HomeMy WebLinkAbout2020-07-21 City Council Work Session Meeting PacketAgenda
City Council Work Session
City of Edina, Minnesota
VIRTUAL MEETING
Call 833-360-0793, enter Conference ID 1065005 to listen to meeting
Tuesday, July 21, 2020
5:30 PM
I.Call To Order
II.Roll Call
III.Local Speed Limit Evaluation
IV.MOTION TO CLOSE SESSION: As permitted by Minn. Stat. 13D.05
Subd. 3(b) for Attorney-Client Privilege to Discuss Robert C. Tengdin,
Trustee of the Robert C. Tengdin Revocable Trust dated May 18,
2009 v. City of Edina
V.Update on Robert C. Tengdin, Trustee of the Robert C. Tengdin
Revocable Trust dated May 18, 2009 v. City of Edina
VI.Motion to move back into Open Session
VII.Adjournment
The City of Edina wants all residents to be comfortable being part of the
public process. If you need assistance in the way of hearing ampli5cation, an
interpreter, large-print documents or something else, please call 952-927-8861
72 hours in advance of the meeting.
Date: July 21, 2020 Agenda Item #: III.
To:Mayor and City Council Item Type:
Reports / Recommendation
From:Andrew Scipioni, Transportation Planner
Item Activity:
Subject:Local Speed Limit Evaluation Action, Discussion
CITY OF EDINA
4801 West 50th Street
Edina, MN 55424
www.edinamn.gov
ACTION REQUESTED:
Review and comment on staff's draft recommendation for reducing local speed limits, and provide further
direction.
INTRODUCTION:
See attached staff report.
ATTACHMENTS:
Description
Draft Staff Report to the Transportation Commission: Local Speed Limit Evaluation, July 10, 2020
July 10, 2020
Transportation Commission
Andrew Scipioni, Transportation Planner
Local Speed Limit Evaluation [DRAFT]
Executive Summary
This report is a summary of the analysis conducted to direct the City of Edina’s approach to setting speed
limits on local streets in accordance with City policies and recent State legislation. The current speed limit
on most streets owned by the City of Edina is 30 miles per hour (mph), which is the statutory urban speed
limit set by the Minnesota State Legislature. Effective August 1, 2019, cities have the authority to set speed
limits on streets they control.
The recommended speed limits on local streets are as follows:
30 mph on four-lane major streets
25 mph on two-lane major streets
20 mph on major streets within School Zones (no change from current restriction)
20 mph on minor streets
15 mph on minor streets within School Zones (no change from current restriction)
10 mph on alleys (no change from current restriction)
Speed limits on streets owned by other jurisdictions will remain as they are, unless changed by their
respective agencies. These include streets owned by the Minnesota Department of Transportation,
Hennepin County and private streets.
These new speed limits are recommended based on the findings from detailed technical analysis, including:
Lower speeds reduce the likelihood and severity of motor vehicle crashes.
Utilizing the 85th-percentile to set speed limits prioritizes motor vehicle traffic over the safety of all
modes of transportation, including pedestrians and cyclists.
REPORT / RECOMMENDATION Page 2
Lower speed limits promote public health and safety and support the goals established in the
Comprehensive Plan and the Living Streets Plan.
A tiered approach to local speed limits is most appropriate for Edina given the wide range of traffic
volumes and percentage of non-local traffic on city streets. This approach is consistent with that
implemented by other cities that strive to accommodate all modes of transportation.
Background
In 2006, Edina’s Transportation Commission recommended that City Council adopt a resolution
recommending a 25-mph speed limit policy in residential areas. City staff, at the time, instead recommended
that Council adopt a resolution supporting lowering the statutory urban residential speed limit from 30 to
25 mph. Council subsequently passed Resolution 2006-64, which stated that “the City of Edina does hereby
strongly support a statewide lowering of the speed limit from 30 miles per hour to 25 miles per hour on
local, residential roadways.” Rationale provided in the resolution included:
“Drivers traveling at high speeds are less aware of their surroundings and have less time to notice
and react to pedestrians and bicyclists.”
“Relatively small increases in vehicle speed can greatly increase the chances that a pedestrian will die
in a vehicle-to-pedestrian crash.”
“Experts on street design say that 20 to 25 miles per hour is the maximum safe speed for residential
streets.”
“The City of Edina supports ensuring speed limits maximize safety for all roadway users including
drivers, pedestrians and bicyclists.”
In 2008, Council adopted Resolution 2008-27, requesting State Representative Ron Erhardt sponsor
legislation granting permission to form a Speed Limit Task Force to begin a state-wide study of the feasibility
of 25 mph speed limits and that said study be completed before the start of the 2009 legislative session. The
2008 Comprehensive Plan also included the following policy statements:
“Support state legislation to decrease statutory urban speed limits from 30 to 25 miles per hour.”
“Complete speed zone studies and establish speed zones for Safe Routes to School.”
In 2009, the City received Safe Routes to School (SRTS) funding for implementation of a city-wide school
speed zone study. This study was prepared by WSB & Associates, Inc. and evaluated conditions near six
elementary schools, two middle schools, one high school and three private schools in Edina. The purpose of
the study was to “determine and implement school speed zones adjacent to each school” and to “provide
safe conditions to encourage students to walk and bike to school.” Council subsequently adopted Resolution
2009-66, adopting the Edina Schools Speed Zone Study and authorizing implementation of the
recommended signage plan. New signage was installed prior to the start of the 2009/2010 school year.
In 2012, the Transportation Commission wrote an advisory communication to Council recommending that
the City revise its speed limit policy to be more consistent with current state legislation and “accurately
communicate the authority the City has to reduce speed limits.” The Commission noted that the City had
REPORT / RECOMMENDATION Page 3
previously lowered speed limits on some local streets with bike lanes to 25 miles per hour and had
established reduced speeds in school zones as permitted by state statute.
Between 2013 and 2015, the City developed and adopted the Living Streets Policy and Plan. Living Streets
balance the needs of motorists, bicyclists, pedestrians and transit riders in ways that promote safety and
convenience, enhance community identity, create economic vitality, improve environmental sustainability,
and provide meaningful opportunities for active living and better health. Living Streets principles that guide
the City’s approach to speed limits include:
“Living Streets are high-quality transportation facilities that meet the needs of the most vulnerable
users such as pedestrians, cyclists, children, seniors and the disabled.”
“Living Streets provide access and mobility for all transportation modes while enhancing safety and
convenience for all users.”
“Living Streets will improve the current and future quality of life of the public.”
These principles are further echoed in the draft 2018 Comprehensive Plan, which notes that today’s primary
transportation planning focus includes increasing safety and ensuring that the transportation needs of all
users will be considered and all modes will be appropriately accommodated.
Between 2011 and 2019, the City’s biennial Quality of Life survey asked residents to assess traffic concerns
in their neighborhoods. About 40% of residents have consistently expressed that speeding is a moderate-to-
extreme problem in their neighborhood.
In May 2019, the Minnesota Legislature passed and Governor Tim Walz signed legislation granting cities the
authority to set speed limits on streets they control:
“A city may establish speed limits for city streets under the city’s jurisdiction other than the limits
provided in subdivision 2 without conducting an engineering and traffic investigation. This subdivision
does not apply to town roads, county highways, or trunk highways in the city. A city that establishes
speed limits pursuant to this section must implement speed limit changes in a consistent and
understandable manner. The city must erect appropriate signs to display the speed limit. A city that
uses the authority under this subdivision must develop procedures to set speed limits based on the
city’s safety, engineering, and traffic analysis. At a minimum, the safety, engineering, and traffic
analysis must consider national urban speed limit guidance and studies, local traffic crashes, and
methods to effectively communicate the change to the public.”
- Minnesota Statues, Section 169.14, Subd. 5h
Existing Conditions
The current speed limit on most local streets in Edina is 30 mph, which is the statutory urban speed limit for
the State of Minnesota. The speed limit on Hennepin County roads in Edina varies between 30 and 40 mph.
The speed limit for Minnesota Department of Transportation (MnDOT) trunk highways in Edina is 55 mph.
Figure 1 shows all existing speed limits within Edina.
REPORT / RECOMMENDATION Page 4
Figure 1: Existing Speed Limits (as of January 2020)
REPORT / RECOMMENDATION Page 5
National Research and Guidance
National Transportation Safety Board
In 2017, the National Transportation Safety Board (NTSB) published “Reducing Speeding-Related Crashes
Involving Passenger Vehicles,” a safety study examining causes, trends and countermeasures to prevent these
types of crashes. The findings of this study include:
“Speed increases the likelihood of serious and fatal crash involvement, although the exact
relationship is complex due to many factors.”
“Speed increases the injury severity of a crash.”
The Manual on Uniform Traffic Control Devices (MUTCD) guidance for setting speed limits in
speed zones is based on the 85th percentile speed, but there is not strong evidence that, within a
given traffic flow, the 85th-percentile speed equates to the speed with the lowest crash involvement
rate on all road types.”
“Unintended consequences of the reliance on using the 85th-percentile speed for changing speed
limits in speed zones include higher operating speeds and new higher, 85th-percentile speeds in the
speed zones, and an increase in operating speeds outside the speed zones.”
“The safe system approach to setting speed limits in urban areas is an improvement over
conventional approaches because it considers the vulnerability of all road users.”
Among the recommendations of this report is for a revision to the MUTCD to “incorporate the safe system
approach for urban roads to strengthen protection for vulnerable road users.”
