HomeMy WebLinkAboutCorrespondence APPLICANT 6/16/2008
Page I of I ,
HOPKINS Steve.
From: Jennifer Holcomb [JenniferHolcomb@kpffcivilpdx.com]
Sent: Monday, June 16, 20084:00 PM
To: HOPKINS Steve
Cc: Matt Keenan
Subject: Fire Station #16 Pre- vs. Post-Storm Drainage
"
Date Received:
Planner: SH
&/ilnlo"X'
I I.
Steve-
The following is the comparison between pre- and post-development of the fire station site as it relates to storm runoff:
I
I Pre
I Post
. Impervious Area (Acre)
0.59
0.66
. Pervious Area (Acre)
0.41
0.34
With respect to flows, I ran the analysis for the 25-year storm to determine flow values (0) in cubic feet per second (cfs).
The existing site has two points of discharge, one for the trench drain at the driveway and one that collects the rest of the
site (per the survey) and discharges into the 12" storm line on Main Street. The proposed site plan has three discharge
points, one for the trench drain at the driveway (minimal change therefore disregarded for these calculations), and two for
the site (one discharges to the 12" line in Main St. and the other from the bioswale/filtration basin to the 18" storm line in
68th place). The following table presents the analysis for the pre- vs. post- flows for the two connection points.
I Pre
I Post
, 0 (cfs) to 12" in Main
St.
0.93
0.69
, 0 (cfs) to 18" in 68th PI. '0 (cfs) Total
0.93
0.29 0.98
The proposed site has a slight increase of impervious area (7%) and increased runoff of 5% from existing conditions. The
biggest difference between pre- and post is the number of discharge points. The line from 68th PI. does not junction with
the 12" line in Main Street. Depending on which line has capacity issues, this may help the situation.
If you have any questions about the above information, please let me know.
Thanks,
Jenn
Jennifer L. Holcomb, PE, PSP, BSCP
Project Engineer
KPFF Consulting Engineers
1201 Oak Street, Suite 100
Eugene, OR 97401
541-684-4902
541-684-4909 Fax
541-514-6373 Cell
6/1 6/2008