Western Shorewood Stormwater Management Plan Draft 1-23-20Western Shorewood
Stormwater Management Plan
Prepared for
City of Shorewood
DRAFT 1/23/2020
Western Shorewood Stormwater Management Plan
Draft 1/23/2020
Contents
1 Introduction ............................................................................................................................................. ..............................1
1.1
Project Area ......................................................................................................................................... ..............................1
1.2
Past Studies ......................................................................................................................................... ..............................1
1.2.1
Hydrologic /Hydraulic Analysis Freeman Park Feasibility Study (April 2017) ....... ..............................1
1.2.2
Freeman Park Feasibility Study Summary Memorandum (May 2018) ................... ..............................1
1.2.3
Western Shorewood Water Resources Planning — MCWD Technical Review and Regulatory
Analysis Memorandum (July 2018) ...................................................................................... ..............................1
1.2.4
HCRRA Stormwater Infrastructure Qualitative Failure Risk Analysis Memorandum (February
2018) ................................................................................................................................................ ...............................
2
1.3
Project Scope ...................................................................................................................................... ..............................2
1.4
Project Goals ....................................................................................................................................... ..............................3
2 Existing Conditions ................................................................................................................................ ..............................5
2.1
Summary of Drainage Issues ........................................................................................................ ..............................5
2.1.1
Shorewood Oaks ......................................................................................................................... ..............................5
2.1.2
Strawberry Lane ........................................................................................................................... ..............................6
2.1.3
Freeman Park ................................................................................................................................ ..............................6
2.1.4
Beverly Drive and Cajed Lane Wetlands ............................................................................. ..............................7
2.1.5
Grant Lorenz Channel ................................................................................................................ ..............................7
2.1.6
Noble Road .................................................................................................................................... ..............................9
2.2
XP -SWMM Model Updates ........................................................................................................... ..............................9
2.2.1
Design Storm Event Results ................................................................................................... .............................10
2.2.2
Potentially Impacted Structures ........................................................................................... .............................10
2.3
Water Quality Evaluation .............................................................................................................. .............................14
2.3.1
P8 Model Development ........................................................................................................... .............................14
2.3.2
Minnesota Board of Water and Soil Resources ( BWSR) .............................................. .............................14
2.3.3
Pollutant Loads & Existing Removals ................................................................................. .............................14
2.4
Other Background Information .................................................................................................. .............................19
2.4.1
Minnesota Department of Natural Resources (MnDNR) Public Waters ............... .............................19
2.4.2
United States Fish and Wildlife Service (USFWS) National Wetlands Inventory (NWI) ...............19
2.4.3
MCWD Functional Assessment of Wetlands (FAW) Inventory ................................. .............................19
P: \Mpls \23 MN \27 \23271686 Western Shorewood StormwaterM \WorkFiles\ Report\ WestemShorewoodStormwaterManagementPlan _DRAFT_012320120.docx
3 Proposed Conditions ........................................................................................................................... .............................23
3.1
Preliminary Alternatives Analysis ............................................................................................... .............................23
3.1.1
Planning Level Costs ................................................................................................................. .............................23
3.2
Preferred Alternatives Analysis ................................................................................................... .............................24
3.2.1
Shorewood Oaks ........................................................................................................................ .............................26
3.2.2
Strawberry Lane .......................................................................................................................... .............................29
3.2.3
Freeman Park ............................................................................................................................... .............................36
3.2.4
Beverly Drive and Cajed Lane Wetlands ............................................................................ .............................39
3.2.5
Grant Lorenz Channel ............................................................................................................... .............................42
3.2.6
Noble Road ................................................................................................................................... .............................49
4 Recommended Plan ............................................................................................................................. .............................52
4.1.1
Combined Evaluation ................................................................................................................ .............................52
4.1.2
Recommended Project Implementation, Cost, and Sequencing ............................. .............................57
4.1.3
Potential Funding Sources ...................................................................................................... .............................58
List of Tables
Table 2 -1 Existing Conditions XP -SWMM Model Results for Flood Elevations and Potentially- Impacted
Structures............................................................................................................................... .............................12
Table 2 -2 Grant Lorenz and Pebble Brook Creek Existing Conditions Results ............................ .............................13
Table 2 -3 Existing Conditions Summary of Annual P8 Pollutant Load Reductions ................... .............................17
Table 2 -4 Existing Conditions Summary of Annual Pollutant Loads Related to Erosion ......... .............................18
Table 3 -1 Preferred Alternatives Summary ................................................................................................ .............................25
Table 3 -2 Estimated Treatment Volumes to Meet MCWD Rules for Strawberry Lane CIP Project ...................30
Table 4 -1 Recommended Plan XP -SWMM Model Results for Flood Elevations and Potentially- Impacted
Structures............................................................................................................................. ............................... 55
Table 4 -2 Recommended Plan XP -SWMM Results along the Grant Lorenz Channel and Pebble Brook
Creek...................................................................................................................................... ............................... 56
Table 4 -3 Recommended Plan Estimated Pollutant Load Reductions .......................................... ............................... 56
Table 4 -4 Summary of Western Shorewood Stormwater Management Recommended Plan ........................... 58
Table 4 -5 Summary of Potential Grant Funding Sources ..................................................................... .............................60
List of Figures
Figure 1 -1 Western Shorewood Project Area ............................................................................................. ..............................4
Figure 2 -1 Existing Conditions along the Grant Lorenz Channel (Upstream (a) to Downstream (d) from
GrantLorenz Road) .............................................................................................................. ..............................8
Figure 2 -2 Existing Conditions Atlas 14 100 -Year, 24 -Eour Event Inundation ........................... ...............................
11
Figure 2 -3 Existing Conditions P8 Pollutant Model BMPs ................................................................. ...............................
16
Figure2 -4 MnDNR Public Waters .................................................................................................................. .............................20
Figure 2 -5 USFWS National Wetland Inventory ....................................................................................... .............................21
Figure2 -6 MCWD Wetland Inventory .......................................................................................................... .............................22
Figure 3 -1 Shorewood Oaks Preferred Alternatives (5O1, SO2) ........................................................ .............................28
Figure 3 -2 Strawberry Lane Preferred Alternative ( SL1) ........................................................................ .............................34
Figure 3 -3 Strawberry Lane Preferred Alternative ( SL2) ........................................................................ .............................35
Figure 3 -4 Freeman Park Preferred Alternative ( FP1) ............................................................................ .............................38
Figure 3 -5 Beverly Drive and Cajed Lane Preferred Alternative ( 131) ............................................... .............................41
Figure 3 -6 Grant Lorenz Preferred Alternative (GL1) ............................................................................. .............................47
Figure 3 -7 Grant Lorenz Preferred Alternative (GL2) ............................................................................. .............................48
Figure 3 -8 Noble Road Preferred Alternative ( NR1) ............................................................................... .............................51
Figure 4 -1 Western Shorewood Recommended Plan ......................................................................... ...............................
54
List of Appendices, Attachments, or Exhibits
Appendix A Western Shorewood Stormwater Management Plan: Preliminary Alternatives Review Meeting
iv
Presentation Slides (11/7/2019)
Appendix B
Western Shorewood Stormwater Management Plan:
Preferred Alternatives Review Meeting
Presentation Slides (12/18/2019)
Appendix C
Western Shorewood Stormwater Management Plan:
City Council Work Session Presentation
Slides (1/27/2020)
Appendix D
Western Shorewood Stormwater Management Plan:
Open House Boards (TBD)
Appendix E
Western Shorewood Stormwater Management Plan:
Preferred Alternatives Planning Level
Engineer's Opinion of Probable Cost
iv
Certification
I hereby certify that this engineering document was prepared by me or under my direct personal
supervision and that I am a duly licensed Professional Engineer under the laws of the State of
Minnesota.
Jennifer Koehler, PE Date
MN PE #: 47500
Abbreviations
ASTM American Society for Testing and Materials
BWSR Board of Water and Soil Resources
CFS Cubic feet per second
CIP Capital Improvement Project
CMP Corrugated Metal Pipe
FAW Functional Assessment of Wetlands
HCRRA Hennepin County Regional Railroad Authority
HSG Hydrologic Soil Group
MCWD Minnehaha Creek Watershed District
MnDNR Minnesota Department of Natural Resources
MPCA Minnesota Pollution Control Agency
MSL Mean Sea Level
NOAA National Oceanic and Atmospheric Administration
NPDES National Pollution Discharge Elimination System
NURP Nationwide Urban Runoff Program
NWI National Wetland Inventory
P8 Program for Predicting Polluting Particle Passage through Pits, Puddles, & Ponds
PVC Polyvinyl Chloride
PWI Public Waters Inventory
RCP Reinforced Concrete Pipe
SSURGO Soil Survey Geographic Database
TP Total Phosphorus
TSS Total Suspended Solids
USFWS United States Fish and Wildlife Service
Vi
I Introduction
Barr was directed by City of Shorewood staff to develop a comprehensive
stormwater management plan (Plan) for the western portion of the City of
Shorewood that has historic and ongoing drainage issues.