National Association of City Transportation Officials
The National Association of City Transportation Officials (NACTO) identifies two different approaches for
setting urban speed limits.
Citywide
Under this approach, a city designates a speed limit that applies to all roadways within their
jurisdiction. NACTO recommends a 25-mph speed limit for this strategy. “Setting or lowering
default citywide speed limits is an inexpensive, scalable way to quickly improve safety outcomes, and
establish a basis for larger safety gains. Default citywide limits also provide consistent expectations
and messages about speed across the jurisdiction, which is easy for drivers to follow.”
Category of Street
Under this approach, a city develops a tiered system of speed limits. NACTO recommends the
following tiered system:
25 mph on Major streets. “Major streets feature a combination of high motor vehicle traffic
volume, signalization of major intersection, and an inherently multimodal street
environment.”
REPORT / RECOMMENDATION Page 6
20 mph on Minor streets. “Minor streets include physically small streets where low speeds
are often already present, as well as low-vehicle-volume streets with few or no transit
stops.”
10 mph on alleys and shared streets
“Citywide speed limits are generally easier to implement and may be easier for driver to follow. However, in
cities where there is clear differentiation between major arterial streets and local or minor streets, setting
speed limits based on category of street can sometimes allow cities to lower speed limits on a large number
of streets below what would be allowable citywide (i.e. 20 mph on minor streets vs. 25 mph citywide). If
cities have the authority to set default speed limits, they should decide whether to implement citywide limits
or category limits based on what makes sense given the local conditions.”
Manual on Uniform Traffic Control Devices
The Manual on Uniform Traffic Control Devices (MUTCD), published by the Federal Highway
Administration (FHWA), defines the standards used to install and maintain traffic control devices on public
transportation systems. The current MUTCD includes the following standards and guidance related to speed
limits:
“Speed zones (other than statutory speed limits) shall only be established on the basis of an
engineering study that has been performed in accordance with traffic engineering practices. The
engineering study shall include an analysis of the current speed distribution of free-flowing vehicles.”
“The Speed Limit sign…shall display the limit established by law, ordinance, regulation or as adopted
by the authorized agency based on the engineering study. The speed limits displayed shall be in
multiples of 5 mph.”
“State and local agencies should conduct engineering studies to reevaluate non-statutory speed
limits on segments of their roadways that have undergone significant changes since the last review,
such as the addition or elimination of parking or driveways, changes in traffic control signal
coordination, or significant changes in traffic volumes.”
“When a speed limit within a speed zone is poster, it should be within 5 mph of the 85th percentile
speed of free-flowing traffic.”
“Other factors that may be considered when establishing or reevaluating speed limits are the
following:
A. Road characteristics, shoulder condition, grade, alignment, and sight distance;
B. The pace;
C. Roadside development and environment;
D. Parking practices and pedestrian activity; and
E. Reported crash experience for at least a 12-month period”
The National Committee on Uniform Traffic Control Devices (NCUTD) recently recommended changes to
the current MUTCD guidance related to speed limits to the FHWA. These recommendations included:
Removing the standard that “the engineering study shall include an analysis of the current speed
distribution of free-flowing vehicles.”
REPORT / RECOMMENDATION Page 7
Upgrading and revising the considerations for establishing speed zones to read “Factors that should
be considered when establishing or reevaluating speed limits within speed zones are the following:
A. Speed distribution of free-flowing vehicles (such as current 85th percentile, the pace, and
review of past speed studies)
B. Reported crash experience for at least a 12-month period relative to similar roadways
C. Road characteristics (such as lane widths, curb/shoulder condition, grade, alignment,
median type, and sight distance)
D. Road context (such as roadside development and environment including number of
driveways and land use, functional classification, parking practices, presence of
sidewalks/bicycle facilities)
E. Road users (such as pedestrian activity, bicycle activity).
Revising the guidance statement regarding the posted speed limit being made within 5 mph of the
85th percentile speed to apply only “on freeways, expressways, or rural highways.”
The FHWA will consider whether to incorporate these recommendations into the next edition of the
MUTCD. MnDOT utilizes a slightly different version referred to as the MN MUTCD. Both documents are
identical in language related to speed limits. If the MUTCD is updated, it is anticipated that the MN MUTCD
will be updated accordingly.
Safety Implications
Vehicle stopping distance is an important factor in the likelihood of a crash. Figure 2 shows the correlation
between vehicle speed and average stopping distance as calculated by the American Association of State
Highway and Transportation Officials (AASHTO). For example, a reduction from 30 to 20 mph results in an
additional 85 feet (or about 5 car lengths) of stopping distance.
Figure 2. Average Stopping Distance vs. Speed (AASHTO)
80
112
151
197
247
301
0 50 100 150 200 250 300 350
15
20
25
30
35
40
Average Stopping Distance, feetVehicle Speed, mph
REPORT / RECOMMENDATION Page 8
Exact stopping distance calculations vary depending on specific reaction times and braking speed, but when
controlling for those variables, higher speeds always result in longer stopping distances.
Speed also impacts the severity of injury resulting from crashes, particularly for pedestrians and cyclists.
Figure 3 compares vehicle speeds to the likelihood of severe injury or death to a pedestrian in an accident.
This data is taken from the US Department of Transportation, though multiple other agencies have
conducted comparable studies with similar results.
Figure 3. Pedestrian Injury Risk vs. Speed
It’s also important to note that other factors contribute to the level of risk, including the age of the
pedestrian.
Speed Limit Changes by Other Cities
New York City, NY
The statutory urban speed limit in the State of New York is 30 mph. In 2014, New York City lowered the
majority of local speed limits from 30 to 25 mph. Some quieter residential areas, or “slow zones” were kept
at 20 mph and some larger streets have speed limits higher than 25 mph.
Seattle, WA
The statutory urban speed limit in the State of Washington is 25 mph. in 2016, Seattle adopted a tiered
system for local speed limits; 25 mph for arterial streets and 20 mph for residential streets unless otherwise
signed. In addition, Seattle has been lowering speed limits on busier streets in recent years, piloting the use
of the 50th percentile speed rather than the 85th to set speed limits. Following implementation of these
changes on downtown streets, Seattle experienced a 13% reduction in total crashes and a 20% reduction in
fatal and serious injury crashes.
0 10 20 30 40 50 60 70 80 90
20
30
40
Likelihood of Severe Injury or Death, %Vehicle Speed, mph
REPORT / RECOMMENDATION Page 9
Portland, OR
The statutory urban speed limit in the State of Oregon is 25 mph. Portland has also implemented a tiered
system for local speed limits between 2016 and 2018; 15-25 mph for residential districts, 20 mph for school
zones, business districts and arterial streets and 15 mph for alleys. Changes made to local speed limits
require approval from the Oregon Department of Transportation.
Boston, MA
The statutory urban speed limit in the State of Massachusetts is 25 mph. In 2017, Boston lowered speed
limits citywide from 30 to 35 mph. A study conducted in 2018 by the Insurance Institute for Highway Safety
concluded that “lowering the speed limit in urban areas is an effective countermeasure to reduce speeds and
improve safety for all road users.”
Minneapolis/St. Paul, MN
Earlier this year, the Cities of Minneapolis and St. Paul announced plans to implement similar tiered systems
for local speed limits; 25 mph for major streets (mixed-use, commercial and downtown streets) and 20 mph
for minor streets (industrial and residential streets). Both cities intend for these changes to make streets
safer for all users and to support their Vision Zero goal of zero traffic deaths or severe injuries.
Local Traffic/Crash Analysis
Staff reviewed local traffic data collected between 2016 and 2019. This data was reviewed based on the
roadway classifications identified in the Living Streets Plan; Minor Arterial, Collector, Local Connector or
Local road (see Table 1).
Roadway
Classification
Average Daily
Traffic, vpd
Data
Points
85th Percentile
Speed Range, mph
Average 85th
Percentile Speed, mph
Minor Arterial 4,500 – 15,000 5 36.5 – 41.9 39.5
Collector 1,200 – 10,300 56 21.6 – 39.0 32.7
Local Connector 250 – 3,000 46 23.5 – 35.2 30.0
Local 30 – 1,200 64 17.9 - 32.5 25.4
Table 1: Local Traffic Analysis, 2016-2019
Relevant findings from this analysis include:
1. 85th percentile speeds tend to decrease as roadway classification and traffic volumes decrease.
2. The majority of drivers on Local and Local Connector roads obey the posted speed limit (most
of these roads are currently 30 mph).
3. Wider roads (Minor Arterials and Collectors) tend to have higher speeds than narrower roads
(Local Connectors and Locals).
REPORT / RECOMMENDATION Page 10
4. Highway frontage roads tend to have the highest recorded speeds (8 of the 10 highest observed
85th percentile speeds were on frontage roads adjacent to Highways 100, 169 and 494.
Crash data from the Minnesota Department of Public Safety was used to review local traffic accidents. This
analysis included reported accidents on County, Municipal State Aid and local roads in Edina over a 5-year
period between 2015 and 2019. Relevant findings from this analysis include:
1. Accidents were generally concentrated at intersections and along high-volume roads.
2. More than 50% of accidents on Municipal State Aid or local roads occurred at intersections.
3. Nearly all (96%) of accidents on Municipal State Aid or local roads occurred under a posted
speed limit of 30 mph.
4. Only one fatal crash was reported over this time period; a pedestrian was struck and killed on
France Avenue in 2016.
5. Proportionately, the severity of accidents was similar regardless of roadway type, with the
majority resulting merely in property damage (see Table 2).
