HomeMy WebLinkAboutCOM 0306.002 2006-2008 ENGINEERING
July 21, 1995
County of Hawaii
Public Works Engineering
Kona Office
Attention: Mr. Tom Pack
Subject: Keanahalululu Subdivision Drainage Calculations
TMK: (3) 5-9-07: 07; Folder No. 5941
Mr. Pack,
The following calculations address the above project drainage in
the before and after development conditions. The Rational Method
was used in determining the anticipated flows. Based upon the
following calculations, it is our opinion that the 6 proposed dry
wells located within the road right of way are adequate to handle
the anticipated increase in flow.
o Present Condition
Area: 28.83 ac Length: 550 if Slope: 8g Ave Tm (10 yr) 1.5
C: Infiltration 0.07 Tc: 15 min
Relief 0.06 I: 2.7
Cover 0.05
Develop. Type 0.15
0.33
Q = CIA = (0.33)(2.7)(28.83) = 25.7 cfs
o After Development Condition: Additional Flow I
Due to Paved Area's
Paved Area: Roadway's: 1.14 ac Driveway's & House's: 0.6 ac
Length: 600 if Slope: 8°s Ave Tm (10 yr) 1.5 I,
C: 0.95 (Paved Area) Tc: 6 min '
I: 3.7
Roadway: Q = CIA = (0.95)(3.7)(1.14) = 4.0 cfs
~ House & Driveway's: Q = (0.95)(3.7)(0.6) = 2.1 cfs
Remaining Undeveloped Area:
Q = CIA = (0.33)(2.7)(27.09) = 24.2 cfs
Total Q = 4.0 + 2.1 + 24.2 = 30.3 cfs
Comm. No.
Additional Flow: 30.3 cfs - 25.7 = 4.6 cfs Ref. To: r~
Ref. Date~)t)N 1 9 2007
'i Phone: (808) 329-7400 Fax: (808) 329-7202
74-5588 PAW AI PLACE, BLDG. I P.O. BOX 390548 •KAILUA-KONA, HAWAII 96739
In conclusion, the after development condition increases the runoff
by 4.6 cfs to be handled by the proposed 6, 8 ft deep dry wells.
Assuming that each 8 ft dry well is capable of handling 2 cfs, the
6 proposed dry wells are adequate to handle the anticipated flow
and increase due development.
Sincerely,
TRI I I
1
David A. Grenier, P.E.
S. ~r,
- ~~nVO
i
~ 1, I~j '
N~ , \ ,,1,
,
~~~f ~ , ~ ~
i.~s•:~~' iii'
~ •r.
I ~ ~ , I
b
II i~ II I 1 N
A ,~\1 \ I11~I /~~7 m
~ ~ l' ~ ` ~ ~
Jai/AI
\\~~1
•
;l
. --.~`tiJ ~ ~
• \ ~ IN~
~ . \ <<
r.a-. ~
i x
g o.
i ~
v
b