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40 � �
RY JACp
OUR JOB NO. 5616 � pgweS
AUGUST 8, 1996 h
769
EXPIRES lO/10/
Prepared By:
BARGHAUSEN CONSULTING ENGINEERS, INC.
1 821 5 72ND AVENUE SOUTH I AUG 1 ;1 1996
KENT, WASHINGTON 98032
isI �Q`GHAU (206) 251 -6222
m %
�a e CIVIL ENGINEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES
�'"HQ.00
• 1.0 INTRODUCTION AND GENERAL INFORMATION
The proposed project site consists of approximately 0.6 acres of previously developed land. As
required by King County Surface Water Design Manual 1990, on-site peak rate run-off control will
not be required for the proposed project in the following situations:
For negligible peak run-off rate increase:
1.1 The proposed project site post-developed peak run-off rate for the 100-year/24-hour
duration design storm event is calculated to be less than 0.5 CFS more than the peak run-
off rate for the existing site conditions and/or the project proposes to construct 5,000
square feet or less of new impervious surface.
The calculations following herewith show that we meet both those conditions. When you review
the calculations contained herewith, you will notice that the 100-year/24-hour proposed site
conditions peak run-off rate was 0.46 CFS, whereas the 100-year/24-hour existing site conditions
peak run-off rate was 0.42 CFS. Therefore, the difference is less than the 0.5 CFS increase
allowed. Therefore, peak rate run-off control is not required for this project.
•
•
5616.011 [JJ/jss]
8/8/96 9: 18 :25 am Barghausen Engineers page 1
ARCO REMODEL @ NE 30TH AND I-405
• BASIN DESIGN
BASIN SUMMARY
BASIN ID: 100DEV NAME: 100 YR/24 HR PROPOSED SITE
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0. 57 Acres BASEFLOWS: 0 . 00 cfs
RAINFALL TYPE. . . . : TYPElA PERV IMP
PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0. 08 Acres 0. 49 Acres
TIME INTERVAL. . . . : 10. 00 min CN. . . . : 86. 00 98 . 00
TC. . . . . 3 . 38 min 1. 77 min
ABSTRACTION COEFF: 0. 20
TcReach - Sheet L: 30. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 3300
impTcReach - Sheet L: 180. 00 ns: 0. 0110 p2yr: 2 . 00 s: 0. 0450
PEAK RATE: 0.46 cfs VOL: 0. 17 Ac-ft TIME: 470 min
BASIN ID: 100PRE NAME: 100 YR/24 HR EXISTING SITE
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0. 52 Acres BASEFLOWS: 0. 00 cfs .
RAINFALL TYPE. . . . : TYPEIA PERV IMP
PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0. 07 Acres 0. 45 Acres
TIME INTERVAL. . . . : 10. 00 min CN. . . . : 86 . 00 98 . 00
TC. . . . . 3 . 38 min 1. 19 min
ABSTRACTION COEFF: 0. 20
TcReach - Sheet L: 30. 00 ns: 0. 4000 p2yr: 2 . 00 s: 0. 3300
impTcReach - Sheet L: 110. 00 ns: 0. 0110 p2yr: 2 . 00 s: 0 . 0455
•
PEAK RATE: 0.42 cfs VOL: 0. 15 Ac-ft TIME: 470 min
0
8/8/96 9: 18 : 25 am Barghausen Engineers page 2
ARCO REMODEL @ NE 30TH AND I-405
. BASIN DESIGN
HYDROGRAPH SUMMARY
PEAK TIME VOLUME
HYD RUNOFF OF OF Contrib
NUM RATE PEAK HYDRO Area
cfs min. cf\AcFt Acres
---------------------------------------------
---------------------------------------------
1 0. 420 470 6611 cf 0. 52 `0Q
2 0. 462 470 7233 cf 0 . 57 /00 yr?- Dg5vF_L�pP��
•
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