Crash Severity Local Roads Municipal State Aid Roads County Roads
Property Damage 70.9% 67.9% 67.4%
Possible Injury 17.3% 16.9% 16.7%
Minor Injury 9.8% 13.6% 13.4%
Serious Injury 1.7% 1.4% 1.8%
Fatality - - 0.2%
Unknown 0.3% 0.2% 0.5%
Table 2. Local Crash Analysis, 2015-2019
6. Most accidents had no clear contributing action reported. Regardless of roadway type,
distracted driving, failing to yield the right-of-way, and running red lights were generally reported
more frequently than speeding.
7. Accidents involving pedestrians or cyclists were relatively rare (less than 10%) and generally
occurred along County or Municipal State Aid roads. The greatest concentration of these is in
the southeast quadrant of Edina, primarily along France Avenue and York Avenue.
8. Accidents involving a pedestrian or cyclist were more than three times as likely to result in a
minor or serious injury compared to overall crashes.
REPORT / RECOMMENDATION Page 11
Basis for Recommendation
Following review of the research and data included in this report, staff’s recommendation is based on the
following findings:
1. Lower speeds reduce the likelihood and severity of motor vehicle crashes.
2. Utilizing the 85th percentile to set speed limits prioritizes motor vehicle traffic over the safety of
all modes of transportation, including pedestrians and cyclists.
3. Lower speed limits promote public health and safety and support the goals established in the
Comprehensive Plan and Living Streets Plan.
4. A tiered approach to local speed limits is most appropriate for Edina given the wide range of
traffic volumes and percentage of non-local traffic on city streets. This approach is consistent
with that implemented by other cities that strive to accommodate all modes of transportation
(Minneapolis, Portland, Seattle and Boston).
Recommendations for City of Edina Speed Limits
Staff recommends a tiered approach to setting local speed limits in Edina. Table 3 summarizes the
recommended changes.
Category Recommended
Speed Limit, mph
Current Speed
Limit, mph
Percent of
Local Mileage
Major Streets – Arterial 30 30 – 40 7%
Major Streets - Collector 25 25 – 30 19%
Major Streets – Collector (School Zone) 20 20 1%
Minor Streets 20 30 72%
Minor Streets (School Zone) 15 15 1%
Alleys 10 10 -
Table 3. Summary of Recommended Speed Limit Changes
Major Streets – Arterial: These roads are categorized as Minor Arterials or Collectors in the Living
Streets Plan. They are generally four-lane Municipal State Aid roads with limited driveway access that
connect to County roads or State highways. The majority have no on-street parking, sidewalks on both
sides and carry transit service. Examples include West 50th Street between Grange Road and Wooddale
Avenue and West 78th Street between Gleason Road and Bush Lake Road.
Major Streets – Collector: These roads are categorized as Collectors or Local Connectors in the Living
Streets Plan. They are generally two-lane Municipal State Aid roads, highway frontage roads or roads within
commercial or industrial areas with medium-to-high driveway access. The majority have parking restricted
REPORT / RECOMMENDATION Page 12
on one or both sides, a sidewalk on at least one side and many carry transit service. Examples include
Olinger Blvd between Vernon Avenue and Tracy Avenue and West 66th Street between Ridgeview Drive
and Valley View Road.
Minor Streets: These roads are categorized as Local streets in the Living Streets Plan. They are generally
two-lane residential roads with high driveway access or roads within commercial districts that have high
pedestrian volumes. The majority have parking on both sides, no sidewalks and do not carry transit service.
Examples include Hansen Road between Vernon Avenue and Benton Avenue and Market Street between
Halifax Avenue and France Avenue.
School Zones: These are defined as portions of the street adjacent to school grounds where children have
access to the street. Seven of these zones currently exist in Edina, adjacent to Our Lady of Grace Catholic,
Highlands Elementary, Countryside Elementary, Normandale Elementary/Concord Elementary/South View
Middle, Creek Valley Elementary, Valley View Middle/Edina High, and Cornelia Elementary School. These
areas are proposed to remain at their existing 15- or 20-mph restrictions with a few minor changes to
further reduce speeds on other adjacent streets. One new 15-mph School Zone is recommended on
Inglewood Avenue, Grimes Avenue and West 42nd Street adjacent to Golden Years Montessori and Avail
Academy.
Alleys: These are public thoroughfares with less than 30 feet of allocated right-of-way. Section 169.14 of
the Minnesota Statutes and Section 26-7 of City Code currently restricts speed limits in alleys to no more
than 10 mph.
Figure 4 shows all recommended speed limits on local roads in Edina.
REPORT / RECOMMENDATION Page 13
Figure 4. Recommended Speed Limits
REPORT / RECOMMENDATION Page 14
The NTSB safety study previously mentioned in this report notes that “a comprehensive approach to
speeding typically involves multiple countermeasures.” Drivers are influenced by the geometric
characteristics of a roadway as well as the posted speed limit. In addition to these recommended speed
limits, staff recommends continuing to follow Living Streets design standards with pavement management
projects when feasible. These design standards include minimum roadway widths and reallocation of right-
of-way for pedestrian and bicycle infrastructure. Physical changes to roadways will complement the lowered
speed limits to reduce vehicle speeds and improve safety for all modes of transportation.
Coordination
Internal partners – Public Works, Police
External partners – Eden Prairie, Minnetonka, Hopkins, St. Louis Park, Minneapolis, Richfield, Bloomington,
Hennepin County, Metro Transit, Minnesota Department of Transportation
Next Steps
Communications and Education Plan
Signage Plan
Traffic Signal Plan
Enforcement Plan
Evaluation Plan and Future Modifications
Date: July 21, 2020 Agenda Item #: IV.
To:Mayor and City Council Item Type:
Other
From:Sharon Allison, City Clerk
Item Activity:
Subject:MOTION TO CLOSE SESSION: As permitted by
Minn. Stat. 13D.05 Subd. 3(b) for Attorney-Client
Privilege to Discuss Robert C. Tengdin, Trustee of
the Robert C. Tengdin Revocable Trust dated May
18, 2009 v. City of Edina
Action
CITY OF EDINA
4801 West 50th Street
Edina, MN 55424
www.edinamn.gov
ACTION REQUESTED:
Adopt motion as stated.
INTRODUCTION:
Date: July 21, 2020 Agenda Item #: V.
To:Mayor and City Council Item Type:
Other
From:Chad A. Millner, P.E., Director of Engineering
Item Activity:
Subject:Update on Robert C. Tengdin, Trustee of the Robert
C. Tengdin Revocable Trust dated May 18, 2009 v.
City of Edina
Information
CITY OF EDINA
4801 West 50th Street
Edina, MN 55424
www.edinamn.gov
ACTION REQUESTED:
None; information only.
INTRODUCTION:
Staff and legal counsel will provide an update on this lawsuit.
ATTACHMENTS:
Description
Study of Higher Water Levels at Highlands Lake and the East Basin, July 16, 2020
Barr Engineering Co. 4300 MarketPointe Drive, Suite 200, Minneapolis, MN 55435 952.832.2600 www.barr.com
Technical Memorandum
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020
1.0 Introduction
1.1 Study Purpose
In recent years, residents around Highlands Lake and the East Basin have noticed higher water levels in
both waterbodies, with water extending onto private property. In response to resident concerns about
higher water levels around Highlands Lake and the East Basin in the summer and fall of 2019, the City
requested that Barr Engineering Co. (Barr) conduct a study to evaluate the sources of the higher water
levels. This evaluation included surface water level and groundwater level monitoring in the fall of 2019, a
review of historical precipitation and groundwater data, and a review of the drainage area (both existing
and historical conditions). The study included the following tasks:
• surface water level and groundwater level monitoring in the fall of 2019,
• a review of historical precipitation and groundwater data,
• a review of the drainage area (both existing and historical conditions),
• water level computer simulations (water balance modeling).
• evaluation of concept-level mitigation options
1.2 Study Area and Drainage Pattern
The Highlands Lake watershed is a 276-acre watershed that is bordered on the north by Interlachen
Boulevard and portions of the Interlachen Country Club golf course. The Highlands Lake watershed land
use is characterized by residential areas, part of the Interlachen golf course, several ponding basins that
ultimately drain to Highlands Lake, a landlocked area directly east of the lake (East Basin), Highlands Park
(directly south of the lake), and a portion of the drainage from Highlands Elementary School.
Highlands Lake and the landlocked East Basin are separated by a large naturally formed berm, as shown in
Figure 1-1. A landlocked basin is a localized depression that does not have an outlet at or below its 1-
percent-annual-chance (100-year) flood elevation.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 2
P:\Mpls\23 MN\27\23271813 Confidential\WorkFiles\Tech Memo\Highlands_EastBasin_TechMemo_July16_2020.docx
Figure 1-1 Digital elevation model showing the elevation difference between Highlands Lake and the East Basin (gray lines are 2-foot topographic lines, and bold black lines are 10-foot topographic lines).
