§ 1-23. General.

A.

Determination of flooding and channel erosion impacts to receiving streams due to land-disturbing activities shall be measured at each point of discharge from the land disturbance and such determination shall include any runoff from the balance of the watershed that also contributes to that point of discharge.

B.

The specified design storms shall be defined as a twenty-four-hour storm using the NOAA Type "C" twenty-four-hour, twenty-five-year rainfall distribution recommended by the U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) when using NRCS methods or as the storm of critical duration that produces the greatest required storage volume at the site.

C.

For purposes of computing runoff, all pervious lands in the site shall be assumed prior to development to be in good condition (if the lands are pastures, lawns, or parks), with good cover (if the lands are woods), or with conservation treatment (if the lands are cultivated); regardless of conditions existing at the time of computation.

D.

Construction of stormwater management facilities or modifications to channels shall comply with all applicable laws, regulations, and ordinances. Evidence of approval of all necessary permits shall be presented.

E.

Impounding structures that are not covered by the Impounding Structure Regulations (4VAC50-20) shall be engineered for structural integrity during the 100-year storm event.

F.

Predevelopment and postdevelopment runoff rates shall be verified by calculations that are consistent with good engineering practices.

G.

Outflows from a stormwater management facility or stormwater conveyance system shall be discharged to an adequate channel.

H.

Proposed residential, commercial or industrial subdivisions shall apply these stormwater management criteria to the land disturbance as a whole. Individual lots in new subdivisions shall not be considered separate land-disturbing activities, but rather the entire subdivision shall be considered a single land development project. Hydrologic parameters shall reflect the ultimate land disturbance shall be used in all engineering calculations.

I.

All stormwater management facilities shall have an inspection and maintenance plan that identifies the owner and the responsible party for carrying out the inspection and maintenance plan.

J.

Construction of stormwater management impoundment structures within a Federal Emergency Management Agency (FEMA) designated 100-year floodplain shall be avoided to the extent possible. When this is unavoidable, all stormwater management facility construction shall be in compliance with all applicable regulations under the National Flood Insurance Program, 44CFR Part 59.

K.

Natural channel characteristics shall be preserved to the maximum extent practicable.

L.

Land-disturbing activities shall comply with the Virginia Erosion and Sediment Control Law and attendant regulations.

M.

Flood control and stormwater management facilities that drain or treat water from multiple development projects or from a significant portion of a watershed may be allowed in resource protection areas defined in the Chesapeake Bay Preservation Act provided such facilities are allowed and constructed in accordance with the Stormwater Management Act and this chapter, and provided that (i) the local government has conclusively established that the location of the facility within the resource protection area is the optimum location; (ii) the size of the facility is the minimum necessary to provide necessary flood control, stormwater treatment, or both; (iii) the facility must be consistent with a comprehensive stormwater management plan developed and approved in accordance with Section 1-19 or with a VSMP that has been approved prior to July 1, 2012, by the board, the Chesapeake Bay Local Assistance Board prior to its abolishment on July 1, 2012, or the Board of Conservation and Recreation; (iv) all applicable permits for construction in state or federal waters must be obtained from the appropriate state and federal agencies, such as the U.S. Army Corps of Engineers, the Virginia Department of Environmental Quality, and the Virginia Marine Resources Commission; (v) approval must be received from the local government prior to construction; and (vi) routine maintenance is allowed to be performed on such facilities to assure that they continue to function as designed. It is not the intent of this subdivision to allow a best management practice that collects and treats runoff from only an individual lot or some portion of the lot to be located within a resource protection area.

(Ord. No. 3337, 4-22-14, eff. 7-1-14; Ord. No. 3618, 6-16-20)

(Ord. No. 3337, 4-22-14, eff. 7-1-14; Ord. No. 3618, 6-16-20)