This Plan builds off previous drainage investigations and feasibility studies
completed for the City of Shorewood (WSB, 2017; WSB, 2018) and considers
feedback provided by the Minnehaha Creek Watershed District (MCWD,
2018) and city staff.
1.1 Project Area
The project area includes the western portion of the City of Shorewood from
Highway 7 on the south, Edgewood Road to the north, Howards Point Drive
to the west, and Seamans Drive to the east. Figure 1 -1 shows the
watersheds included in the study area along with the six areas identified to
have drainage concerns. These areas are further discussed in Chapter 2.
1.2 Past Studies
1.2.1 Hydrologic /Hydraulic Analysis Freeman Park
Feasibility Study (April 2017)
The Hydrologic /Hydraulic Analysis Freeman Park Feasibility Study was
completed by WSB and Associates. Inc. for the City of Shorewood (dated
April 5, 2017) which evaluated five drainage issues within the Freeman Park
subwatershed.
1.2.2 Freeman Park Feasibility Study Summary
Memorandum (May 2018)
The Freeman Park Feasibility Study Summary Memorandum was completed
by WSB and Associates. Inc. for the City of Shorewood (dated May 22, 2018)
and summarized the recommendations and results from the
Hydrologic /Hydraulic Analysis Freeman Park Feasibility Study.
1.2.3 Western Shorewood Water Resources Planning -
MCWD Technical Review and Regulatory
Analysis Memorandum (July 2018)
The Western Shorewood Water Resources Planning — MCWD Technical
Review and Regulatory Analysis Memorandum was completed by MCWD
staff (dated July 26, 2018) and summarized the MCWD regulatory and
CHAPTER
SUMMARY
technical analysis of the proposed series of drainage solutions for western Shorewood identified in the
Freeman Park Feasibility Study Summary Memorandum.
1.2.4 HCRRA Stormwater Infrastructure Qualitative Failure Risk Analysis
Memorandum (February 2018)
The Hennepin County Regional Railroad Authority (HCRRA) Stormwater Infrastructure Qualitative Failure
Risk Analysis was completed in 2018 along all the corridors within the HCRRA jurisdiction to evaluate the
likelihood of stormwater infrastructure failure and the possible consequences of failure and help prioritize
infrastructure maintenance and replacement efforts. The analysis used spatial data of HCRRA's
stormwater infrastructure and other parameters related to topography, hydrology, soils, other county and
public infrastructure data (roads, trails, railroads, structures, etc.), and stormwater infrastructure inspection
data. This included evaluation of all known culverts and storm sewers crossing the Lake Minnetonka LRT
Regional Trail through the City of Shorewood including the outlet located at Freeman Park.
1.3 Project Scope
The scope of the Plan is to build off of previous work, recommendations, and review comments to further
evaluate alternatives to improve drainage conditions in the six drainage areas shown in Figure 1 -1. This
scope included:
• Topographic survey of select areas including:
o Pipe inverts, materials and structure details for the outlet from Freeman Park, at
Smithtown Road (downstream of Freeman Park), at Edgewood Road, and at the outlet
from wetland south of Beverly Drive.
• Cross - sections along the Grant Lorenz Channel where private property access was
granted
• Survey not completed as part of this Plan included utility survey, tree survey, cross -
sections along Pebble Brook (access not granted), or wetland delineations. Additional
survey will need to be completed as the city progresses with the implementation of the
recommendations from the Plan.
• Updates to the existing conditions XP -SWMM model provided by WSB and evaluation of the
Atlas 14 design storms for 1, 2, 10, and 100 -year, 24 hour events that can be used for the
evaluation of drainage improvement alternatives
• Development of inundation mapping and potentially impacted structures for the Atlas 14 100-
year, 24 -hour design storm event
• Creation of an existing conditions P8 model (based on the updated XP -SWMM model) to
evaluated existing pollutant loads and removals that can be used for the evaluation of drainage
improvement alternatives
• Evaluation of drainage improvement alternatives for the six drainage areas identified by the city,
including conceptual design, impacts on flood elevations and flows and water quality
improvement (if applicable), planning level opinions of probable cost, and permitting
consideration
• Development of the Plan document
• Meetings including alternative and plan review meetings with City and MCWD staff, a City Council
work session and a public open house to review the preferred alternative, and presentation of the
final plan to the City Council
1.4 Project Goals
The intent of this Plan is to identify preferred drainage improvement options in areas of known drainage
issues that can be incorporated into the City of Shorewood's larger capital improvement project (CIP)
planning efforts. The Plan includes conceptual designs and recommendations for the preferred
alternatives, planning level engineer's opinions of probable cost, permitting considerations,
implementation phasing recommendations, and identification of potential partnerships and funding
sources.
2 Existing Conditions
The Plan investigates opportunities to improve drainage at six locations as CHAPTER
identified by the City, including:
SUMMARY
• Shorewood Oaks (Area 1)
• Strawberry Lane (Area 2)
• Freeman Park (Area 3)
• Beverly Drive and Cajed Lane Wetlands (Area 4)
• Grant Lorenz Channel (Area 5)
• Noble Road Area (Area 6)
These areas have had historic and ongoing drainage issues. The following
section summarizes the existing drainage issues and also summarizes the
results of the existing conditions hydrologic and hydraulic modeling (XP-
SWMM) and pollutant loading modeling (P8).
2.1 Summary of Drainage Issues
2.1.1 Shorewood Oaks
Approximately 50 residences along Shorewood Oaks Drive and Oak Leaf
Trail are served by a sump pump collection system that runs parallel to the
roads in the development. The sump pump collection system includes the
private foundation drains, sump pump discharge pipes from each residence,
and two 6 -inch PVC collector pipes (both solid and perforated). Ultimately
the 6 -inch collector pipes connect to a storm sewer manhole located at the
low point on Shorewood Oaks Drive and drains north via the 48 -inch storm
sewer to Freeman Park. Given the perforations in the 6 -inch PVC collector
pipes, it is possible that the sump pump collection system is also
intercepting and conveying groundwater in the area. The portion of the
sump pump collection system within the right of way is owned and operated
by the city, while the sump pump systems and connections to the larger
system are private.
The sump pump collection system discharges to the storm sewer manhole at
the invert of the manhole (962.52 ft MSL) with much of the sump collection
system below elevation 964.0 ft MSL. During larger, intense storm events,
the storm sewer surcharges above the invert of the sump system for longer
durations reducing the capacity of the system to convey water pumped by
the private sump pump systems. During these conditions, sump pumps may
not be able to keep up with pumping water collecting in the sumps and this can result in flooding of
private property.
2.1.2 Strawberry Lane
The Strawberry Lane area north of the HCRRA Lake Minnetonka LRT Regional Trail is prone to standing
water adjacent to the roadway due to the flat topography along the section of road. Strawberry Lane
currently had a rural road section with no curb and gutter and minimal storm sewer collection. There are
two existing ponds located on the west side of Strawberry Lane, on the northwest and southwest side of
the intersection of Strawberry Court and Strawberry Lane, connected by 12 -inch CMP pipe. Runoff from
this area leaves the southernmost pond via a 12 -inch CMP pipe discharging to the east. Additionally, a
perforated drain tile system was installed in the ditches parallel to the roadway in 1995 intending to help
promote drainage of water from the area. Although city staff are not aware of any structures impacted by
high water conditions, standing water in the low areas adjacent to the roadway remains an ongoing issue.
Runoff from the northern portion of Strawberry Lane that does reach the existing ponds and downstream
conveyance system eventually discharges to Pebble Brook Creek, which is drainage channel that receives
intermittent flow, located east of Strawberry Lane and north of Peach Circle. During large storm events,
runoff from the watershed collecting on the west side of Strawberry Lane overtops the existing roadway
flowing overland east to Pebble Brook Creek. This channel is located on private property and
conversations with city staff indicate that there is erosion along the drainageway. Flows from this area
ultimately reach the storm sewer crossing at Smithtown Road and then discharges to the channel that
runs parallel to Grant Lorenz Road (the Grant Lorenz channel).