The stormwater system within and downstream of the Highlands Lake drainage area (Figure 1-2)
comprises storm sewers (including pumped lake outlets), ponding basins, wetlands, drainage ditches, and
overland flow paths. The water level of Highlands Lake is controlled by a pumped outlet. The pumped
outlet (lift station) was installed in 1994 and is located in the southwest corner of Highlands Park, near the
intersection of Ayrshire Boulevard and Glengarry Parkway and is also shown on Figure 1-2. Water from
the pumped outlet flows south, connecting with the storm sewer system along Vernon Avenue, which
discharges into Hawkes Lake.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 3
P:\Mpls\23 MN\27\23271813 Confidential\WorkFiles\Tech Memo\Highlands_EastBasin_TechMemo_July16_2020.docx
Figure 1-2 Storm sewer system from Highlands Lake to Nine Mile Creek.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 4
P:\Mpls\23 MN\27\23271813 Confidential\WorkFiles\Tech Memo\Highlands_EastBasin_TechMemo_July16_2020.docx
The Hawkes Lake watershed is a 336-acre watershed. There are several ponding basins within the
watershed that drain to Hawkes Lake via drainage ditches and storm sewer systems. Hawkes Lake also has
a pumped outlet. The pumped outlet, located on the west side of the lake near the intersection of Wycliffe
Road and Merold Drive, discharges southwest to the Mud Lake watershed. Section 5 of the City’s 2018
Comprehensive Water Resources Management Plan (CWRMP) (reference (1)) describes the potential
impacts to several principle structures (habitable homes) for a 1-percent-annual-chance flood under
existing conditions around Hawkes Lake.
Mud Lake is located just east of the North Fork of Nine Mile Creek, between TH 62 and Vernon Avenue.
The lake and surrounding wetlands are part of Bredesen Park. The Mud Lake watershed spans an area of
approximately 432 acres. The watershed has a complex drainage system and outlets to the North Fork of
Nine Mile Creek just north of Trunk Highway 62 through a culvert. As described in the City’s CWRMP
(reference (1)), a 1-percent-annual-chance flood in Mud Lake has the potential to inundate much of the
undeveloped area, including the trails surrounding Bredesen Park.
Due to the connectivity of Highlands Lake, Hawkes Lake, and Mud Lake, and the potential for flood
impacts to principle structures under existing conditions, any stormwater management changes made to
the Highlands Park area have the potential to adversely impact downstream areas and thus downstream
impacts resulting from any system alteration need to be assessed prior to implementation of any flood
mitigation option.
2.0 Review of the Historical Information
Barr’s review of historical information focused on a drainage area review, review of historical
climatological data, and review of historical groundwater data to evaluate potential sources of the higher
water levels observed in Highlands Lake and the East Basin. Summaries of each of these reviews are
presented in the following subsections.
2.1 Drainage Area Review
2.1.1 Drainage Conditions Summary
Review of storm sewer alignments and best available elevation (topography) data (reference (2)) indicates
that the drainage area to both Highlands Lake and the East Basin is dictated by topography (i.e., storm
sewer and stormwater conveyance infrastructure do not divert flow across topographical hydrologic
divides for storm events equal to or less than the 1-percent-annual-chance storm event). Drainage divides
(watershed divides) and storm sewer data can be viewed (along with topography data) on the City’s
publicly available water resources web map (reference (3)).
2.1.2 Historical Land Use and Development
Using historical aerial imagery, Barr evaluated the development of the Highlands Lake and East Basin
watersheds over time. Aerial photos from 1930 to 2018 are shown in Figure 2-1 through Figure 2-6.
Additionally, these figures include watershed divides developed based on 2011 elevation data (orange
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lines) and a line that represents a visual tracing of the historical tree line on Highlands Lake and the East
Basin (green line). This outline can indicate the separation between soils that are suitable for tree growth
and soils that are too wet for tree growth.
Significant development in the contributing watersheds (predominantly residential development)
occurred between 1950 and 1960. Using imagery for 1953 and 1960, the number of structures was
estimated in each watershed to determine the change over the decade. Additionally, a national
geographic information system (GIS) building layer published by Microsoft was used to count the number
of structures within the watersheds in 2018 to determine the change from 1960 to 2018. The approximate
number of structures for each watershed is listed in Table 2-1 by year. The number of structures for each
year is qualified as an approximate number due to inaccuracies that may be a result of low resolution
imagery (i.e., homes difficult to see in pixelated images) and unverified structure polygons in the Microsoft
building layer. In 1953, the Highlands Lake watershed had approximately 100 structures and the East Basin
watershed had approximately 30 structures. In 1960, the Highlands Lake watershed had approximately
170 structures (+70 from 1953) and the East Basin watershed had approximately 40 structures (+10 from
1953). In 2018, the Highlands Lake watershed had approximately 190 structures (+20 from 1960) and the
East Basin watershed had approximately 50 structures (+10 from 1960). These structure counts and the
visual comparison of the aerial imagery suggest that by 1960, approximately 88% of the development
(based on 1953 structures compared to 2018 structures) within the Highlands Lake and East Basin
watersheds had occurred (Figure 2-3). In recent years, Edina has seen an increase in residential
redevelopment, often characterized by tearing down a home and rebuilding a larger home. Residential
redevelopment is a permitted activity requiring review by the City’s staff. The rate of development and
redevelopment in recent years has decreased compared to the rate of development which occurred in the
1950s and 1960s (based on our structure counts).
Table 2-1 Approximate number of structures in the Highlands Lake and East Basin watersheds for 1953, 1960, and 2018
Year
Approximate # of
structures in Highlands
Lake watershed
Approximate # of
structures in the East
Basin watershed
Approximate total # of
structures in both
watersheds
1953 100 30 130
1960 170 40 210
2018 190 50 240
We also conducted a sensitivity analysis on imperviousness within the Highlands Lake and East Basin
contributing watersheds using the water balance model developed for Fall 2019 conditions (discussed in
detail in Section 4). For the Highlands Lake contributing watershed, we estimated the increase in
impervious area since 1953 to be approximately 13.5 acres (~32% increase in imperviousness from 1953
to 2018). When we decrease imperviousness by that same percentage (~32% reduction in impervious
area), the water level in Highlands Lake dropped 0.3 feet (3.6 inches). For the East Basin contributing
watershed, we estimated the increase in impervious area since 1953 to be approximately 2.85 acres (~55%
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increase in imperviousness from 1953 to 2018). When we decrease imperviousness by that same
percentage (~55% reduction in impervious area), the water level in the East Basin dropped 0.2 feet (2.4
inches).
The East Basin is classified as a Type 2 wetland in the City’s Comprehensive Water Resources Management
Plan (reference (1)). However, to our knowledge, an official wetland delineation has not previously been
conducted for the East Basin. Barr conducted the field work associated with a wetland delineation on
June 19, 2020, and is currently developing the associated report that will be submitted to the Minnesota
Board of Water and Soil Resources’ (BWSR’s) local government unit for review and approval related to the
regulatory provisions of Minnesota’s Wetland Conservation Act (WCA). In lieu of an official wetland
delineation, a desktop review using the historical aerial photos was conducted. The review identified an
approximate boundary of frequently wet or saturated areas for Highlands Lake and the East Basin based
on the visible tree line prior to development (the green line on Figure 2-1 through Figure 2-6). It appears
that most of the development in the area occurred outside or adjacent to the approximate delineation of
saturated areas. The two exceptions in the study area are the tennis court at 5241 Lochloy Drive (adjacent
to the East Basin) and the current playground area just south of Highlands Lake, which first appears on
historical aerial photos as a baseball diamond in Highlands Park. These developments were constructed
prior to any official rules about filling in wetlands (e.g., the Wetland Conservation Act, first passed in 1991
in Minnesota). The tennis court and playground area/baseball diamond were constructed in areas that
appear to have been wet and would have historically stored surface water (note that they both first
appear on the 1960 aerial photo, Figure 2-3).
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Figure 2-1 Highlands Lake and East Basin aerial imagery, 1940
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Figure 2-2 Highlands Lake and East Basin aerial imagery, 1953
Highlands
Watershed:
~100
structures
East Basin
Watershed:
~30 structures
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Figure 2-3 Highlands Lake and East Basin aerial imagery, 1960
Highlands
Watershed:
~170
structures
East Basin
Watershed:
~40 structures
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Figure 2-4 Highlands Lake and East Basin aerial imagery, 1975
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Figure 2-5 Highlands Lake and East Basin aerial imagery, 2002
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Figure 2-6 Highlands Lake and East Basin aerial imagery, 2018
Highlands
Watershed: ~190
structures
East Basin
Watershed:
~50 structures
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2.2 Historical Groundwater Data
Barr reviewed data from two nearby groundwater monitoring wells in the surficial aquifer to evaluate
changes and trends in groundwater levels in the years leading up to 2019. The two wells are located in
Edina (Nine Mile Creek Watershed District, NMCWD, Well #41) and Bloomington (Bloomington Hyland
Lake Park Preserve Well, MN DNR observation well #27077). NMCWD Well #41 is located within a few city
blocks of the study area and provides long-term groundwater data from near the Highlands Lake area.
MN DNR Observation well #27077 is located within the Hyland Lake Park Preserve in Bloomington. Data
from this well has been recorded continuously since 2016 and provides information on regional
groundwater response. At both wells, groundwater levels have been increasing in the past decade. At
NMCWD Well #41, groundwater levels have increased approximately 8 feet since 2010 (see Figure 2-7).
At MN DNR observation well #27077 in Bloomington, groundwater levels have increased approximately 5
feet in just the past 3 years (see Figure 2-8).
