HomeMy WebLinkAboutDick Lanyons Memo on the Storwmwater Management Master Plan SMMP UpdateTo: Stephen McComb, Evanston Utilities Commission Chair
From: Dick Lanyon
Subject: Stormwater Management Master Plan (SMMP) Update
November 18, 2024
On October 18, 2024, Bridget Nash, PE, Senior Project Manager in the Bureau of Capital
Planning and Engineering, Public Works Agency, City of Evanston, appeared before members of
the Evanston Utilities Commission and others, to present an update of the Evanston SMMP,
focusing on the recommendations on pages 5-1 through 5-12 of the final SMMP report. Ms.
Nash used slides during her presentation. The meeting was not an official commission meeting
because a quorum was not present. Nevertheless, the presentation was informative and is
summarized for the purpose of sharing with commission members who were not present and the
public.
The recommendations are in three categories, private system, regulations, and public system. The
private system pertains to methods for improving the level of protection against flooding of
private property.
• Overhead sewers are considered the most reliable way to eliminate basement flooding
due to sewer backup.
• Sewer backflow prevention valves close automatically when sewage flows toward rather
than away from the structure.
• Sump pumps and drain tiles collect groundwater and roof drainage, and move it away
from the structure.
• Grading the ground surrounding the structure to move surface drainage away from the
structure.
• Floodproofing includes sealing foundation walls and window wells, elevating basement
equipment, and securing below -grade entryways.
Structures that employ some or all of these methods have already improved the level of
protection against flooding. For structures that lack these methods, the challenge is to provide
incentives for the property owner to install needed methods or to legislatively require their
installation.
Regulations provide standards for stormwater management on private property. Existing
stormwater regulations include the Metropolitan Water Reclamation District's Watershed
Management Ordinance which imposes runoff and volume controls for parcels greater than 0.5
acres and detention on parcels greater than 3 acres. Evanston has several existing regulations for
stormwater management and drainage.
Building regulations require stormwater detention with certain exceptions for all new
developments.
0 The plumbing code limits the disposition of roof and subsoil drainage.
• The property maintenance code limits the disposition of downspout and foundation
drainage.
• Compliance with floodplain regulations is required where applicable.
• The green building ordinance applies to new construction greater than 10,000 square feet,
interior renovations greater than 5, 000 square feet, and area -based best management
practices.
Evanston's regulations can be strengthened to improve the level of protection against flooding.
• Detention requirements can be extended to cover all properties.
• The plumbing and property maintenance codes can apply to all properties at all times,
not just when changes are made, and specify stormwater control methods.
• Alternatively, compliance with these codes can be required when property ownership
transfers.
Legal authority may need to be determined for strengthening these regulations. The challenge in
strengthening Evanston's codes and requirements is to allow variations where compliance poses
an excessive burden on property owners, or to find financial incentives to ease the burden of
compliance. It is anticipated that code and regulation changes may be included in the Evanston
Envision 2045 planning program.
The public system offers opportunities in improve stormwater management in future capital
improvement projects and to continue to improve the calibration and verification of Evanston's
stormwater management hydrologic and hydraulic model. Three conceptual capital improvement
projects were included in the SMMP report.
The Combined Sewer Basin 07 project is within the 21 and 51 Wards, roughly bounded by the
North Shore Channel, Green Bay Road, Asbury Avenue, Dempster Street, Dodge Avenue and
Church Street. The area is low and likely will have surface flooding during a 100-year storm
frequency. Also, the area is mostly served by combined sewers and homeowners have reported
sewage backup in basements. The area is drained by a 100-year-old sewer under Emerson Street
and outfall to the North Shore Channel, both owned by the MWRD. Due to climate change the
10-year storm frequency level of protection under the 1990 Relief Sewer Program is now a 2-
year storm frequency level of protection.
To relieve surface flooding, basement sewer backup and provide a 10-year storm frequency level
of protection, it is proposed to construct a new local sewer in Darrow Avenue draining from the
north and south, connecting to a new trunk sewer in Emerson Street draining to the west and
discharging into the North Shore Channel. The probable cost of this improvement is $6,400,000.
The Southwest Surface Flooding Improvement project is within the 81 and 91 Wards, roughly
bounded by Cleveland Street, Dewey Avenue, Kirk Street, Dodge Avenue, Oakton Street and
Hartrey Avenue. The area is low and likely will have surface flooding during a 100-year storm
frequency due to the lack of surface drainage pathways to the North Shore Channel. Although
surface drainage is handled by storm sewers, the sewer system can be surcharged by high water
in the channel. Like the previous project area, due to climate change the 10-year storm frequency
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level of protection under the 1990 Relief Sewer Program is now a 2-year storm frequency level
of protection.
To relieve surface flooding and provide a 10-year storm frequency level of protection, it is
proposed to construct local sewers in several east -west streets that connect to new north -south
trunk sewers in Dodge, Hartrey and Grey avenues, and the trunk sewers connect to a new larger
west -flowing sewer in Cleveland Street that discharges through a new outfall to the North Shore
Channel. The probable cost of this improvement is $16,100,000.
The Mason Park Green Infrastructure Improvement is being considered as part of the Mason
Park Expansion project in the 21 Ward. The area south of Mason Park along Davis Street, Grey
Avenue and the alley west of Grey (sometimes referred to as Darrow Avenue) is low and subject
to surface flooding due to the former railroad embankment to the west. Surface flooding
increases the risk of combined sewer surcharge.
To relieve surface flooding, a bioswale can be incorporated in the park expansion to detain
surface floodwater, allowing some infiltration in sandy subsoils. Excess stormwater in the
bioswale will be released slowly through a new sewer connecting to an existing relief sewer west
of the former railroad embankment. Curb stormwater inlets to the combined sewers in Davis
Street and Grey Avenue will be disconnected and redirected to the bioswale via new storm
sewers. The probable cost of this improvement is $900,000.
The engineering staff of the bureau are using the stormwater hydrologic and hydraulic model to
analyze and understand the drainage aspects of other projects in the capital improvement
program, including 4 alley improvement projects in 2024 totaling 2,400 lineal feet and the
proposed 2025 projects. The staff is also monitoring those areas identified in the SMMP with
surface flooding risk.
In spring and summer 2025, the sewer maintenance division, under the guidance of bureau
engineers, will be installing water level meters to further calibrate and verify model performance.
The model will be updated if needed.
Copy to Bridget Nash
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