2.1.3 Freeman Park
The outlet structure located in Freeman Park on the south side of the Lake Minnetonka LRT Regional Trail
results in significant and ongoing maintenance issues for Public Works staff with debris collecting and
plugging the outlet structure. Reduced capacity at the outlet impacts peak water levels in the low area of
Freeman Park during storm events, which can exacerbate conditions for the Shorewood Oaks sump pump
collection system and can also result in temporary standing water on the sport /ball fields adjacent to the
low area.
Additionally, this outlet structure and storm sewer at the Lake Minnetonka LRT Regional Trail was flagged
as critical by the HCRRA Stormwater Infrastructure Qualitative Failure Risk Assessment (Feb 2018),
indicating pipejoint separation along the 48 -inch RCP pipe downstream of the outlet structure.
Discharge from Freeman Park is currently controlled by an 18 -inch PVC pipe going into the outlet
structure, with a control elevation of approximately 959.5 ft MSL. Flows from Freeman Park ultimately
reach the storm sewer crossing at Smithtown Road and then discharges to the Grant Lorenz channel.
Because of the size of this outlet and the storage in the low area of Freeman Park, this area already
provides significant rate control of discharge to Smithtown Road and the Grant Lorenz channel.
2.1.4 Beverly Drive and Cajed Lane Wetlands
There have been ongoing drainage issues around the two wetlands located near the intersection of
Beverly Drive and Cajed Lane. One wetland is located south of Beverly Drive and the other wetland is
located northwest of the intersection.
The wetland located south of Beverly Drive is drained by the private 8 -inch tile line that drains north to
Beverly Drive, through the backyards of homes located northwest of the intersection of Beverly Drive and
Cajed Lane although the system has no official inlet in these backyards. The tile line continues north
along Cajed Lane and ultimately discharges to the large wetland south of Edgewood Road before
reaching Lake Minnetonka.
The private tile line has collapsed north of Beverly Drive, resulting in flooding of the backyards of the
adjacent homes and the southern portion of Woodside Cemetery. Prior to the tile line collapse, this low
area in was primarily landlocked, with flows only draining to the north during the 100 -year storm event.
However, with the collapsed tile line, this low area, which is nearly the same elevation as the wetland on
the south side of Beverly Drive, is currently flooded by water from the wetland south of Beverly Drive.
Additionally, a home on the wetland south of Beverly Drive is known to be at -risk of flooding with the
surveyed low opening of the home being below the estimated peak flood elevations during the 10 -year
and 100 -year events.
2.1.5 Grant Lorenz Channel
The channel along Grant Lorenz Road begins north of the Smithtown Road, flows under several driveway
culverts on the west side of Grant Lorenz Road and ending just downstream of Noble Road. The channel
is approximately 1,800 feet long and conveys runoff from the entire watershed north of Smithtown Road,
including the watersheds to Strawberry Lane and Pebble Brook area, Freeman Park, and a smaller
watershed to the east of storm sewer crossing at Smithtown Road. The total watershed area is
approximately 322 acres.
The channel between Smithtown Road and Grant Lorenz Road appears to be stable (not eroding) with the
banks being well- vegetated and the flows regularly connecting with the adjacent floodplain. However,
downstream from Grant Lorenz Road, poorly vegetated banks in combination with high flows /velocities
have resulted in ongoing erosion along banks, downcutting of the stream channel, and contributing
sediment loads to the downstream wetland. Additionally, during high flows, water levels in the channel
impact private property, historically overtopping the driveways and destroying several culverts. Figure 2 -1
shows recent photos of erosion along the Grant Lorenz channel downstream of Grant Lorenz Road taken
in April 2019.
The Grant Lorenz channel is located entirely on private property and the City of Shorewood currently does
not have a drainage and utility easement over the length of the channel.
Based on the results of the previous feasibility study, in 2018, the City of Shorewood purchased the
approximately 5 acre parcel at 26245 Smithtown Road (between Smithtown Road and the Lake
Minnetonka LRT Regional Trail) for the construction of a stormwater pond to provide both flood storage
and rate control into the Grant Lorenz channel and water quality treatment (pollutant removal) of runoff
from the contributing watersheds.
a)
c)
b)
d)
Figure 2 -1 Existing Conditions along the Grant Lorenz Channel (Upstream (a) to Downstream (d)
from Grant Lorenz Road)
2.1.6 Noble Road
Based on conversations with City staff, our understanding is that the low point on Noble Road between
Grant Lorenz Road and Edgewood Road is temporarily flooded during larger events (e.g. the 100 -year
event).
Also, the intersection of Noble Road and Grant Lorenz Road can be temporarily inundated during larger
events (e.g. the 10 -year and 100 -year events). This is likely due to a reduction in the conveyance capacity
of the Grant Lorenz channel north of Noble Road. Additionally, the as -built drawings indicated the
culverts at Noble Road are two 48 -inch equivalent arch pipes with minimal cover. The drawing also
indicates pipe inverts of 933.0 ft MSL while the MnDNR LiDAR data suggests the invert of the channel
downstream of 935.5 ft MSL, suggesting there is approximately 2.5 feet of standing water in these pipes,
also reducing their conveyance capacity.
2.2 XP -SWMM Model Updates
For this study, Barr utilized the XP -SWMM model originally developed by WSB and Associates as part of
the Hydrologic /Hydraulic Analysis Freeman Park Feasibility Study. However, model inputs were reviewed,
and the model was updated based on additional information compiled as part of this study, especially in
the areas around the key study areas. This additional information included:
• Addition of subwatersheds around the Beverly Drive wetland the large wetland south of
Edgewood Road
• Subdivision of existing subwatersheds near Shorewood Oaks Drive and the north end of Grant
Lorenz Road
• As -built data provided by City staff
• Outlet and storm sewer survey data collected by Barr at the following locations:
• Beverly Drive (surveyors unable to located outlet from wetland, assumptions about
system made based on conversation and information from City staff)
• Freeman Park
• Smithtown Road
• Noble Road
• Edgewood Road
• Cross - section survey data collected by Barr along the Grant Lorenz channel where private
property access was granted by property owners
• Cross - section data based on Minnesota Department of Natural Resources (MnDNR) 2011 LiDAR
elevation data along Pebble Brook
• Tailwater boundary condition at Lake Minnetonka Gray's Bay Dam operating elevation
I
2.2.1 Design Storm Event Results
Once updated, the XP -SWMM model was used to evaluate the National Oceanic and Atmospheric
Administration (NOAA) Atlas 14 design storm events using the nested storm distribution for the following
events:
• 1 -year, 24 -hour (2.49 inches; 100% chance of event happening in any given year)
• 2 -year, 24 -hour (2.86 inches; 50% chance of event happening in any given year)
• 10 -year, 24 -hour (4.25 inches; 10% chance of event happening in any given year)
• 100 -year, 24 -hour (7.31 inches; 1% chance of event happening in any given year)
The existing conditions peak flood elevations for the four design storm events are summarized by
subwatershed in Table 2 -1. The existing slopes, bank full depth, peak flows, peak velocities, maximum
depth, and estimated shear for the four design storm events for the modeled reaches of the Grant Lorenz
channel and Pebble Brook are summarized in Table 2 -2.
An approximate inundation map of the peak flood elevation for the Atlas 14 100 -year, 24 -hour design
storm event was developed using the XP -SWMM model results and the MnDNR 2011 LiDAR elevation
data using a level pool methodology in each modeled subwatershed. The approximate 100 -year
inundation areas are shown in Figure 2 -2.
2.2.2 Potentially Impacted Structures
To better understand potential flooding /drainage impacts, a GIS analysis was completed utilizing the
Microsoft Building Footprints (2018) GIS layer and MnDNR 2011 LiDAR topographic data to estimate the
approximate low opening on a structure (e.g. low opening assumed the lowest elevation along the
structure edge). At a planning level, this will help understand the number of structures that may be
impacted by flooding under existing conditions and also evaluate potential impacts from proposed
drainage improvements. However, we would recommend collection of actual low opening survey data for
the lowest structures around the targeted areas as the city moves forward with final design of the
recommended projects.
The number of potentially impacted structures are summarized in Table 2 -1. Structures are summarized
as:
• At -risk: the estimated 100 -year peak elevation is greater than the estimated low opening
• Within 2 -feet of Freeboard: the estimated 100 -year peak elevation is lower than but within 2 -feet
of the estimated low opening
UN
Table 2 -1 Existing Conditions XP -SWMM Model Results for Flood Elevations and Potentially- Impacted Structures
bwatershedIll
Flood Area
Area
ii
Flood Elevation
10-year
(ft.)