Figure 2-7 Groundwater levels at Nine Mile Creek Watershed District Well (#41) in Edina
874
876
878
880
882
884
886
2000 2001 2002 2004 2005 2006 2008 2009 2010 2012 2013 2015 2016 2017 2019Water Level (ft, NAVD88)Year
NMCWD Well 41
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Figure 2-8 Water table levels at Bloomington Hyland Lake Park Preserve Well (#27077) (Source: MN DNR Cooperative Groundwater Monitoring Database)
2.3 Climatological Data
Barr reviewed climatological data from the Minnesota Department of Natural Resources State Climatology
office as part of this study to evaluate changes and long-term trends in precipitation. As shown in Figure
2-9, the highest annual precipitation recorded at the Minneapolis-St. Paul International Airport was
recorded in 2019 and was nearly 8% higher than the next highest year (2016). Figure 2-9 shows the top 10
wettest years (most annual precipitation) for the Twin Cities using the Minneapolis-St. Paul International
Airport gage. It is worth noting that three of the years on this plot are within the past two decades (2002,
2016, and 2019), and the two highest years, 2016 and 2019, are very recent. The average annual
precipitation total for the Twin Cities (at the Minneapolis-St. Paul International Airport gage) is 30.6
inches. The driest year on record (1910) had a precipitation total of 11.5 inches.
751
752
753
754
755
756
757
758
759
1/1/2016 12/21/2016 12/11/2017 12/1/2018 11/21/2019Groundwater Elevation (ft, MSL)
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Figure 2-9 Top 10 wettest years in the Twin Cities (precipitation at Minneapolis-St. Paul International Airport; adapted from a Star Tribune article, 2019; 2019 data extended by Barr to include all of 2019)
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Figure 2-10 shows average annual precipitation totals for all precipitation gages within Hennepin County
(note Figure 2-9 is for MSP airport only) for the past 50 years, including 2019. In the past 50 years, there
has been an increasing trend in annual rainfall totals at a rate of 0.66 inches more precipitation per
decade.
Figure 2-10 Average annual precipitation for all Hennepin County gages from 1970 to 2019 (Source: MNDNR State Climatology Office)
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Figure 2-11 shows the average annual precipitation depth per decade from the end of the 19th century to
the 2010s at the Minneapolis-St. Paul International Airport gage. The 2010s are the wettest decade in
Minnesota’s history.
Figure 2-11 Average annual precipitation by decade at Minneapolis-St. Paul International Airport (Source: MNDNR State Climatology Office)
It is worth noting that the 1940s, 1950s, and 1960s were three consecutive decades with slightly less than
average precipitation. This was a prolonged period of relatively stable conditions when much of the
development in the study area occurred. Prior to this period, the 1930s was a drier decade; in fact, the
driest on record. From the 1960s on, there has been a clear trend in the total precipitation, both on an
annual basis (as shown in Figure 2-10) and by decade (as shown in Figure 2-11).
28.4
31.9
28.4 27.3 25.6
28.5 28.1 28.0 30.1 29.6
32.3 30.2
33.9
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
1890s 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010sAverage Annual Precipitation (inches)Decade
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Figure 2-12 shows the total monthly precipitation for 2019 compared to the average total monthly
precipitation (1938-2019) in the Twin Cities as reported at Minneapolis-St. Paul International Airport.
Figure 2-12 Monthly precipitation at Minneapolis-St. Paul International Airport (Source: MNDNR State Climatology Office)
Figure 2-13 through Figure 2-15 shows the 30-year average annual precipitation isoplots for Minnesota.
This is the time frame normally used to develop what is called a “climate normal” (i.e., average
precipitation over a recent 30-year period). Isoplots (or contour plots) show continuous lines where each
line represents a specific value, displaying how these values vary spatially. The precipitation isoplots show
specific total annual precipitation values and use color shading to indicate a gradient of precipitation
depths, where red is lower total annual precipitation and blue is higher total annual precipitation. The
bold line on these plots represents where there is 26 inches of total precipitation. Figure 2-13 shows the
30-year average precipitation depth for years 1895 to 1924, where the 26-inch contour runs
approximately through the middle of Minnesota from the southwest corner to the northern border. Figure
2-14 shows the 30-year average for years 1951 to 1980, with the 26-inch contour moving west. The
eastern half of Minnesota generally shows minor increases in precipitation totals. Figure 2-15 shows the
30-year average for years 1989–2018. In this final plot, the 26-inch contour has moved into the
northwestern quadrant of Minnesota and the southeastern portion of the state (including the Twin Cities
metro area) shows significantly higher average annual precipitation depths. Figure 2-15 also indicates
0
1
2
3
4
5
6
7
8
Precipitation (inches)Average Monthly Precip (1938-2019)2019 Monthly Precip
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where the 26-inch contour for 1924 was located, showing its migration farther northwest over the span of
almost a century.
Figure 2-13 30-year average annual precipitation isoplots for the state of Minnesota (Source: Kenneth Blumenfeld, MNDNR State Climatology Office)
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Figure 2-14 30-year average annual precipitation isoplots for the state of Minnesota (Source: Kenneth Blumenfeld, MNDNR State Climatology Office)
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Figure 2-15 30-year average annual precipitation isoplots for the state of Minnesota (Source:
Kenneth Blumenfeld, MNDNR State Climatology Office)
While the data presented earlier in this section refers to historical data, the National Weather Service
recently (March 2, 2020) conducted a webinar presentation titled “2020 Spring Flood Outlook (Covering
Central/Southern Minnesota and Western Wisconsin).” The presentation provided an overview of the
flood potential for spring 2020, reviewed flood factors (soil moisture, frost depth, base water levels,
snowpack, spring weather/precipitation), and provided a summary of long-range weather trends. At the
conclusion of the presentation, the presenter stated the following: “due to the long duration of wetter-
than-normal conditions, area lakes, wetlands, ponds, ditches, and even groundwater are running
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exceptionally high. Flooding of lakes, ponds, lowlands, fields has a high probability of occurring even with
normal rainfall this spring.”
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3.0 Site Visit and Monitoring
3.1 Site Visit
Barr staff and City staff conducted a site visit of Highlands Lake and the East Basin on September 24, 2019,
to better understand the impacts of the higher water levels in both basins on the surrounding properties.
3.2 Surface Water and Groundwater Monitoring
Surface water monitoring data were collected throughout the fall of 2019 at both Highlands Lake and the
East Basin. Groundwater level readings were also collected throughout the fall of 2019 using piezometers
located adjacent to both Highlands Lake and the East Basin as shown on Figure 3-2. Surface-water-level
data loggers were installed on September 10, 2019 to measure fluctuations of the water levels in
Highlands Lake and the East Basin, and an additional data logger was installed in the open atmosphere to
correct for barometric pressure changes.
During the monitoring period, several maintenance activities were performed on the Highlands Lake lift
station that impacted subsequent Highlands Lake water levels shown in our monitoring data:
• October 2, 2019: pump well was cleaned and pump frequency increased from 54 to 60 Hz
• October 3, 2019: pump frequency lowered back down from 60 to 56 Hz
• October 10, 2019: outlet pipe from pump cleaned (jetted)
• October 21, 2019: pump turned on automatically; pump frequency lowered from 56 to 54 Hz
Additionally, as it relates to monitored lake levels, on October 16, the pump turned off automatically when
it had drawn the lake level down to approximately the normal water level. Significant rain on October 21
and October 22 caused the lake level to rise and the pump to turn back on, as expected. Finally, the pump
automatically turned off again on October 26 when the lake level went back down again.
Surface water level monitoring results are shown on Figure 3-1, along with the changes in pump
operation during the monitoring period. Water levels in both Highlands Lake and the East Basin generally
decreased from the beginning to the end of the monitoring period, with periodic water level increases
during storm events (Figure 2-13). It should be noted that the months preceding the monitoring period
(July and August) received an excessive amount of rainfall. The pump well cleaning on October 2
increased the drawdown rate of Highlands Lake, but minimal change in drawdown rate was seen in the
East Basin. The Highlands Lake water elevation showed a slow and steady rise while the lift station was off
in mid-to-late October.
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Figure 3-1 Surface water monitoring results with precipitation and notes on pump operation (green triangles represent dates when changes were made impacting the pump operation).
To monitor groundwater, four piezometers were installed on October 3, 2019, at the locations shown in
Figure 3-2: one west of Highlands Lake, two on the earthen berm between Highlands Lake and the East
Basin, and one east of the East Basin. Manual measurements of water levels within each piezometer were
taken on October 3, November 1, and November 18, 2019. All monitoring equipment was removed on
November 18, 2019; the piezometers were left in the ground for potential future monitoring.
Well cleaned (imp. performance), 54 to 60 Hz
Lowered 60 to 56 Hz
12" pipe jetted (little impact)
Pump OFF Pump On. 56 to 54 Hz.
Pump OFF
Pump On
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0887.0
888.0
889.0
890.0
891.0
892.0
893.0
894.0
Daily Precipitation (inches)Elevation (NGVD29, feet)Date
Highlands Lake Monitored Water Surface Elevation (NGVD29)
East Basin Monitored Water Surface Elevation (NGVD29)
Highlands Pump Operation Notes
Precipitation
Highlands Lake Outlet Elevation
Estimated post-cleanoutpump rate from water balance: 315 gpm
Estimated pre-cleanoutpump rate from water balance: 180 gpm
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Figure 3-2 Installed piezometer locations
Readings from the piezometers on October 3, 2019, and November 18, 2019, are plotted on a cross
section of Highlands Lake and the East Basin in Figure 3-3 and Figure 3-4. The water levels from
November 18 are not plotted separately because the readings on November 1 and November 18 were
almost indistinguishable. In October and November, the surface water level in Highlands Lake was 2.5
feet and 1.7 feet higher, respectively, than the water level in the East Basin. Hydraulic gradients between
groundwater and surface water indicate groundwater is likely flowing into Highlands Lake on the north
and west shorelines. The water level difference between PZ-01 and Highlands Lake was 1.07 feet on
October 3, 2019 and 1.67 feet on November 18, 2019. Water level differences indicate a potential for flow
from surface water to groundwater on the east shoreline of Highlands Lake. The water level difference
between PZ-02 and Highlands Lake was -0.06 feet and -0.02 feet on October 3 and November 19, 2019,
respectively. However, potential accuracy with water level measurement and the elevation survey result in
the water level differences on the east side being inconclusive.
