FLOOD03450

• County: Jefferson
• Community: Lakewood
• Basin: South Platte
• Title: Storm Drainage Criteria City of Lakewood
• Date: 8/9/1982
• Prepared For: Lakewood
• Floodplain - Doc Type: Educational/Technical/Reference Information

Page 46

Let's use a notch to control QlOO

QNotch = QlOO - QOrifice
QOrifice = ,6 x tr
= 0.85

2
x .38 x
4

1
(2 x 32,2 x 2,6) ~

QNotch = 3,50 - 0.85 = 2.65 cfs

A V-notch provides a theoretically neat solution where the depth of the notch,
D = HlOO - H5' but this writer prefers a contracted weir as follows:

To assure proper proportioning: Let B = 3H

Substituting in the Francis Eqn.

Where:

Q = discharge
B = width of wier
N = no. of contractions
H = depth

Where:

Q = 3.33 (B - . loR) H3/2
= 3,33 (3H - ,2H) H3/2
= 3.33 (2,8H) H3/2
= 9.32 H5/2
H =L Q \2/5 = (2,65)2/5 =
~2/ 9.32

.60'

= 7\"

Thus:

B = 3H = 1.80' = l' - 9~"

Check emergency overflow from excess stormwater passage:
for this problem let T = 15 minutes
c
then QlOO = ,7 x 5,9 x 3.5 = 14.4 cfs

from Fig 2, I = 5,9 in/hr,

thru l2"~ outlet pipe with H/D = 3,6, Q = 8.0 cfs which is less than QlOO
= 14,4 cfs thus any other excess stormwater passage overtops the berm

Normally, it would be preferred to have excess storm water passage overtop the
detention basin and revert to sheet flow, For this case, when there is a
level berm, the berm becomes a broad crested weir, Check the depth and velo-
city of flow and assess any likely undesirable effects of this type of flow,

Where it is desirable to concentrate the excess storm water passage into a
channel, swale, gutter or ditch, or when the velocity of flow overtopping the
berm is great, then sufficient protection shall be provided to prevent damage
to the detention pond,