2-year
MLNo.
of buildings
at risk
No. of buildings
within 2-ft freeboard
A
Grant Lorenz Channel
3.4
938.1
937.7
937.4
936.8
1
B
Grant Lorenz Channel
7.2
941.5
940.1
939.0
938.6
--
--
BEV
Beverly Dr. and Ca'ed Ln. Wetlands
23.4
953.3
951.8
950.9
950.6
1
C
Grant Lorenz Channel
6.0
938.0
937.7
937.6
937.6
--
--
CAJ
Beverly Dr. and Ca'ed Ln. Wetlands
7.5
949.0
948.1
947.5
947.3
--
3
D
Grant Lorenz Channel
1.8
948.1
946.3
940.9
940.3
1
--
E
Grant Lorenz Channel
3.5
951.9
946.9
943.5
943.1
--
1
F
Grant Lorenz Channel
9.4
953.7
950.5
949.0
948.6
3
--
G
Grant Lorenz Channel
15.6
953.8
951.5
950.3
949.6
1
2
H
8.7
956.5
953.5
952.4
952.2
--
--
1
13.5
956.5
954.0
952.7
952.5
--
--
1
6.4
956.5
954.6
954.1
954.0
1
1
K
Freeman Park
63.1
969.5
966.5
963.3
962.4
--
--
L
Strawberry Lane
8.4
970.5
970.3
969.6
968.9
5
M1
Strawberry Lane
22.4
971.9
971.7
971.6
971.5
3
M2
Strawberry Lane
6.5
971.0
970.8
970.7
970.6
1
3
N
Strawberry Lane
4.9
969.1
968.3
967.0
966.8
--
O
Strawberry Lane
7.1
970.6
970.3
969.5
968.9
--
1
P
9.3
975.0
974.5
974.0
973.8
3
13
Q1
Shorewood Oaks
8.3
975.1
974.4
973.0
972.7
3
9
Q1.2
Shorewood Oaks
11.8
975.1
974.8
974.7
974.6
1
9
Q2
Shorewood Oaks
26.7
970.9
966.5
964.4
964.1
--
2
Q3
Shorewood Oaks
4.6
974.5
1 969.9
969.5
969.5
1
3
Q4
Shorewood Oaks
2.6
974.5
973.2
973.1
973.0
4
R
4.7
969.4
969.1
968.6
968.4
2
S
47.1
976.4
975.2
974.7
974.6
--
--
U1
Grant Lorenz Channel
45.4
932.9
931.4
930.6
930.4
3
3
U2
Grant Lorenz Channel
14.2
935.3
931.4
930.6
930.4
--
4
V
5.1
969.5
969.3
968.7
968.5
--
4
WET
309.4
932.4
931.3
930.6
930.3
1
3
Table 2 -2 Grant Lorenz and Pebble Brook Creek Existing Conditions Results
Grant Lorenz Channel
G (upstream)
0.9
1.7
203.2
64.9
31.1
23.7
3.8
3.9
3.9
3.9
6.5
4.2
3.0
2.3
3.7
2.4
1.7
1.3
F
0.5
1.2
231.7
87.3
40.8
30.6
2.0
1.9
1.8
1.8
7.1
3.8
2.3
2.0
2.2
1.2
0.7
0.6
E
1.1
5.4
245.4
95.2
44.2
32.9
5.4
5.4
5.0
4.6
10.8
5.7
2.4
2.0
7.6
4.0
1.7
1.4
D
1.2
4.4
250.9
95.6
45.5
33.9
4.9
4.9
4.8
4.7
10.1
8.3
2.9
2.2
7.5
6.1
2.1
1.7
B
0.1
5
264.1
96.0
46.2
34.4
5.4
3.4
2.6
2.4
4.6
3.2
2.3
2.0
0.3
0.2
0.1
0.1
A (downstream)
1.2
3.8
267.6
98.4
47.2
35.3
6.6
5.3
4.2
4.1
4.1
3.7
3.4
2.8
3.0
2.7
2.5
2.0
Pebble
Brook
Creek
Upstream
1.2
0.3
135.0
26.4
6.8
5.7
5.9
3.5
2.1
2.0
3.0
1.1
0.6
0.5
2.3
0.8
0.4
0.4
Downstream
2.0
2.2
134.3
26.4
6.8
5.7
4.5
3.3
2.1
2.0
5.8
2.5
1.7
1.5
7.1
3.1
2.1
1.9
2.3 Water Quality Evaluation
2.3.1 P8 Model Development
To evaluate existing pollutant loads and removals by the existing ponds and wetlands in the watershed, a
P8 (Program for Predicting Polluting Particle Passage through Pits, Puddles, and Ponds) water quality
model (version 3.5) was developed based on the watershed, soils, storage, and infrastructure inputs from
the existing conditions XP -SWMM model. An assumed permanent pool depth of 3 feet was used for wet
ponds (based on review of aerial photos) modeled in P8, as no permanent pool storage information
below the control elevation was included in the XP -SWMM model for the existing ponds and wetlands.
The P8 model was used to estimate watershed runoff and pollutant loads from each subwatershed,
utilizing the Nationwide Urban Runoff Program (NURP) median particle and pollutant load file (NURP50).
We used hourly precipitation and daily average temperature data from the Minneapolis -St. Paul
International Airport for continuous simulation for 18 years (2000 -2018) to estimate average annual
pollutant loads and removals in the Western Shorewood project area.
2.3.2 Minnesota Board of Water and Soil Resources (BWSR)
The P8 model is limited to evaluating pollutant loads generated by the watershed surfaces and can
estimate pollutant removals using standard stormwater management practices. However, the P8 model
cannot account for pollutant loads associated with erosion in- channel or along stream banks.
The Minnesota BWSR Pollution Reduction Estimator (September 2010) was used to estimate sediment and
total phosphorus loads from the erosion along Pebble Brook Creek and the Grant Lorenz channel.
Historic survey data of the existing channels is not available to estimate the actual rate of erosion in these
locations. As a result, for these planning level estimates, we have used our experience with other stream
bank and channel erosion studies conducted in the Twin Cities area to estimate a rate of erosion given the
dimensions of the existing channel and photos of the current conditions of the channel.
2.3.3 Pollutant Loads & Existing Removals
Using the P8 pollutant loading model, we were able to quantify the estimated average annual total
suspended solids (TSS) and total phosphorus (TP) pollutant load reductions by existing ponds and
wetlands in the existing study area watershed. We also summarized the average annual pollutant removal
efficiency (as a percentage of the pollutant load to the pond or wetland).
For Pebble Brook Creek and the Grant Lorenz channel, the BWSR tool was used to estimate the existing
annual TSS and TP loads resulting from erosion in these channels. With the reduction in peak flows and
velocities in these channels along with the implementation of stabilization measures, these estimated
numbers reflect the amount of pollutant reduction that could be achieved if improvements are made.
14
Figure 2 -3 shows the Western Shorewood project area and the ponds and wetlands that were modeled in
the existing conditions P8 model. Table 2 -3 summarizes the P8 model estimated average annual TSS and
TP pollutant removals as well as the estimated annual removal efficiencies of the ponds and wetlands,
where appropriate. Table 2 -3 summarizes estimated annual TSS and TP loads resulting from erosion in the
Pebble Brook Creek and Grant Lorenz channels.
Table 2 -3 Existing Conditions Summary of Annual P8 Pollutant Load Reductions
17
A
Grant Lorenz Channel
--
--
--
--
--
B
Grant Lorenz Channel
Wet Pond
690
72%
1.3
43%
BEV
Beverly Dr. and Cajed Ln.
Wetlands
Wet Pond
1501
87%
3.1
57/0 °
C
Grant Lorenz Channel
--
--
--
--
--
CAJ
Beverly Dr. and Cajed Ln.
Wetlands
--
--
--
--
D
Grant Lorenz Channel
--
--
--
--
--
E
Grant Lorenz Channel
--
--
--
--
--
F
Grant Lorenz Channel
--
--
--
--
--
G
Grant Lorenz Channel
--
--
--
--
--
J
--
Wet Pond
620
32%
0.5
8.7%
K
Freeman Park
Wet Pond
5842
65%
9.2
30%
L
Strawberry Lane
Wet Pond
700
78%
1.4
48%
M1
Strawberry Lane
Wet Pond
2800
92%
6.2
65%
M2
Strawberry Lane
Infil assn
n Basin
280
34%
0.4
7%
N
Strawberry Lane
Wet Pond
384
65%
0.7
30%
O
Strawberry Lane
Wet Pond
869
58%
1.9
21%
Q1
Shorewood Oaks
--
--
--
--
--
Q1.2
Shorewood Oaks
--
--
--
--
--
Q2
Shorewood Oaks
--
--
--
--
--
Q3
Shorewood Oaks
--
--
--
--
--
Q4
Shorewood Oaks
--
--
--
--
--
R--
--
--
--
--
S
--
Wet Pond
2293
92%
5.0
64%
U1
Grant Lorenz Channel
Wet Pond
10512
71%
25.1
38%
U2
Grant Lorenz Channel
--
--
--
--
--
WET
--
Wet Pond
4646
21%
4.9
5%
17
Table 2 -4 Existing Conditions Summary of Annual Pollutant Loads Related to Erosion
R3
2.4 Other Background Information
The following section outlines additional existing information for the Western Shorewood project area
that was reviewed when determining potential permitting needs and requirements for projects. Although
these inventories can help with planning, an actual wetland boundary determination will be required
during the final design and permitting process for any project.
