15A NCAC 02H .1062      MDC FOR DRY PONDS

The purpose of this Rule is to set forth the design requirements for dry ponds that are constructed to meet the requirements of this Section. 

(1)           SEPARATION FROM THE SHWT.  The lowest point of the dry pond shall be a minimum of six inches above the SHWT.  

(2)           TEMPORARY POOL DEPTH.  The maximum depth of the temporary pool shall be 10 feet. 

(3)           UNIFORM GRADING AND POSITIVE DRAINAGE.  The bottom of the dry pond shall be graded uniformly to flow toward the outlet structure without low or high spots other than an optional low flow channel.

(4)           LOCATION OF INLET(S) AND OUTLET.  The inlet(s) and outlet shall be located in a manner that avoids short circuiting.

(5)           PRETREATMENT.  Pretreatment devices shall be provided to settle sediment and prevent erosion.  Pretreatment devices may include measures such as gravel verges, filter strips, grassed swales, and forebays.

(6)           DRAWDOWN TIME.  The design volume shall draw down between two and five days. 

(7)           PROTECTION OF THE RECEIVING STREAM.  The dry pond shall discharge the runoff from the one-year, 24-hour storm in a manner that minimizes hydrologic impacts to the receiving channel. 

(8)           OUTLET.  The dry pond shall include a small permanent pool near the outlet orifice to reduce clogging and keep floating debris away from the orifice. A screen or other device shall be provided to prevent large debris from entering the outlet system.

(9)           VEGETATION.  The dam structure, including the front and back embankment slopes, shall be planted with non-clumping turf grass, and trees and woody shrubs shall not be allowed.   

History Note:        Authority G.S. 143-214.7B; 143-215.1; 143-215.3(a);

Eff. January 1, 2017.