Similar to Highlands Lake, water level differences between East Basin and groundwater indicate potential
for groundwater inflow from the west shore and flow from East Basin to groundwater on the east/south
side. The water level difference between PZ-03 and East Basin was 0.06 feet on October 3, 2019 and 0.11
feet on November 18, 2019. The water level difference between PZ-04 and East Basin was -0.17 feet and
-0.06 feet on October 3rd and November 19, 2019, respectively. The magnitude of these water level
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differences is small and within the measurement accuracy. However, water balance modeling (see Section
4.0) supports a net groundwater loss for East Basin and net groundwater gain for Highlands Lake, which is
consistent with these data given the measurement accuracy.
3/8”
1/4”
1/4”
1/4”
SAND AND GRAVEL
BEDROCKBEDROCK
PEAT
FILL
SAND AND GRAVEL
PEAT
FILL
ASOUTH A'NORTH
MW-1PZ-5PZ-3SB-6Elevation, Feet (MSL)6pt Arial
8pt Arial Italic
Soil classifications - ALL CAPS 8pt ArialAll other text - Caps and Lower Case 8pt Arial
11pt Arial Bold
9pt Arial
11pt Arial
8pt Arial
8pt Arial
8pt Arial
2.0 Th
.6 Th
.75 to 1.0 Th
Update horziontal scale every timeUpdate vertical scale every timefilepath does NOT auto update890
895
900
905
885
880
875
890
895
900
905
885
880
875Elevation (ft msl)(NGVD29)Elevation (ft msl)(NGVD29)LEGEND
Ground Surface
Approximate Bathymetry
Groundwater Level (October 3, 2019)
Piezometer Screen
Soil Boring/Piezometer
Surface water level (October 3, 2019)
0 150
Approximate Horizontal Scale in Feet30X Vertical Exaggeration
Figure 3-3GEOLOGIC CROSS SECTION Highlands Lake and East Basin City of Edina
880
885
890
895
900
905
0 200 400 600 800 1000 1200 1400 1600 1800 2000Eleva�on (feet), NGVD29Sta�on (feet)
LiDAR Well PZ-01 Well PZ-02 Well PZ-03 Well PZ-04 Highlands WL Oct04
East Basin WL Oct04 PZ-01 WL Oct04 PZ-02 WL Oct04 PZ-03 WL Oct04 PZ-04 WL Oct04 Approximate BathymetryMirror Lakes DriveHighlands Lake East Basin
PZ-01PZ-02PZ-03PZ-04PZ-04PZ-03PZ-02PZ-01HIGHLANDS LAKE
Water Surface Elevation = 890.0 ft
Oct. 3, 2019
EAST BASIN
Water Surface Elevation = 887.5 ft
Oct. 3, 2019Mirror Lakes DriveWEST EAST
12-inch PVC to Lift Station
887.3 ft887.6 ft
889.9 ft
891.0 ft
3/8”
1/4”
1/4”
1/4”
SAND AND GRAVEL
BEDROCKBEDROCK
PEAT
FILL
SAND AND GRAVEL
PEAT
FILL
ASOUTH A'NORTH
MW-1PZ-5PZ-3SB-6Elevation, Feet (MSL)6pt Arial
8pt Arial Italic
Soil classifications - ALL CAPS 8pt ArialAll other text - Caps and Lower Case 8pt Arial
11pt Arial Bold
9pt Arial
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2.0 Th
.6 Th
.75 to 1.0 Th
Update horziontal scale every timeUpdate vertical scale every timefilepath does NOT auto update890
895
900
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885
880
875
890
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875Elevation (ft msl)(NGVD29)Elevation (ft msl)(NGVD29)LEGEND
Ground Surface
Approximate Bathymetry
Groundwater Level (November 1, 2019)
Piezometer Screen
Soil Boring/Piezometer
Surface water level (November 1, 2019)
0 150
Approximate Horizontal Scale in Feet30X Vertical Exaggeration
Figure 3-4GEOLOGIC CROSS SECTION Highlands Lake and East Basin City of Edina
880
885
890
895
900
905
0 200 400 600 800 1000 1200 1400 1600 1800 2000Eleva�on (feet), NGVD29Sta�on (feet)
LiDAR Well PZ-01 Well PZ-02 Well PZ-03 Well PZ-04 Highlands WL Oct04
East Basin WL Oct04 PZ-01 WL Oct04 PZ-02 WL Oct04 PZ-03 WL Oct04 PZ-04 WL Oct04 Approximate BathymetryMirror Lakes DriveHighlands Lake East Basin
PZ-01PZ-02PZ-03PZ-04PZ-04PZ-03PZ-02PZ-01HIGHLANDS LAKE
Water Surface Elevation = 889.1 ft
Nov. 1, 2019 EAST BASIN
Water Surface Elevation = 887.4 ft
Nov. 1, 2019Mirror Lakes DriveWEST EAST
12-inch PVC to Lift Station
887.4 ft887.6 ft
889.1 ft
890.8 ft
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 29
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4.0 Water Balance Modeling
4.1 Water Balance Inputs
A continuous daily water balance model was developed for both Highlands Lake and the East Basin. The
model uses daily inflows and outflows to compute a net change in water volume and water surface
elevation for each basin. Inputs to the water balance included precipitation, runoff (as a function of
imperviousness), net groundwater inflow/outflow, evaporation/transpiration, pumping (in Highlands Lake
only), and basin storage. In order to calibrate a water balance model, the input parameters are adjusted
until the modeled water levels align with the daily average observed water levels as closely as possible.
The data formats and sources are described for each variable below.
Due to the proximity of Interlachen Golf Course and potential concerns about changes to irrigation
practices impacting surrounding waterbodies, City staff contacted Interlachen Country Club management
who reported no changes to irrigation operations during the 2019 season.
4.1.1 Precipitation
Barr used precipitation in 1-hour intervals from the Minneapolis-St. Paul International Airport to compute
daily precipitation (reference (4)). This precipitation depth was applied directly to the water surface area of
the basins to estimate daily volumes of precipitation inflow, and was used to calculate daily runoff
volumes from the tributary areas as described in Section 4.1.2.
4.1.2 Runoff
Watershed runoff as an inflow was calculated as a fraction of daily precipitation from both pervious and
impervious areas for each basin using the watershed area, impervious area, and runoff coefficients of 0.9
and 0.05 for impervious and pervious areas, respectively using the Simple Method (reference (5)). The
watershed area contributing to each water body was from the City’s CWRMP (reference (1)) XP-SWMM
(Stormwater Management Model) modeling. Impervious area was originally based on the City’s XP-
SWMM stormwater management model (reference (6)), corrected to not account for the impervious area
of the open water body itself (direct precipitation depth applied to the water body surface is converted to
runoff as described in Section 4.1.1). Impervious area was then adjusted within the water balance to
calibrate observed runoff volumes associated with rainfall events throughout the monitoring period as
described below:
• Water body stage monitoring data (Section 3.2) shows the stage response to rainfall events
throughout the monitoring period.
• The same day increase in stage was used to calculate the runoff volume generated from the
rainfall event.
• Impervious area within the water balance was adjusted as needed to calibrate modeled runoff
volumes to runoff volume calculated from observed monitoring data.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 30
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The imperviousness estimate was reduced from what was in the city’s XP-SWMM model as expected
because the model was developed to have slightly conservative (slightly high) imperviousness estimates.
4.1.3 Evaporation/Transpiration
Monthly evaporation rates from the University of Minnesota Climatology Working Group were converted
to daily rates in the water balance as an outflow from the water bodies (reference (7)). A pan coefficient
of 0.8 was applied to all pan evaporation data to calibrate monthly drawdown during periods of no
rainfall. Typical pan coefficients used for estimating lake drawdown range from 0.6 to 0.9 (Reference (8)).
Monthly transpiration rate estimates were taken from the White Oaks feasibility study nearby in the City
of Edina (reference (8)).
4.1.4 Groundwater
Groundwater exchange (net inflow or outflow of groundwater) was used as an adjustment factor in the
water balance. As described in Section 4.2, the impacts of groundwater exchange can be observed in
periods of no rainfall. For example, during periods where the Highlands Lake pump was not operating and
there was no observed rainfall (e.g., dates after 10/26/19, see Figure 3-1), the observed stage in Highlands
Lake continues to rise over time, while the observed stage in East Basin begins to fall. The rate of rise in
Highlands Lake likely indicates the presence of groundwater inflow in excess of evapotranspiration losses.
Conversely, the rate of stage decrease in East Basin is in excess of predicated evapotranspiration losses
and therefore likely indicates net outflow to groundwater. The trends in groundwater exchange used to
develop the water balance (i.e., new inflow of groundwater to Highlands Lake, net outflow to groundwater
from East Basin) are supported by groundwater levels observed and displayed in Figure 3-3 and Figure
3-4.