2.4.1 Minnesota Department of Natural Resources (MnDNR) Public Waters
Public waters are all basins and watercourses that meet the criteria set forth in Minnesota Statutes,
Section 103G.005, subd. 15 that are identified on Public Water Inventory maps and lists authorized by
Minnesota Statutes, Section 103G.201. Most work done within a public waters basin or watercourse
requires a permit from the MnDNR.
Figure 2 -4 shows the MnDNR public waters within the Western Shorewood project area.
2.4.2 United States Fish and Wildlife Service (USFWS) National Wetlands
Inventory (NWI)
The USFWS is responsible for the mapping of wetlands across the country. To date, the NWI coverage
includes nearly 100 percent of the contiguous United States, including the State of Minnesota. Using
National Aerial Photography Program (NAPP) imagery (typically dated from 1978 through 1988) in
conjunction with limited field verification, the USFWS identified and delineated wetlands, produced
detailed maps on the characteristics and extent of the national wetlands and constructed a national
wetlands database as part of the NWI. The NWI for the east - central portion of Minnesota was updated
from 2010 -2013.
Figure 2 -5 shows the location of potential wetlands identified in the NWI within the Western Shorewood
project area.
2.4.3 MCWD Functional Assessment of Wetlands (FAW) Inventory
In 2001 -2003, the MCWD undertook a Functional Assessment of Wetlands (FAW) within the entire
Minnehaha Creek Watershed District. This assessment included the evaluation of the majority of wetlands
within the MCWD, including the desktop assessment and verification of the presence of a wetland, the
mapping of the approximate wetland boundaries and assessment of wetland functions.
Figure 2 -6 shows the location of potential wetlands identified in the MCWD wetland inventory within the
Western Shorewood project area.
f
3 Proposed Conditions
For proposed conditions, we built on the alternatives evaluated as part of
the previous feasibility study, feedback from MCWD on the past feasibility
study, along with input from City of Shorewood staff. As part of the current
study, proposed conditions were evaluated in two phases that are discussed
in more detail below.
3.1 Preliminary Alternatives Analysis
For the preliminary alternatives evaluation, several high -level concepts were
evaluated for each of the flood areas, using the XP -SWMM and P8 models,
as appropriate. Planning level costs were also developed for each concept.
Ultimately, the preliminary alternatives were discussed with City and MCWD
staff at a meeting on November 7, 2019 including discussion of overall
feasibility, permitting considerations, planning level costs, technical and
engineering considerations /concerns, and anticipated project impacts.
Based on the conversation and feedback at that meeting, preferred
alternatives for each flood area were selected for further analysis.
The focus of this report will be on the preferred alternatives evaluation (see
Chapter 3.2) and the recommended implementation plan (see Chapter 4.0).
However, Appendix A includes the slides presented and discussed at the
November 7, 2019 meeting.
3.1.1 Planning Level Costs
All planning level point opinions of probable cost presented in this study
were developed for the alternatives based on the high -level conceptual
design of each project. Although the point estimate is presented, there is
cost uncertainty and risk associated with this concept -level cost estimate.
The costs reported for the projects include contingencies (20 percent),
engineering and design (25 percent), and estimated easement costs (as
applicable). The costs do not include any wetland mitigation costs and
assume that the excavated soils are not contaminated.
The potential range from the point opinion of probable costs reflects the
level of uncertainty, unknowns, and risk due to the conceptual nature of the
individual project designs. Barr used industry resources for cost estimating
(ASTM E 2516 11 Standard Classification for Cost Estimate Classification
System) to provide guidance on cost uncertainty. Based on the current level
23
CHAPTER
SUMMARY
of design (planning level concept), the cost range is expected to vary by -30 percent to +50 percent from
the planning level point opinion of probable costs.
3.2 Preferred Alternatives Analysis
The preferred alternatives selected for each flood area were further developed and analyzed during this
next phase of the study. As we moved through the evaluation of the preferred alternatives, we discussed
interim results with City staff who provided further direction on the various concepts. The results of the
preferred alternatives evaluation were discussed with City and MCWD staff at a second meeting on
December 18, 2019. Appendix B includes the slides presented and discussed at the December 18, 2019
meeting.
The following sections outline the preferred alternatives for each of the areas, based on the direction
provided by City and MCWD staff. In some locations, there may be two options further discussed as the
preferred alternatives. The discussion for each alternative includes description of the preferred
alternatives, impacts of the alternative, planning level costs of the alternative, and permitting
considerations.
The summary the preferred alternatives and the planning level cost are included in Table 3 -1. However,
the recommended plan for project implementation, based on the consideration of preferred alternatives
outlined below, is summarized in Chapter 4.0 of this report. The planning level opinion of probable cost
for each of the preferred alternatives is included in Appendix E.
24
Table 3 -1 Preferred Alternatives Summary
,
Area 1: Shorewood Oaks
Alternative 5O1: Abandon sump system and daylight
individual sumps at surface
$190,000
Alternative S02: Separate sump system and drain via gravity
to north of Lake Minnetonka LRT Regional Trail
$580,000
Area 2: Strawberry Lane
Alternative SL1: Storm sewer along Strawberry Lane and
Smithtown Road to (Proposed) Smithtown Pond
$890,000
Alternative SL2: Storm sewer along Strawberry Lane and
Parcel Lines to (Proposed) Smithtown Pond
$1,010,000
Area 3: Freeman Park
Alternative FP1: Replace and lower outlet from Freeman Park
$86,000
Area 4: Beverly Drive and Cajed Wetlands
Alternative B1: Replace drainage system from Beverly Drive
and along Cajed Lane
$720,000
Area 5: Grant Lorenz Channel
Alternative GL1: Maximized Smithtown Pond with extended
detention outlet, iron enhanced sand filtration bench & Grant
Lorenz channel stabilization
$4,150,000
Alternative GL2: Tiered Smithtown Pond with extended
detention outlet, iron enhanced sand filtration bench & Grant
Lorenz channel stabilization
$3,110,000
Area 6: Noble Road
Alternative NR1: Expand downstream channel capacity
$TBD3
1- Costs include contingencies (20 percent), engineering and design (25 percent), and estimated easement costs (as applicable)
2 - Point opinion of probable cost. However, based on the current level of design (planning level design), the cost range is expected to vary
by -30 percent to +50 percent from the point opinion of cost.
3 —TBD: To be determined — based on recent conversations with the city we are performing further analysis at this location and will be
developing a cost estimate for this location
25
3.2.1 Shorewood Oaks
Through the feasibility study process, two preferred alternatives emerged as potential solutions to the
Shorewood Oaks sump pump system surcharging issue. The two options included:
• Alternative S01: Abandon sump system and daylight individual sumps at surface
• Alternative S02: Separate sump system and drain via gravity to north of Lake Minnetonka LRT
Regional Trail
Figure 3 -1 shows the preferred alternatives for the Shorewood Oaks system and the contributing
watersheds to the project area. Each alternative is further discussed in the following sections.
Alternative SO I: Abandon sump system and daylight individual sumps at surface
Alternative S01 includes the abandoning the sump pump collection system by disconnecting and capping
each of the —50 individual homes from the collection system and allowing sump pumps to discharge to
the ground surface. With this option, the location of each sump pump discharge should be able to drain
via gravity overland to the storm sewer collection system and not exacerbate any existing surface
drainage issues or impact existing infrastructure. Additionally, it is possible that the 6" perforated PVC
collection system is intercepting and conveying groundwater from the Shorewood Oaks area and the
system should remain in place to continue to facilitate this drainage.
Complete disconnection from the sump system will eliminate the potential for the surcharging of the
storm sewer system to result in flood individual residences.
The planning level engineers opinion of probable cost is $190,000. Implementation of this alternative may
be a cost covered by the private homeowners or as a shared cost between the private homeowners and
the City of Shorewood.
