2012-01-17_REVISION - M2005050 ‎(2)‎

• Permit No: M2005050
• IBM Index Class Name: REVISION
• Doc Date: 1/17/2012
• Doc Name: SPILLWAY DESIGN DISCUSSIONS
• From: TIM CAZIER
• To: JAMES PIERCE
• Media Type: D
• Archive: No

Wherever riprap is used as a protective liner in an emergency spillway, a compacted and stabilized
earthen plug should be left in place (on the inner side of the spillway) to prevent water from discharging
through the emergency spillway until the design water elevation is reached (see Standard Construction
Detail #8).
WTE -I3 WW I _.
1
WCE
LRt-
V
SECT
EARTHEN P1
STANDARD CONSTRUCTION DETAIL #8
Sediment Basin Emergency Spillways
tMtfANKMtN I NILL I WIN ALUNI3 tMtHA3tNI.T SPILLWAY
E t'o-&101-
ALA V epw la
Al
F L71, t-
p ^ tf
Dimension PI should be 5' minimum.
Check the capacity of the emergency spillway.
Tables provided in Chapter 11 of the NRCS' Engineering Field Manual are recommended for
determining emergency spillway capacity.
2. An acceptable alternative is the use of the weir equation:
Q = CLH'-5
Where this option is used, the maximum value of C should be 2.8. L is the bottom width of the
spillway at the crest, and H is the depth of flow above the spillway crest. Note: Manning's
channel equation should not be used to size the spillway crest. However, it should be used to
design the outlet channel below the spillway crest.
3. The total of the emergency and principal spillway capacities must equal or exceed the required 2
cfs /acre discharge capacity.
363- 2134 -008 / April 15, 2000 / Page 55
WEIR
LINING
CHANNEL
DISSIPATER
BASIN
NO.
Z3
FT
Z4
F
TOP
ELEV
WTE
F
CREST
ELEV
WCE
F
WIDTH
Ww
FT
RIPRAP
SIZE
R-
RIPRAP
THICK.
LRt
IN
Z5
F
DEPTH
Cd
FT
LENGTH
DI
FT
WIDTH
Dw
FT
RIPRAP
SIZE
R-
RIPRAP
THICK.
DRt
IN
Dimension PI should be 5' minimum.
Check the capacity of the emergency spillway.
Tables provided in Chapter 11 of the NRCS' Engineering Field Manual are recommended for
determining emergency spillway capacity.
2. An acceptable alternative is the use of the weir equation:
Q = CLH'-5
Where this option is used, the maximum value of C should be 2.8. L is the bottom width of the
spillway at the crest, and H is the depth of flow above the spillway crest. Note: Manning's
channel equation should not be used to size the spillway crest. However, it should be used to
design the outlet channel below the spillway crest.
3. The total of the emergency and principal spillway capacities must equal or exceed the required 2
cfs /acre discharge capacity.
363- 2134 -008 / April 15, 2000 / Page 55