4.1.5 Pumping
Surface water from Highlands Lake is conveyed to a lift station (i.e., pump) at the southwest corner of
Highlands Park via a 12-inch-diameter 1,105-foot long gravity storm sewer pipe. The lift station operates
using a variable frequency drive, causing pumping rates to be variable based on the motor speed. The
level to which the lift station can draw down Highlands Lake is dependent both on the set motor speed
and the rate at which water can flow into the 12-inch pipe. The pump is meant to draw down the lake to
an approximate elevation (~889.0 ft, NAVD88) and then automatically shut-off until water levels begin to
rise again. The lift station pumps stormwater to a storm sewer system that ultimately discharges into
Hawkes Lake.
As described in Section 4.1.4, during extended periods where the Highlands Lake lift station was not
operating and no rainfall occurred, stage in Highlands begins to rise, indicating a net inflow of
groundwater in excess of evapotranspiration losses. As shown in Figure 3-1, during periods where the
Highlands Lake lift station is operational, lake stage begins to decrease during periods of no rainfall. By
comparing the rate of drawdown to groundwater inflow and evapotranspiration rates calculated during
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 31
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periods of no rainfall (Sections 4.1.3 and 4.1.4), the Highland Lake lift station pumping rate can be
calculated.
During the monitoring period, several maintenance activities were performed on the Highlands Lake
pump (see Section 3.2). To represent these activities in the water balance, two different pumping rates
were calculated: a lower pumping rate prior to well cleanout (October 2, 2019), and a higher pumping rate
post-well cleanout. No pumping was modeled for the time periods when the pump was off as recorded
by City operational staff (October 16 to October 21; October 26 to end of modeled period).
The modeled pumping rates were validated by reviewing the Highlands Lake pump operation curves
(reference (10)). The pump operation curves show that the pump will discharge below 400 gallons per
minute (gpm) at 54 Hz when the system is clean and operating well, which is close to the post-cleaning
discharge rate used to calibrate the water balance (315 gpm as shown on Figure 3-1). Prior to the pump
cleaning, the condition of the lift station was such that pump performance curves are not useful except to
understand the upper end of the pump capacity.
4.1.6 Storage
The stage-area relationship for Highlands Lake and East Basin was used to calculate the stage-storage
relationships for both water bodies. These relationships were taken from the City’s XP-SWMM model that
supported the CWRMP (reference (1)).
4.2 Water Balance Calibration
The water balance models for Highlands Lake and East Basin were calibrated to the surface water
monitoring data from September to November 2019. Three model input parameters were used for
calibration: imperviousness, groundwater exchange (net gain or loss), and the pump out rate for
Highlands Lake only. These parameters were adjusted until the modeled water levels aligned as closely as
possible to the daily average observed water levels throughout the monitoring period.
As described in Sections 4.1.2 through 4.1.5, calibration parameters were temporarily isolated during
times of rainfall and no rainfall as outlined below:
• Monthly evaporation and transpiration rates were calculated as described in Section 4.1.3, using
the same assumptions and source data for both Highlands Lake and the East Basin.
• During periods of no rainfall and no pumping, groundwater inflow/outflow was calibrated to
match observed rise/decline in observed stage.
• Highlands Lake Only: During periods of no rainfall when the pump was active, the pumping rate
was calculated by comparing the rate of lake drawdown to the rate of inflow and outflow from
other fixed sources (i.e., groundwater and evapotranspiration).
• During periods of rainfall, watershed impervious area was calibrated to match observed runoff
volumes (i.e., observed increase in stage associated with rainfall events).
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As described in Section 4.1.4, calibrating the water balance for the East Basin required a net outflow to
groundwater, with two rates specified: one earlier in the monitoring period while Highlands Lake water
levels were higher and one later as Highlands Lake was drawn down. The required groundwater outflow
rates utilized in the water balance are on the order of magnitude of monthly evapotranspiration losses
(e.g., for August, daily evapotranspiration loss is 0.38 in/day, and groundwater loss is 0.08 in/day).
The modeling of Highlands Lake required a net inflow from groundwater. As described in Section 4.1.4,
during periods where the Highlands Lake pump was not operating and there was no observed rainfall
(e.g., dates after 10/26/19, see Figure 3 1), the observed stage in Highlands Lake continues to rise over
time, indicating the rate of groundwater inflow to the lake is greater than evapotranspiration rates during
this period. This calibration parameter is also supported by groundwater monitoring data, which shows
that groundwater levels adjacent to the lake are higher than the lake level during both monitoring events
(Figure 3-3 and Figure 3-4).
The final calibrated water balance model inputs for Highlands Lake and East Basin are summarized in
Table 4-1.
Table 4-1 Final water balance parameters
Parameter Highlands Lake East Basin
Watershed Area (acres) 210.5 39.9
Imperviousness (acres, %) 42.1, 20% 5.2, 13%
Groundwater Gain/Loss (inches/day) Gain: 0.06 Loss (before October 2): 0.08
Loss (after October 2): 0.13
Pumping (gpm)
Before October 2 pump
well cleaning: 180 gpm
After October 2 pump
well cleaning: 315 gpm
--
Evaporation/Transpiration Rates (inches/day)
September 0.11/0.15
October 0.07/0.05
November 0.04/0.00
The water balances for Highlands Lake and East Basin matched the observed surface water monitoring
data well. The coefficient of determination (R2) for the Highlands Lake calibration is 0.97 (Figure 4-1) and
the R2 for the East Basin calibration is 0.92 (Figure 4-2).
Once the water balances were calibrated to the observed monitoring data, the calibration parameters
were used to project the water balance results back to August 1, 2019 (about one month prior to the start
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of the monitoring period). This was done to provide a slightly longer time series for evaluating potential
mitigation options.
Figure 4-1 Highlands Lake calibrated water balance
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Figure 4-2 East Basin calibrated water balance
5.0 Concept-Level Mitigation Options
Barr evaluated several concept-level mitigation options that could potentially help prevent Highlands Lake
and the East Basin waters from extending onto private property. These mitigation options are described in
the subsequent sections. It is important to note that modeling of potential mitigation options is based
only on fall 2019 conditions (i.e., modeling of mitigation options utilizes the fall 2019 water balance and
associated assumptions). The results presented below demonstrate the impact of mitigation options
during the monitoring period so that a direct comparison to observed fall 2019 conditions can be made.
Variable precipitation and groundwater inflow dynamics can impact the results of the potential mitigation
option modeling results presented in the following sections; therefore, we recommend longer surface
water and groundwater monitoring before pursuing long-term mitigation options.
5.1 Maintenance of Highlands Lake Pump Operation
One mitigation option is more frequent maintenance of the Highlands Lake lift station and inlet and
outlet pipes to ensure it is clean and operating at its designed capacity. At the beginning of the
monitoring period the pump was operating at a rate of about 180 gpm due to clogging and accumulation
of debris. After performing maintenance on the lift station, its operating rate increased to about 315 gpm.
This difference alone in the pumping rate (135 gpm) could account for an additional decrease of nearly
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0.5 feet per week in the water level of Highlands Lake. This is shown in Figure 5-1 from 8/1/2019 to
8/8/2019.
Barr ran the water balance models with a pumping rate of 315 gpm (i.e., the post-well cleaning pumping
rate) for the entire monitoring period. The effect on Highlands Lake water levels is shown in Figure 5-1. If
water levels are decreased in Highlands Lake, we may also expect the groundwater gradient between
Highlands Lake and the East Basin to decrease. This was modeled with the East Basin water balance by
increasing the groundwater net loss rate to 0.13 inches per day for the entire monitoring period. As
shown in Table 4-1, 0.13 inches per day was the estimated rate of loss from the East Basin late in the
monitoring period when Highlands Lake was low. The results for the East Basin are shown in Figure 5-2.
Overall, the water level in Highlands Lake decreases by approximately 1 foot through September and by
approximately 0.2 feet in the East Basin in late fall.
Figure 5-1 Highlands Lake water levels for maintained Highlands Lake outlet pump
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 36
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Figure 5-2 East Basin water levels for maintained Highlands Lake outlet pump
5.2 Floodwall
Another option for protecting private property around the East Basin is a floodwall. Two approaches were
considered: (1) a floodwall constructed at the private property boundary for impacted properties on the
south side of the East Basin (note the property boundaries fall within the basin itself), and (2) a wall built
on private property immediately adjacent to or around the features of most importance (e.g., tennis court
or gardens). The first approach would require either large amounts of fill behind the wall to create long-
term positive drainage to the East Basin or a drainage collection and pump system. The second approach
would be easier to construct and would require less fill.
However, given the proximity of these private features to the East Basin, there may be permitting
challenges. It is our understanding that the MNDNR does not have jurisdiction over the East Basin
because it is not listed as a public water. However, the Nine Mile Creek Watershed District does have
jurisdiction and wetland buffer requirements would apply—averaging 20 feet from the delineated wetland
boundary. Larger buffers may be required depending on the value of the wetland (up to an average of 60-
feet for high value wetlands). Unless a variance was granted, these buffer requirements likely make it
infeasible to construct a floodwall to protect features like the tennis court or private gardens on private
property adjacent to the East Basin.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 37
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In addition, floodwall design would require determining the appropriate height to protect private
property. Since the East Basin is landlocked (no storm sewer outlet), water levels vary; if water levels
continue to increase, it will be difficult to anticipate the appropriate flood wall elevation.