The anticipated permit required for this alternative would include the general plumbing
permit and inspection.Alternative S02: Separate sump system and drain via gravity to
north of Lake Minnetonka LRT Regional Trail
Alternative S02 includes the separation of the sump pump collection system from the existing storm
sewer system that discharges to Freeman Park. This would require the installation of a separate collection
manhole and directional drilling an 8 -inch pipe that will discharge north of the Lake Minnetonka LRT
Regional Trail to allow for gravity drainage. The location and elevation of proposed pipe discharge may
be impacted by the alternative selected for the proposed Smithtown Pond (see discussion in Chapter
3.2.5) and should discharge above the proposed 100 -year flood elevation of the proposed pond to
eliminate potential for surcharging of the sump pump collection system.
Separation of the sump pump collection system as outlined above will eliminate the potential for the
surcharging of the storm sewer system to result in flood individual residences.
26
The planning level engineers opinion of probable cost is $580,000. Implementation of this alternative may
be a cost covered entirely by the private homeowners or a shared cost between the private homeowners
and the City of Shorewood.
The low area of Freeman Park is mapped as a wetland in both the NWI and the MCWD wetland
inventories. Anticipated permits required for this alternative could include:
• Permits from the HCRRA for the new pipe crossing at the regional trail
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
27
��
Sm w Rd' v�y�'�..t
C '� '��a,'ym . �� +Ae� ` � ' � Fi' c � � ir.,✓ �1-�r. �- ��y + � �' # ./ a-
�
�-- Pebble Brook Creek
�^- Grant Lorenz Channel
Existing Storm Sewer
'\ Existing Stormwater
Pond
• Proposed Structure
— Proposed Storm Sewer
Subwatersheds
Contributing
Subwatersheds
Smithtown Pond Parcel
n.pin County
_tours 2011
10 Foot Contour
2 -Foot Contour
FS, .--d Oak -0\
\I !'
MaPte Ave
0 100 200 300
Feet
1 r_.,.- \ O ii �L J�-� v l I / 1 �� "w3,��T` _ /� ."►
� 1 inch -300 feet
_ Oak ke i3 T (j � �v � °
SHO.WOOD
1 �
62 dstw
% Shorewood Oaks
.' "
i
♦,
502 Separate sump system from storm system and µ`ms e ,nna d -
on F
y'
Ak `
drain to north of regional trail
Sol: Abandon
mp system and require private
property owners
to daylight s f
sump pump/ foundation dra ns at surface
�-- Pebble Brook Creek
�^- Grant Lorenz Channel
Existing Storm Sewer
'\ Existing Stormwater
Pond
• Proposed Structure
— Proposed Storm Sewer
Subwatersheds
Contributing
Subwatersheds
Smithtown Pond Parcel
n.pin County
_tours 2011
10 Foot Contour
2 -Foot Contour
FS, .--d Oak -0\
\I !'
MaPte Ave
0 100 200 300
Feet
1 r_.,.- \ O ii �L J�-� v l I / 1 �� "w3,��T` _ /� ."►
� 1 inch -300 feet
_ Oak ke i3 T (j � �v � °
SHO.WOOD
1 �
62 dstw
% Shorewood Oaks
3.2.2 Strawberry Lane
Through the feasibility study process, two preferred alternatives emerged as potential solutions for the
drainage issues along Strawberry Lane north of the Lake Minnetonka LRT Regional Trail.
The two options included:
• Alternative SL1: Storm sewer along Strawberry Lane and Smithtown Road to Proposed Smithtown
Pond
• Alternative SL2: Storm sewer along Strawberry Lane and Parcel Lines to Proposed Smithtown
Pond
Figure 3 -2 and Figure 3 -3 show the preferred alternatives SL1 and SL2, respectively, for the Strawberry
Lane and the contributing watersheds to the project area. Each alternative is further discussed in the
following sections.
The City of Shorewood has identified a larger Capital Improvement Program (CIP) project along
Strawberry Lane from Smithtown Road to W 6211 Street that will include full reconstruction of the street
(including widening the road from —22 feet to —28 feet) along with the addition of an — 10 feet wide bike
and pedestrian trail. The preferred alternative for drainage improvements will be implemented as part of
the larger CIP project.
Additionally, the preferred alternative for Strawberry Lane must be implemented concurrently with or after
the construction of the proposed Smithtown Pond (see further discussion in Chapter 3.2.5). A portion of
treatment provided by the proposed Smithtown Pond can be applied to the MCWD stormwater treatment
requirements for linear projects. For this study, we've assumed the proposed iron enhanced sand
filtration bench discussed as part of the Smithtown Pond project will be used to meet the MCWD
stormwater treatment requirements.
The following summarizes the MCWD treatment requirements for this linear project based on the current
MCWD rules for linear projects with new or reconstructed area greater than 10,000 square feet but less
than one acre, which apply to the new /increase in impervious surface:
• No net increase in the peak runoff rate for the 1 -, 10- and 100 -year design storms
• Abstraction of the first one inch of rainfall from the site's impervious surface
o MCWD rules do indicate that if infiltration not possible, a minimum of 0.5 inch of
abstraction from site's impervious surface must be achieved along with meeting the
phosphorus reduction requirement.
o MCWD only gives filtration 50% credit toward abstraction volume
• No net increase in phosphorus loading from existing conditions
• If the linear project includes the construction of a trail or sidewalk that will not exceed 12 feet in
width and will be bordered on the downgradient side(s) by a pervious buffer averaging at least
29
one -half the width of the sidewalk or trail, the trail or sidewalk impervious area will be exempt
from the required treatment area for the volume abstraction (infiltration) rule.
During final design, the city will need to determine if the trail can be designed such that it will be exempt
from MCWD stormwater treatment requirements. Review of the soil survey data for the area around
Strawberry Lane and the Smithtown Pond area suggests that the soils are primarily C/D and B/D soils
which indicate they have limited infiltration capacity and infiltration may not be possible. Soil boring data
collected during final design will confirm soil types for stormwater design.
However, to be conservative when developing the planning level costs, we assumed that infiltration will
not be possible but that the project still will abstract 1 -inch of runoff from the impervious surfaces (rather
than 0.5 inches), and filtration would be the treatment method (which only receives 50% credit toward the
abstraction volume meaning the proposed BMP should be sized to treat double the runoff volume from
the impervious surfaces (e.g. 2- inches of runoff)).
Table 3 -2 summarizes the anticipated treatment volumes (infiltration (1 -inch of runoff) and filtration (2-
inches of runoff)) for the full Strawberry Lane road reconstruction and trail project.
Table 3 -2 Estimated Treatment Volumes to Meet MCWD Rules for Strawberry Lane CIP Project
Alternative SL 7: Storm sewer along Strawberry Lane and Smithtown Road to Proposed
Smithtown Pond
To improve drainage along the portion of Strawberry Lane north of the regional trail, Alternative SL1
includes the installation of storm sewer inlets at the key low areas west of Strawberry Lane and the
installation of an 18 -inch pipe that drains north to Smithtown Road and east along Smithtown Road to
the proposed Smithtown Pond assuming maximized storage on the entire parcel (Alternative GL1). In this
scenario, except for the high flows that overtop and flow east over Strawberry Lane and the discharges
from the existing stormwater pond at the end of Peach Circle, most runoff from smaller storm events are
diverted away from Pebble Brook Creek. Because of this reduction in flows to Pebble Brook Creek, we
have assumed that further stabilization of this channel is not required.
30
Strawberry Lane
Road Reconstruction
83,270
105,980
22,710
1,893
3,785
Strawberry Lane Trail
0
37,850
37,850
3,154
6,308
Total
83,270
143,830
60,560
5,047
10,093
Alternative SL 7: Storm sewer along Strawberry Lane and Smithtown Road to Proposed
Smithtown Pond
To improve drainage along the portion of Strawberry Lane north of the regional trail, Alternative SL1
includes the installation of storm sewer inlets at the key low areas west of Strawberry Lane and the
installation of an 18 -inch pipe that drains north to Smithtown Road and east along Smithtown Road to
the proposed Smithtown Pond assuming maximized storage on the entire parcel (Alternative GL1). In this
scenario, except for the high flows that overtop and flow east over Strawberry Lane and the discharges
from the existing stormwater pond at the end of Peach Circle, most runoff from smaller storm events are
diverted away from Pebble Brook Creek. Because of this reduction in flows to Pebble Brook Creek, we
have assumed that further stabilization of this channel is not required.
30
Since recent infrastructure improvements along Smithtown Road were completed in 2015, it was assumed
that the pipe segment along Smithtown Road would be directional drilled south of all the existing utilities
in the right -of -way to the proposed Smithtown Pond to minimize disturbance of the existing
infrastructure. Given the offsets needed for directional drilling (typically 10 ft from existing utilities), the
pipe may be located outside the existing right -of -way and a drainage and utility easement may be
required for this length of pipe.
