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There shall be no net increase in peak stormwater runoff flow leaving a development from predevelopment conditions for the one-year design storm. New developments are required to minimize damage to subject streams caused by storm flows.
(A) Calculation of Peak Flow
Acceptable methodologies for computing pre- and post-development conditions for the one-year design storm include:
(1) The Rational Method (used when the drainage area is 200 acres or less)
(2) The Peak Discharge Method as described in USDA Technical Release Number 55 (TR-55) (drainage area is 2,000 acres or less)
(3) The Putnam Method (drainage area is greater than 2,000 acres)
(4) USGS Regression Equations, where applicable
The same method must be used for both the pre- and post-development conditions.
(B) Exceptions to Peak Flow Control
Developments with less than ten percent net increase in peak flow are not required to control peak flow from the site. However, if the net increase in peak flow from the new development is greater than ten percent, the entire net increase from pre-development peak flow must be controlled.
Cary, NC Land Development Ordinance On-line VIC Version - This site last updated 3/4/2008
Note: This is not the official version of the Cary Land Development Ordinance