5.3 Pumping the East Basin
To protect private property along the south side of the East Basin, a small submersible pump could be
installed to pump water from the East Basin to Highlands Lake (likely via the street if approved by the
City). It would act much like a sump pump that is automatically triggered on and off. Based on the
conditions experienced in Fall 2019, a small pump, pumping at a rate of approximately 20 gpm, was
modeled as an outflow from the East Basin and an inflow to Highlands Lake. In the East Basin water
balance, the starting water surface elevation was assumed to be 886.5 feet. This is when the pump would
turn on to protect the tennis court at 5241 Lochloy Drive. The remaining model parameters (hydrology,
precipitation, etc.) remained the same. For this evaluation, the pump in Highlands Lake was assumed to
have been operating at its intended capacity, rather than the way it ran in 2019, before maintenance.
The results of this alternative are shown in Figure 5-3 and Figure 5-4. Assuming conditions similar to Fall
2019, this option does achieve the goal of keeping water off private property around the East Basin.
However, surface water and groundwater levels should continue to be monitored to ensure that a
pumping rate of 20 gpm is sufficient under other conditions. For example, higher groundwater levels or
years with even more total precipitation may necessitate a higher pumping rate. The 20-gpm pumping
scenario evaluated for Fall 2019 conditions was found to not increase flood impacts in downstream
waterbodies (i.e., Hawkes Lake and Mud Lake). However, if higher pumping rates and more-frequent
pumping is required based on future hydrologic conditions, the downstream impacts of pumping from
East Basin would need to be reevaluated.
In addition, Barr understands that the City has a policy of prioritizing flood mitigation projects for areas
where flooding threatens principle (habitable) structures. There are a substantial number of principle
structures at risk of flooding in the City. Within subwatershed HI_13, which includes the East Basin, the
City is unaware of any principle structures impacted by high water levels. As a result, this area does not fit
within the City’s flood mitigation project policy at this time. We also understand that the City considers
the policies outlined in the 2018 CWRMP when evaluating flood mitigation projects, including policies
prohibiting alterations of wetlands.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 38
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Figure 5-3 East Basin water levels: pumping from East Basin to Highlands Lake with 20 gpm pump
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 39
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Figure 5-4 Highlands Lake water levels: pumping from East Basin to Highlands Lake with 20 gpm pump, assuming the Highlands Lake pump is maintained (see Section 5.1).
5.4 Diversion of Drainage Area from East Basin to Highlands Lake
Barr reviewed the City’s utility information and determined that storm sewer to the north and east of the
East Basin could potentially be directed to Highlands Lake. Therefore, we evaluated an option to redirect
some stormwater away from the East Basin and into Highlands Lake. The existing storm sewer
infrastructure serves approximately 13.2 acres of drainage area to the East Basin. The water balance
models were run to simulate the removal of 13.2 acres from the East Basin’s watershed and the addition
of the same area to Highlands Lake’s watershed. These results are shown in Figure 5-5 and Figure 5-6.
Diverting area from the East Basin to Highlands Lake results in relatively minor differences in the water
levels of each water body (again, based only on Fall 2019 conditions).
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 40
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Figure 5-5 Highlands Lake water levels for diversion of 13.2 acres from East Basin to Highlands Lake watershed
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 41
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Figure 5-6 East Basin water levels for diversion of 13.2 acres from East Basin to Highlands Lake watershed, East Basin starting elevation 886.5 ft (NGVD29)
0.0
1.0
2.0
3.0
4.0
5.0
6.0885.0
886.0
887.0
888.0
889.0
7/14/2019 8/3/2019 8/23/2019 9/12/2019 10/2/2019 10/22/2019 11/11/2019 12/1/2019 Daily Precipitation (inches)Water Level (NGVD29 feet)Date
Modeled Water Level Observed Water Level
Calibrated Model Water Surface Tennis Court Elevation
Footpath Elevation Observed Precipitation (in.)
East Basin
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 42
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6.0 Summary of Key Findings
The key findings of the study are summarized below based on the details provided previously in this
memorandum:
1. Precipitation totals have been increasing in the Twin Cities area for decades. The total
precipitation in 2019 was the highest amount of annual precipitation on record. Water levels,
particularly in a landlocked basin like the East Basin, are substantially affected by extended
periods of high precipitation. The recent years of high precipitation and record-breaking
precipitation in 2019 are likely having a significant impact on the water levels in the study area.
2. Regional groundwater levels have increased by multiple feet in the last decade. Measurements at
the Nine Mile Creek Watershed District groundwater monitoring well, within a few city blocks of
the study area, show that nearby groundwater levels have increased approximately 8 feet since
2010. High groundwater levels are likely due to a number of factors, such as a long recent period
of increased precipitation and subsequent recharge to groundwater. High groundwater can result
in increases to inflows to lakes and ponds, which appears to be the case for Highlands Lake where
water balance modeling and groundwater level measurements suggest gains from groundwater.
In the case of the East Basin where water balance modeling suggests losses to groundwater, high
groundwater can also result in decreased outflow.
3. Surface water level monitoring and associated water balance modeling helped determine that the
Highlands Lake pumped outlet was not operating at its intended capacity when monitoring
began in the summer of 2019. After cleaning of the sump, the outflow rate from the lake
increased. Additionally, the modeling work showed that the pumped outlet rate had a significant
impact on water levels in Highlands Lake. Regular maintenance of critical infrastructure such as
this lift station is imperative for mitigating flood risk around Highlands Lake.
4. For the East Basin, a landlocked basin with no storm sewer outlet, based on the information
reviewed, we have not seen any conclusive evidence that any acts by the City impacted water
levels. We also understand that City staff recently inspected the East Basin and reported there
was minimal sedimentation and no evidence that the sedimentation is impacting the functionality
of the wetland.
5. The drainage area to Highlands Lake and the East Basin were largely undeveloped in 1940.
Development had begun by 1953, and by the 1970s the drainage area was nearly as developed as
it is today (with respect to number of homes and roads). In recent years, Edina has seen an
increase in residential redevelopment, often characterized by tearing down a home and rebuilding
a larger home. Residential redevelopment is a permitted activity requiring review by City staff.
While redevelopment can increase impervious area on a property, the rate of development and
redevelopment in recent years has decreased compared to the rate of development which
occurred in the 1950s and 1960s.
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 43
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6. In lieu of an official approved wetland delineation (currently in progress), a desktop review using
historical aerial photos was conducted. The review identified an approximate boundary of
frequently wet or saturated areas for Highlands Lake and the East Basin based on the visible tree
line prior to development. It appears that most of the development in the area occurred outside
or adjacent to the approximate delineation of saturated areas. The two exceptions are the tennis
court at 5241 Lochloy Drive (adjacent to the East Basin) and the current playground area just
south of Highlands Lake, which appears on historical aerial photos as a baseball diamond in
Highlands Park. These developments were constructed prior to any official rules about filling in
wetlands (e.g., the Wetland Conservation Act, first passed in 1991 in Minnesota). The tennis court
and playground area/baseball diamond were constructed in areas that appear to have been wet
and would have historically stored surface water.
7. Related to potential concept-level mitigation options, while the Minnesota Department of Natural
Resources (MNDNR) does not have jurisdiction over the East Basin, Nine Mile Creek Watershed
District (NMCWD) does, and wetland buffer rules will most likely apply to any mitigation projects
around the East Basin.
8. We recommend additional surface water and groundwater monitoring and water balance
modeling before implementing any mitigation measures (monitoring was restarted in June of
2020).
To: Chad Millner, City of Edina From: Sarah Stratton, Cory Anderson, Michael McKinney, and Tyler Olsen, Barr Engineering Subject: Study of Higher Water Levels at Highlands Lake and the East Basin Date: July 16, 2020 Page: 44
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7.0 References
1. Barr Engineering Co. City of Edina 2018 Comprehensive Water Resources Management Plan. Edina,
MN : s.n., July, 2018.
2. Minnesota Geospatial Commons. LiDAR Elevation, Twin Cities Metro Region. [Electronic Data]
Hennepin County : s.n., 2011.
3. City of Edina. Lakes, Ponds, Creeks, and Wetlands. [Online] [Cited: February 22, 2020.]
https://www.edinamn.gov/369/Lakes-Ponds-Creeks-and-Wetlands.
4. Iowa State University - Iowa Environment Mesonent. MSP 1-hour Precipitation. s.l. : ASOS Network,
November 6, 2019.
5. Schueler, T. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban Best
Management Practices. Washington D.C. : MWCOG, 1987.
6. Barr Engineering Co. City of Edina Imperviousness Assumptions for Stormwater Modeling. October 25,
2016.
7. Minnesota Department of Natural Resources. Monthly Pan Evaporation - U. of M. St. Paul Campus.
2019.
8. Dadaser-Celik, Filiz and Stefan, Heinz G. Lake Evaporation Response to Cimate in Minnesota. s.l. :
University of Minnesota St. Anthony Falls Laboratory, 2008.
9. Barr Engineering Co. STS-406 Improvement Project Part 3: Project Area 8-White Oaks. March 27, 2015.
10. FLYGT (a xylem brand). Technical Specification for Flygt 3127, 60 Hz.
Date: July 21, 2020 Agenda Item #: VI.
To:Mayor and City Council Item Type:
Other
From:Sharon Allison, City Clerk
Item Activity:
Subject:Motion to move back into Open Session Action
CITY OF EDINA
4801 West 50th Street
Edina, MN 55424
www.edinamn.gov
ACTION REQUESTED:
Adopt motion as stated.
INTRODUCTION: