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HomeMy WebLinkAbout02944 - Technical Information Report - Drainage SURFACE WATER DRAIt�AGE
REPORT AND ANALYSIS
FOR - ,
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JIM'S AUTOMOTIVE Z� `��
Renton, Washington
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JUL 0 9 2001
BUILDING DI'JlSION
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S�ONAL�
EXPIRES 3�'2� OI �
Job No.: 01-019
SEGA Engineers�
Struct ral & Civil Consulting Engineers
22928 SE 312m ST (360)886-1017
Black Diamond,WA 98010
Copyright 2001,SEGA Engineers
21�l��
SUMMARY OF DRAINAGE ANALYSIS
FOR
� JIM'S AUTOMOTIVE
SECTION 19, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M.
RENTON, WASHINGTON
May 31, 2001
Introduction
This portion of the analysis is included to give a brief overview of the project and a
description of the existing storm drainage system on and off the site. For this analysis
one site visit was made to note the condition of the existing drainage system. Field
observations were completed on May 31, 2001.
The proposed project involves the construction of a new retail building, revised parking
facilities, and roadside improvements.
Existing site topographic maps, U.S.G.S. maps, City of Renton Storm Drainage maps,
and a field investigation were used to determine the existing drainage configuration.
Proposed Site
The project is located on the south side of Southwest 12�' Street midway between
Seneca Avenue SW and Lind Avenue SW, in Renton, Washington (see attached
vicinity map). The site is approximately 0.33 acres and is currently developed with
existing asphalt parking used for automobile storage. A new retail building with a floor
area of about 1,750 square feet will be located at the east central portion of the site
adjacent to the existing parking area. The existing residence on the east side of the
site has been previously demolished and removed. Approximately 700 sf of asphalt
parking will be removed for the new building and modified entrance and about 690 sf of
paved parking will be constructed on the north and south side of the new building.
Existing Drainage Conditions
Surface runoff from the existing paved area is conveyed to a storm drain system
beginning on the west side of the parking area. Surface runoff from the parking lot is
� �
Jirri s Automotive.
Drainage Analysis.
collected in a catch basin and conveyed via 8" ADS pipe to a catch basin on the south
side of SW 12th Street. Flows are then conveyed to the north side of SW 12�' Street
and west to Seneca Avenue SW. Conveyance continues in the public system west to
Raymond Avenue SW and then north to SW Grady Way.
Method of Analysis
Drainage calculations were performed using methods described in Chapter 3 --
Hydrologic Analysis, of the King County SurFace Water Drainage Manual. Peak runoff
rates for the pre-developed and post developed conditions were calculated using the
Santa Barbara Urban Hydrograph Method. The Water Works design program by
Engenious Systems was used to develop peak runoff rates for the various hydrographs.
DRAINAGE DESIGN CRITERIA
The calculations for analyzing the surface water discharge are based on the following
criteria:
Design Storm Rainfall: 2 yr, 24 hour = 2.00 in.
10 yr, 24 hour = 2.90 in.
100 yr, 24 hour = 3.90 in
Existing Conditions: Pervious area = 0.197 Acres
Impervious area = 0.137 Acres
SCS Curve Number: Pervious C�: 81
(Existing Conditions) If11pe1vlOUS C�: 98
Proposed Conditions: Pervious area = 0.193 Acres
Impervious area = 0.142 Acres
SCS Curve Number: Pervious C�: 90
(Developed Conditions) Impetvious C�: 98
Soil Type: Puget Silty Clay Loam (Pu)
SCS Group D .
.;
2
• , Juri s Automotive.
Drainage Analysis.
King County Drainage Manual -- Core Requirements
Core Requirement# 1. Discharge at the Natural Location:
The proposed development will in no way divert nor change the natural drainage
flow of the property and the discharge of all site drainage will continue to be at its
natural location. Downstream drainage continues as sheet flow across the site
to the north and enters the public conveyance system.
Core Requirement#2. Off Site Analysis:
A Level 1 analysis was conducted. We visited the site and found no signs of
erosion or other drainage problems at or around the proposed areas of
construction. There was no evidence of past flooding or slides. The Level 1
analysis indicated that the downstream conveyance system appeared adequate
and no drainage problems are predicted after development.
Core Requirement#3. Runoff Control:
The proposed project site post-developed peak runoff rate for the 100-year, 24-
hour duration design storm event is calculated to be less than 0.5 cfs more than
the pre-developed peak runoff rate for the site. This is conside�ed to be a
negligible peak runoff rate increase. Therefore, on-site peak rate runoff control
will not be required for the proposed project.
Core Requirement#4. Conveyance System:
The existing on-site conveyance system which consist of a parking lot catch basin
and underground storm sewer will carry flows to the public conveyance system. A
roof collection system will be added and connected to the existing catch basin.
Core Requirement#5. Erosion £�Sedimentation Contrvl Plan:
Standard erosion/sedimentation control measures should be adequate since the
area to be developed is relatively small and has minimal slope. We recommend
catch basin filters at two locations and these are shown on the design drawings.
We have also provided information on mulching and erosion control seeding and
plantings. We also recommend mulching disturbed areas which are to be left
uncovered for more that 24 hours during the months September through May.
Core Requirement#6. Maintenance and Operation:
A maintenance and operation requirement for private facilities will be provided
per the King County SWM.
Core Requirement#7. Bonds and Liability:
Bonding will be provided per the King County SWM.
3
_ ,.�n � :
� jim's Automotive.
Drainage Analysis.
�
Summary
Our Level I investigation indicates that there is no record of any drainage problem
within 1/4 mile downstream of the site nor are any drainage problems predicted after
development. The proposed development will not divert runoff from the natural existing
location. The increased rate of surface water discharge is negligible and no on-site
detention system is required. The proposed expansion is in compliance with the City of
Renton drainage codes and the King County Surface Water Design Manual.
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SEGA Engineers Project Jim's Automotive
Structural&Civil Consulting Engineers
Job No. 01-019 By: GAT
22928 SE 312th ST (360)886-1017
Black Diamond,WA 98010 Checked Date: 05/31/01 Sht �
Drainage Analysis Summary
Topic Pre-Developed Post-Developed
Land Use Landscape, Brush, Parking Grass, Building, Drives/Parking
A pervious (Acres) 0.197 0.193
C„ pervi0us 81 90
A impervious (Acres) 0.137 0.142
C„impervious gg gg
T� (min.) 29.65 �6
Precipitation (in.)
(24 hour)
2 yr. 2.00 2.00
10 yr. 2.90 2.90
100 yr. 3.90 3.90
Peak Q (cfs) Q Q (cfs)
2 yr. 0.08 0.12 0.04
10 yr. 0.13 0.19 0.06
100 yr. 0.20 0.27 0.07
COPYRIGHT 2001,SEGA ENGINEERS
6/1/Ol 8 :44 :20 am SEGA Engineers page �
JIM' S AUTOMOTIVE
EXISTING CONDTIONS
BASIN SUMMARY
BASIN ID: A10 NAME : 10 YR PRE DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs
RAINFALL TYPE. . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 .20 Acres 0 . 14 Acre�
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00
TC. . . . . 29 . 65 min 5 . 00 min
ABSTRACTION COEFF: 0 . 20
TcReach - Sheet L: 110 . 00 ns : 0 . 2400 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE: 0 . 13 cfs VOL: 0 . 05 Ac-ft TIME : 480 min
BASIN ID: A100 NAME: 100 YR PRE DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs
RAINFALL TYPE . . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 .20 Acres 0 . 14 Acres
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00
TC. . . . : 29 . 65 min 5 . 00 min
ABSTRACTION COEFF: 0 .20
TcReach - Sheet L: 110 . 00 ns : 0 .2400 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE: 0 .20 cfs VOL: 0 . 08 Ac-ft TIME : 480 min
BASIN ID: A2 NAME: 2 YR PRE DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs
RAINFALL TYPE. . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 .20 Acres 0 . 14 Acres
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00
TC. . . . . 29 . 65 min 5 . 00 min
ABSTRACTION COEFF: 0 .20
TcReach - Sheet L: 110 . 00 ns : 0 .2400 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE : 0 . 08 cfs VOL: 0 . 03 Ac-ft TIME: 470 min
6/1/O1 8 :45 : 1 am SEGA Engineers page ,�
JIM' S AUTOMOTIVE
PROPOSED CONDTIONS
BASIN SUMMARY
BASIN ID: B10 NAME: 10 YR POST DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs �
RAINFALL TYPE. . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 . 19 Acres 0 . 14 Acres
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00
TC. . . . . 18 . 86 min 2 . 33 min
ABSTRACTION COEFF: 0 .20
TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070
impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE : 0 . 19 cfs VOL: 0 . 06 Ac-ft TIME: 470 min
BASIN ID: B100 NAME: 100 YR POST DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs
RAINFALL TYPE. . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 19 Acres 0 . 14 Acres I
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00
TC. . . . . 18 . 86 min 2 . 33 min
ABSTRACTION COEFF: 0 .20
TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070
impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE: 0 .27 cfs VOL: 0 . 09 Ac-ft TIME: 470 min I
BASIN ID: B2 NAME: 2 YR POST DEV
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs
RAINFALL TYPE. . . . : KC24HR PERV IMP
PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 . 19 Acres 0 . 14 Acres
TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00
TC. . . . : 18 . 86 min 2 . 33 min
ABSTRACTION COEFF: 0 .20
TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070
impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070
PEAK RATE: 0 . 12 cfs VOL: 0 . 04 Ac-ft TIME: 470 min
6/1/O1 8 :45 : 58 am SEGA Engineers page �..
JIM' S AUTOMOTIVE
HYDROGR.APH SUMMARY
PEAK TIME VOLUME
HYD RUNOFF OF OF Contrib
NLJM R.ATE PEAK HYDRO Area
cfs min. cf\AcFt Acres
---------------------------------------------
---------------------------------------------
1 0 . 079 470 1315 cf 0 . 33
2 0 . 132 480 2212 cf 0 . 33
3 0 . 197 480 3280 cf 0 . 33
4 0 . 117 470 1677 cf 0 . 33
5 0 . 187 470 2695 cf 0 . 33
6 0 . 266 470 3858 cf 0 . 33
11 0 . 020 900 1878 cf 0 . 33
12 0 . 099 530 4085 cf 0 . 33
13 0 . 099 530 4086 cf 0 . 33