HomeMy WebLinkAboutStudies APPLICANT 12/13/2020B E JOHNSON
BRODERICK
ENGINEERING
Memorandum
Clayton McEachern, City of
To. Springfield
From: Mikael Shields, P.E.
Subject _ Stormwater System Design
325 West 13' Avenue
Eugene, Oregon 97481
541-338-9488 (office)
.JBEus.com
Date: November 5, 2020
Project Name: North Lake Storage Facility
JBE Project Number 20031.03
This memo describes the design intent of the stormwater system for the referenced project for
Zachary Reeves located at 4155 E Street, Springfield. The total site area is approximately 22,650
SY of which 13,892 S.F., or 61% is impervious surface (buildings and pavement) which includes
the Phase 1 and Phase 2 buildings. The remaining 8759 S.F. of the site is composed of
landscaped areas including the stormwater treatmentjnfiltration area. There is no public piped
stormwater system available adjacent to the property, therefore all runoff from the site will be
treated and infiltrated on-site in a stormwater planter facility designed in accordance with the
City of Eugene Stormwater Design Manual (ESDM). The adjacent paved parking and driveway
areas are graded to sheet drain directly to the stormwater planter while the building roof drains
will be piped and outfall along the perimeter as shown on the Site Plan Sheet C2.1. The
stormwater planter surface area is 1232 S.F. and has an allowable ponding depth of 12 inches.
The facility was sized using the stormwater Surface Filtration/Infiltration Facility Sizing
Spreadsheet found in the ESDM which is attached for reference. Infiltration testing performed
on the site revealed a high infiltration rate of 44 inches per hour, however in accordance with
the facility sizing spreadsheet instructions a conservative value of 2.5 inches per hour was used
to size the facility. During the flow control storm event the facility reaches a maximum ponding
depth of 10.8 inches which is contained within the footprint of the infiltration area.
m -mi Nnvamhor[ 9mn
Stormwater Surface Filtration9nfiltration Facility Sizing Spreadsheet
24 Hour Storm, NRCS Type 1A Rainfall Distribution
City of Eugene
North Lake P.M. Storage Facility Date: a1T,
4155 E Street Permit Number.';NFA,
Springfield OR Catchword ID: Site
MDS
Johnson Broderick Engineers
Complete this fame for each drainage catchment in the project site Thal is to be sized per the Presumptive Approach.
Provide s distinctive Catchment ID for each facility cowdim itcd with the site basin map to comelate the appropriate
calculations with the facility.
The maximum drainage ca chmew to he modeled per the Presumptive Approach is 1 acre (43,580 SF)
For infilimticn facilities in Class A or 6 soils whore no infiltration testing has been perFmmed use an infiltration rate of 0.5'nihr.
For all feelibes use a maximum soil mliliration note of 2.5 in/hr for topsoil/growing medium_
loose "Yes" from ghe dmpdown boxes below next to the design standards sequimmente, for this facility.
Pollution Reduction (PR) Yes
Flow Control (FC) No
Destination (DT) r_Y-;IAI lMltrobn faulty must se chosen as the ra,eny Ewe to meet m:r apn Mqueereents
Total Square Footage Impeorious Area- 13892 scift
Impervious Area CN -1 98
Total Square Footage of
Pre -Development
Total Square Footage Pervious Area= 8759 salt
Pervious Area cN=J 85
Time of Concentration Post Developmon O- min
Time
Tested Soil Infiltration Rate=®inlhr(am Note 4) Destination Design=inMr
Design Soil Infiltration Rate= 2 5 Whir Soil Infiltration Rate
[Raqui.nt
Rainfall Depth
Desi n Storm
Pollution Raductinn
14 inches
Water Quar
Flow Con[rol
36 inches
Flootl Control
Destination
1 3 6 inches
IFIcind Control
Surface Widl
Surface Lengl
Facility Side Slope
Max. Ponding Depth
in Storm eater Facility=
Depth of Growing Medium (Sol
101612020-9'.33 AM
Facility Surface
Facility Bottom P
Basin
Ratio of Facility Area
Peak Flow Rate to Stounwater Facility= 0.10Y ets
Peak Facility Overflow Rate-F-0 000 cfs
Total Runoff Volume [o S[onnwater�
=Of
Faulity 1464 cf
Total Overflew Volume=cf
Max. Depth of starmwater, in Facility- 03 in
Drawdown Timms 0 2 hours
Yes Facility Sizing Meets Pollution Reduction Standards?
YES Meets Requlmment of No Facility Flooding?
VES Meets Requiramentfor Maximum of 18 Hour Drawdown Time?
Flow Contml alculation Results
Peak Flow Rate m Stormwamr, Facility= 0.423 cls
Peak Facility Overflow Rate- 0.000 cfs
Total Runoff Volume to slormwate
Facility= 5327 ff
Total Overflew Velums= 0 of
Peak OR fte Flow Ra
Max. Depth of Stormwaterin Facility= 70.8 in
Filtration Facility Undardrafn= NV,cfs
Drawtlawn Tim¢- 0.8 hours
Pre-Developmeyd Runoff Data
Peak Flow Rate - 0.271 cls
Total R ... ffV.1u..=l 3971 cf
NW Facility Sizing Meets Flow Control Standards?
NV. Meets Requimmentfor Post D¢velnpment offsite Flow less or equal to Pre-Development Flow?
NV. Meets Requirement for Maximum of 18 Hour Drawdown Time?
estmahon- alcula0on Results
Peak Flow Rabe to Stormwater Facility = 0.423 cfe
Peak Facility Overflow Rale- 0.000 cis
Total Runoff Volume to Stormwater
Fadlity=Acf
Total Overflow Voluma= 0 ct
Max. Depth of Stormwater In Facility=in
Dmwtlown Time=hours
Yes Facility Sizing Meets Destination Standards?
YES Meets Requimmmd of Ne Facility Flooding?
VES ifileets, Requirement for Maximum of30 hour Dsmadawn Time?
101612020-933 AM