STANDARD FOR RIPRAP AND CONDUIT OUTLET
PROTECTION
HOW MUCH OF A DIFFERENCE DOES THIS
CHANGE MAKE ?
Lets look at an example:
Q25 = 20.00 cfs, WO = 24 Inch or 2.00 ft.
TW = 0.2 x DO =0.2 x 2.0 ft.= 0.40 ft., q =20.00 cfs / 2.00 ft. =
10.00 sfs
Old Equation: D50 = 0.016 x q1.33 =0.016 x 10.001.33 = 0.855 ft.
TW
0.40 ft.
New Equation: D50 = 0.020 x q1.33 =0.020 x 10.001.33 = 1.069 ft.
TW
0.40 ft.
1.069 ft. = 1.25 = 25% Increase in D50
0.855 ft.
PREFORMED SCOUR HOLE SECTION HAS BEEN
REARRANGED TO “FLOW” MORE LOGICALLY
HORIZONTAL APRON SECTION HAS BEEN
REARRANGED TO “FLOW” MORE LOGICALLY
0.5
DO
ISHBASH CURVE – CHANNEL RIPRAP
ISHBASH EQUATION
Vc is not the velocity correlated with Minimum Specific Energy !
FIGURE TS14C–6 GRAPHICAL SOLUTION FOR ISBASH
TECHNIQUE FOR DIFFERENT STONE DENSITY
DIFFERENT STONE DENSITY
AVAILABLE FOR VERY HIGH VELOCITY
CIRCUMSTANCES
LANE METHOD – CHANNEL RIPRAP
RIPRAP QUESTIONS ?