HomeMy WebLinkAboutApplication APPLICANT 5/12/2021 (2)Memorandum
To: Bo Cromelin April 23, 2021
Company: BRFI Gateway, LLC
From: Geoff Larsen
Subject: Shoppes at Gateway Tentative Subdivision Plat
Stormwater Systems Overview
Summary:
This memo provides a broad -level summary of the existing stormwater systems within the Shoppes at
Gateway site to support the current Tentative Subdivision Plat for the site. The following provides an
overview of the existing public stormwater infrastructure, existing private stormwater infrastructure, and
existing stormwater management systems on the site.
Public Stormwater Infrastructure:
There are several public stormwater mainlines extending within easements through the site. These
mainlines convey stormwater runoff from public roadways and are summarized as follows:
• Northern System: A public mainline (24" and 42") extends along the northly edge of the site in
an east -to -west direction, discharging to the public open channel along the western edge of the
site. This system conveys drainage from Gateway Street and Gateway Loop.
• Southwestern System: A public mainline (42"48") enters the eastern edge of the site near the
LTD bus station and extends south and west, following the ring road, to discharge to the
southern end of the public open channel at the west side of the site. This system coveys
drainage from Gateway Street and the residential neighborhood to the east of the site,
surrounding Oakdale Avenue.
• Southern System: A public mainline (42") enters the site at the intersection of Harlow Road
and Beverly Street and extends through the site in a westerly direction (south of Walmart) to
discharge to the 60" mainline at the south west corner of the site. This system conveys
drainage from Harlow Road and Beverly Street.
• Western System: There is a public open drainage channel extending along the western edge
of the site, flowing north -to -south. The Northern, Southwestern, and Southern systems noted
above outfall to this channel. The public open drainage channel is designated as a wetland.
The channel transitions to a 60" pipe near the southern end of the site and continues to the
south under Harlow Road.
Private Stormwater Infrastructure
Stormwater runoff from the majority of existing development site is collected through a closed -pipe
system, draining to the public open channel located along the west perimeter of the site (Western
System, as noted above). There are (3) 24" outfalls to the public open channel conveying runoff from
the western side of the site and there are (2) 48" outfalls conveying runoff from the eastem, southern,
and northern sides of the site. In addition to the closed -pipe drainage system, a large area of existing
parking lot along the western edge of the site sheet drains to the west edge of the parking lot and
discharges to the public open channel through a series of curb openings and rock lined channels.
Stormwater Management
w rnazzetti.com
T 541.686.8478
MAZZErn BHEGroup 940 Willamette Street, Suite 310, Eugene, OR 97401
Stormwater management improvements have been made to the site over the course of redevelopment.
At present it is estimated that roughly 20%-30% of the site receives vegetated stormwater treatment.
The following is a summary of the key improvements that have been made to the site:
• Double Chamber Catch Basins and Filter Insertsd
Many of the catch basins throughout the site have been retrofitted with double chambered
catch basins and/or filter inserts.
• Buffalo WIId Wings Swale
Runoff from the northern part of the Buffalo Wlld Wings parking lot is managed by an infiltration
rain garden located between the parking lot and the entrance drive to the north.
• Walmart Parking Lot Rain Gardens / Swales:
Runoff from the majority of the Walmart parking lot is managed with one of two rain gardens
within the parking lot.
• Eastern Parking Lot Rain Gardens:
In 2015, a large part of the eastern parking lot was redeveloped. Runoff from the majority of
this redeveloped parking lot is managed in a series of infiltration rain gardens integrated with
the parking lot landscaping.
• Western Outfall Improvements:
As part of the 2015 redevelopment project, the outfalls at the western edge of the site
improved to. The improvements consisted of creating shallow vegetated forebays to enhance
sedimentation and improve water quality. These enhancements were not designed improve
sedimentation but were not designed to provide treatment of the upstream contributing area.
G:Eugene\Projects\20M2 067-Shoppes at Gateway ADA and Parking StudyWDistlplines\CMRdELETE\T.Wive SubdMsi. Rah
Stmmwater Management Memo.dou 12
eHMmp Engin-nng Sur-Nng I Cmvlmg