Because the existing road overtops during the 10 -year and 100 -year events, the alternative assumes that
this overflow to the east will be maintained so that there is no increase in the peak elevation of the 100 -
year, 24 -hour design storm event on the west side of Strawberry Lane. These elevations and overflows
will need to be further considered during final design of the roadway and trails of the larger CIP project.
The proposed alternative reduces the peak elevations of water stored on the west side of Strawberry Lane
during the 1 -, 2 -, and 10 -year, 24 -hour design storm events and maintains (no increase) in the 100 -year,
24 -hour design storm events. Since the flood elevations in the 100 -year design storm event are
maintained, the number of potentially impacted structures is not expected to change. Although some
water quality treatment will be required as part of the larger road reconstruction project and will be
achieved in the proposed Smithtown Pond, the addition of the drainage infrastructure along Strawberry
Lane will have minimal impact on water quality. However, by reducing discharges to the Pebble Brook
Creek channel and reducing erosion, the project will provide some water quality benefit. The TSS and TP
annual loads are estimated to be reduced by 0.04 tons per year and 0.04 pounds per year, respectively.
The planning level engineers opinion of probable cost is $890,000. This cost focuses on the primary
infrastructure required for improving drainage along the northern portion of Strawberry Lane, including
targeted inlets /structures, storm sewer including the estimated directional drilling cost and purchase of
drainage and utility easements along Smithtown Road. The costs do not reflect the larger road
reconstruction costs and does not include the addition of curb and gutter or standard catch basins for
road design for the length of Strawberry Lane or any storm sewer needed for the portion of Strawberry
Lane south of the Lake Minnetonka LRT regional trail.
The NWI identifies one of the low areas along the west side of Strawberry Lane as wetland. The proposed
road reconstruction and drainage improvement project may result in temporary (or potentially
permanent) impacts to this wetland. Anticipated permits required for this alternative may include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1.0 acres)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Stormwater Management permits for linear redevelopment project
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
31
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
Alternative SL2: Storm sewer along Strawberry Lane and Parcel Lines to Proposed
Smithtown Pond
To improve drainage along the portion of Strawberry Lane north of the regional trail, Alternative SL2
includes the installation of storm sewer inlets at the key low areas west of Strawberry Lane and the
installation of a 24 -inch pipe along Strawberry Lane that ultimately drains east between private property
parcelsto the proposed Smithtown Pond (see Figure 3 -3). The concept for Alternative SL2 can work with
both the maximized and tiered concepts for Smithtown Pond (GL1, GI-2). In this scenario, we anticipate
that the discharges from the existing stormwater pond at the end of Peach Circle will be intercepted and
conveyed by the pipe to be located along the parcel line. Because of this, except for the high flows that
overtop and flow east over Strawberry Lane, most runoff from smaller storm events are diverted away
from Pebble Brook Creek. Because of this reduction in flows to Pebble Brook Creek, we have assumed
that further stabilization of this channel is not required.
To minimize disturbance of the trees along the parcel alignment to the east, it was assumed that the pipe
segment along the parcel line would be directional drilled from Strawberry Lane to the proposed
Smithtown Pond. This system would also capture the discharge from the existing stormwater pond at
Peach Circle. Because the alignment along the parcel lines is entirely on private property, drainage and
utility easement will be required for this length of pipe.
Similar to Alternative SL1, the alternative assumes that this overflow to the east will be maintained so that
there is no increase in the peak elevation of the 100 -year, 24 -hour design storm event on the west side of
Strawberry Lane. These elevations and overflows will need to be further considered during final design of
the roadway and trails of the larger CIP project.
The proposed alternative reduces the peak elevations on the west side of Strawberry Lane during the 1 -,
2 -, and 10 -year, 24 -hour design storm events and maintains (no increase) in the 100 -year, 24 -hour design
storm events. Since the flood elevations in the 100 -year design storm event are maintained, the number
of potentially impacted structures does not change. Although some water quality treatment will be
required as part of the larger road reconstruction project and will be achieved in the proposed Smithtown
Pond, the addition of the drainage infrastructure along Strawberry Lane will have minimal impact on water
quality. However, by reducing discharges to the Pebble Brook Creek channel and reducing erosion, the
project will provide some water quality benefit. The TSS and TP annual loads are estimated to be reduced
by 0.04 tons per year and 0.04 pounds per year, respectively.
The planning level engineers opinion of probable cost is $1,010,000. This cost focuses on the primary
infrastructure required for improving drainage along the northern portion of Strawberry Lane, including
targeted inlets /structures, storm sewer including estimated directional drilling cost and purchase of
drainage and utility easements along the parcel line to Smithtown Pond. The costs do not reflect the
larger road reconstruction costs and does not include the addition of curb and gutter or standard catch
32
basins for road design for the length of Strawberry Lane or any storm sewer needed for the portion of
Strawberry Lane south of the Lake Minnetoka LRT regional trail.
The NWI identifies one of the low areas along the west side of Strawberry Lane as wetland and a small
wetland that may fall along the alignment of the directionally drilled pipe. The proposed road
reconstruction and drainage improvement project may result in temporary (or potentially permanent
impacts to this wetland. Anticipated permits required for this alternative may include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1.0 acres)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Stormwater Management permits for linear redevelopment project
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
33
Pebble Brook Creek
Existing Storm Sewer
C3 misting Stormwater
Smithtown Pond Alternative (GL1) Pond
• Proposed Structure
a � — Pro d Storm Sewer
pose
/ c r. /`3 .W+�al, r 1 Smithtown Pond
;i (Maximized)
Subwatersheds
Contributing
Subwatersheds
,s
Hennepin County
♦ / - Contours 2011
4' r+ .•6i _ — 10 Foot Contour
2 -Foot Contour
1
r
y,�_ ,,ll//�,��ttt SL1: I stall 18 st or. sewer a long Strawberry Lane _ _ .i • �
and Smithtown Road to Smithtown Pond
0 150 300
r
�(� Feet
F f \J \(Q,/ 1 inch = 300 feet
� K I
s rn oe
SHOREWOOD
cz
Strawberry Lane
c- ref_ � �
. r ,
r
dz�d ssW . v �bz d-'St%
Preferred Alternative
B� —'oElm
A �'o�
3.2.3 Freeman Park
Through the feasibility study process, one preferred alternative emerged as the solution for the drainage
issues at the outlet structure at Freeman Park, south of the Lake Minnetonka LRT Regional Trail.
The preferred alternative includes:
• Alternative FP1: Replace and lower outlet from Freeman Park
Figure 3 -4 shows the preferred alternative FP1, and the contributing watersheds to the project area. The
preferred alternative is further discussed in the following section.
Alternative FP 7: Replace and lower outlet from Freeman Park
The existing 18 -inch pipe and storage in the low area of Freeman Park already serves to reduce peak
discharges from the watershed to Smithtown Road and the downstream Grant Lorenz channel, so
increasing pipe sizes and discharge downstream is not recommended. At the same time, surcharging of
the storm sewer and high tailwater conditions at Freeman Park, have contributed to the issues related to
the Shorewood Oaks sump pump collection system, so reductions in peak flood elevations in Freeman
Park is desired.
Alternative FP1 includes removing and replacing the existing outlet structure and 48 -inch storm sewer
with a new, lowered (elevation 957.5 ft MSL, — 2 feet lower than existing) outlet structure along with a new
18 -inch pipe crossing at the regional trail. A small amount of grading will be required to lower the
elevation of the system. The design of the new outlet structure should help prevent accumulation of
debris at the outlet and provides flow capacity even with the accumulation of some debris at the outlet
structure inlet. The conceptual outlet structure as modeled for this alternative is included on Figure 3 -4;
however, during final design, the city may select a different configuration as long as it meets the hydraulic
needs and minimizes the amount of maintenance needed.
The proposed alternative reduces the peak elevations at Freeman Park during the 1 -, 2 -, and 10 -year, 24-
hour design storm events and maintains (no increase) in the 100 -year, 24 -hour design storm events. The
adjacent ball fields have minimal inundation during the 1 -, 2 -, and 10 -year storm events with the
proposed alternative. The Freeman Park outlet structure is not anticipated to have any water quality
improvement benefit.
The planning level engineers opinion of probable cost is $86,000. Because the HCRRA flagged outlet
structure and pipe crossing at the regional trail as critical and in need of replacing, implementation of this
alternative may be a shared cost between the HCRRA and the City of Shorewood.
