Quantity of stone in launching aprons of guide bank/Groyne/Revetment

Design of launching apron for revetment/guide bank shank/U/S shank of spur
Design data
Q.         =20000 Cumecs
f.          = o.96
V.        = 3 m/s
HFL.   = 100 m
LWL.  =  92 m
Bed RL=91m
Ss.       = 2.65
Protection slope 2:1
Design as per guidelines of BIS Codes
Size of stone for pitching.                     Ds = 0.25m
Thickness of pitching                           "t " = 0.50 m
Lacey's scouring depth.                        D.  = 13.015 m
Max. Designed scouring depth 1.5D.         = 19.523 m  & R L = 80.477 m
Apron laying level.                                     = 91 m
Des.scouring depth for apron.      Dmax    = 91 - 80.477 = 10.523 m

Thickness of launhing apron 1.25 to1.5 t.  = 0.625 to 0.75 m.  (for loose stones)
Launching slope of loose stone.                 = 2:1
Qty.of stone per mtr.of apron.                    =5^1/2 * t * Dmax
                                                                   =14.706 to 17.648 Cum/ m
Width of apron to be laid.                         = 1.5 * Dmax = 15.785 m
Av. thickness of apron                        "T"= 0.932 to 1.118 m
Thicness of apron at toe of pitching.        = 0.8 T.  
-------do-------------- river side end.          = 1.2 T
Aprons of loose stone boulders are to be laid in Wedge shape as per guidelines of IS-14262 & 10751