vegetated area preserved where present, or established where not present, on the outward edge of these features shall be considered a sufficient BMP to meet this standard if the vegetated area is designed to prevent erosion and scouring.

• Water quality minor impact assessment threshold5,000 sqftsq ftSquare feet. An acre is 43,560 sq ft; a typical suburban lot is 7,000–10,000.

  A water quality minor impact assessment is required for development or redevelopment within RPAs or under an exception which involves 5,000 or less square feet of land disturbance; or for any development or redevelopment within the RMA that involves 5,000 or less square feet of land disturbance adjacent to an RPA...

• Steep slopeSteep slopeGround above a stated gradient, where building is restricted or barred. threshold for environmental site assessment15 pct

  Steep slopes greater than 15 percent in grade

• Alexandria water quality volume default treatment

  For new development and development on prior developed lands in subsections (4) and (5) above, the entire Alexandria water quality volume default from the site shall be treated, or the requirements must be met consistent with section 13-110.