The low area of Freeman Park is mapped as a wetland in both the NWI and the MCWD wetland
inventories. Anticipated permits required for this alternative could include:
36
• Permits from the HCRRA for the new pipe crossing at the regional trail
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Waterbody Crossing and Structures permit (if comes into contacted with bed or bank)
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
37
CONCEPTUAL OUTLET CONFIGURATION
W,,w, �` • t
E
Smithtown Pond Alternative
(GL1, GL2)
i{ ..r
FP1: Replace and lower outlet from Freeman Park to 957.5 ft MSL
1
51 , -. `-��•`��t ,:,� !"I`ficty "� .� � Ml^ �' F' +: % � -_,� I �\ \\ I� �� %S ) �C
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1
_-
.62n
,�II�� �V(`,/
ww Pebble Brook Creek
-M-- Grant Lorenz Channel
Existing Storm Sewer
Existing Stormwater
Pond
• Proposed Structure
_ Proposed Storm
Sewer
Smithtown Pond
Parcel
Subwatersheds
Contributing
Subwatersheds
Hennepin County
Contours 2011
10 -Foot Contour
2 -Foot Contour
O
0 200 400
Feet
1 inch = 400 feet
SHOREWOOD
3.2.4 Beverly Drive and Cajed Lane Wetlands
Through the feasibility study process, one preferred alternative emerged as the solution for the drainage
issues at the Beverly Drive and Cajed Lane wetlands.
The preferred alternative includes:
• Alternative 131: Replace drainage system from Beverly Drive and along Cajed Lane
Figure 3 -5 shows the preferred alternative 131, and the contributing watersheds to the project area. The
preferred alternative is further discussed in the following section.
Alternative B7: Replace drainage system from Beverly Drive and along Cajed Lane
Alternative 131 assumes that the currently collapsed 8 -inch tile system is replaced with a similarly sized (8-
inch) system from the Beverly Drive wetland along Cajed Lane to the large wetland south of Edgewood
Road. The assumption is that the existing 8 -inch system would be filled and left in place and much of the
new piping would be installed via directional drilling to reduce surface disturbance. Additionally, an inlet
will be added to the low area in the backyards northwest of the intersection of Beverly Drive and Cajed
Lane; however, the proposed inlet will need to connect to the system along Cajed Lane after the discharge
from the Beverly Drive wetland has dropped in elevation to prevent water in the wetland from flooding
the backyards (similar to the conditions with the existing collapsed pipe). This system has historically
been a private drainage system and the city will likely have to obtain drainage and utility easements over
the alignment on private property.
Several alternatives considering upsizing the drainage system (up to a 24 -inch pipe) from the Beverly
Drive wetland to the large wetland south of Edgewood Road were evaluated; however, the flood risk of
the known home on the Beverly wetland could not be eliminated even with these increased pipe sizes.
City staff indicated that there may be future opportunities on this property to reduce or eliminate the
structure flood risk through floodproofing efforts or future sale /redevelopment of the parcel.
The proposed alternative slightly reduces the peak flood elevations on the Beverly Wetlands during the 1 -,
2 -, 10 -, and 100 -year, 24 -hour design storm events. In the low area in the backyards northwest of the
intersection of Beverly Drive and Cajed Lane, the alternative reduces the peak flood elevations during the
1 -, 2 -, 10 -, and 100 -year, 24 -hour design storm events. Additionally, the estimated number of structures
within 2 -feet of freeboard is reduced by 2 in the backyards of properties northwest of Beverly Drive and
Cajed Lane. Replacing the drainage system from the Beverly Drive wetland is not anticipated to have any
water quality improvement benefit.
The planning level engineers opinion of probable cost is $720,000.
39
The wetland south of Beverly Drive is mapped by both the NWI and the MCWD wetland inventories and
the backyard area northwest of Beverly Drive and Cajed Lane is mapped as wetland in the MCWD
inventory. Anticipated permits required for this alternative could include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1 acre)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Waterbody Crossing and Structures permit (if comes into contacted with bed or bank)
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
40
,y
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4
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Existing Storm Sewer
., -
Q Cj Existing Stormwater
Pond
• Proposed Structure
.. ...
Proposed Storm
Sewer
Subwatersheds
Contributing
} l / • \ Subwatersheds
, �.{. Hennepin County
Contours 2011
10 Foot Contour
2 -Foot Contour
B7" Replace system (8) from Beverly Drive
Wetland to wetland north of Smithtow Road,
_
and add inlet and storm sewer (8') in to area , a I --
t "de of C )ed Lane
�i.fst i a.?ma. iti
IIrrk
1 I
0 100 200
v
r R Feet
1 inch = 200 feet
Beverly L� F� 5 w SHOREWOOD
Y t r
� /TI D
Wetlands
Preferred Alternative
�%
3.2.5 Grant Lorenz Channel
Through the feasibility study process, two preferred alternatives emerged as potential solutions for the
drainage issues along the Grant Lorenz channel downstream of Smithtown Road.
The two options included:
• Alternative GL1: Maximized Smithtown Pond with extended detention outlet & Grant Lorenz
channel stabilization
• Alternative GL2: Tiered Smithtown Pond with extended detention outlet & Grant Lorenz channel
stabilization
Figure 3 -6 and Figure 3 -7 shows the preferred alternatives GL1 and GL2, respectively, for the Grant Lorenz
channel and the contributing watersheds to the project area. Each alternative is further discussed in the
following sections.
Alternative GL 7: Maximized Smithtown Pond with extended detention outlet, iron
enhance sand filtration bench & Grant Lorenz channel stabilization
Alternative GL1 includes the construction of a stormwater pond (Smithtown Pond) on the parcel at 26245
Smithtown Road to provide flood storage and rate control for discharges to the Grant Lorenz channel as
well as additional water quality treatment of flows from the contributing watershed. This includes all
subwatershed located south of Smithtown Road, including runoff from the local watershed (subwatershed
1), Pebble Brook Creek (subwatershed H), Freeman Park (subwatershed K), and subwatershed J (see Figure
2 -2 for subwatershed identification).
The grading of Smithtown Pond for Alternative GL1 maximizes the footprint of storage on the parcel
providing both water quality treatment and flood storage below the existing 100 -year, 24 -hour design
storm event elevation using an extended detention outlet structure. The conceptual outlet structure of
Smithtown Pond is a notched weir with an 18 -inch wide notch at the pond's normal water level (952.0 ft
MSL) and a 6 -foot weir at an elevation of 953.0 ft MSL. The outlet structure would tie into the existing two
42 -inch RCP culverts that discharge north under Smithtown Road to the Grant Lorenz channel.
The flood pool (from the proposed NWL (952.0 ft MSL) to the existing 100 -year elevation (956.5 ft MSL))
provides 13.7 acre -feet of storage. However, given the elevations and slope of this site, to develop flood
storage requires significantly more excavation than the actual flood storage provided, which adds
significant cost to this alternative. The design of basin also needs to accommodate the proposed storm
sewer discharge from Alternative FP1.
The permanent pool volume for water quality treatment (1.5 acre -ft) assumes a pond with 3 feet of depth
below the NWL. Additional water quality treatment is provided with the construction of an iron - enhanced
sand filter (IESF) bench adjacent to the pond, where stored water above the normal water level can spill
42
into the bench and that can store 12- inches of water over the media that will be filtered before
discharging via a perforated draintile collection system connected to the pond outlet structure.
The intent of the IESF bench would be to meet the MCWD stormwater management requirements for the
City's larger Strawberry Lane road reconstruction project (see discussion in Chapter 3.2.2). This concept
assumes that the Smithtown Pond will include the largest estimated IESF bench, assuming the road
reconstruction project will need to treat all new impervious surface from the roadway reconstruction and
the addition of a trail.
Most erosion within the Grant Lorenz channel is occurring in the channel downstream of Grant Lorenz
Road. Currently, the city does not have a drainage and utility easement for this channel which is located
entirely on private property. We have assumed that all access to the project would be from the east
(Grant Lorenz Road) to minimize impacts to private property and would try to minimize tree removal
which would preserve the screening and tree canopy in this area. In addition to the reduced flows
resulting from Smithtown Pond, targeted channel stabilization will reduce further bank erosion and
incising of the channel. Given the current channel conditions and shading by the tree canopy, the
proposed stabilization measures include:
• realigning the culvert on Grant Lorenz Road,
• constructed rock riffles generally spaced as shown on Figure 3 -6 to create stepped shallow pools
to reconnect flows with the floodplain, provide for energy dissipation, and reduce velocities on
the channel banks
• targeted grading and biostabilization of banks with shade tolerant vegetation, and
• targeted hard armoring of select banks based on anticipated flow patterns.
With the maximized Smithtown Pond configuration, the peak flood elevation for the 100 -year, 24 -hour
design storm event on the south side of Smithtown Road is maintained from existing conditions. The peak
flood elevations for the 1 -, 2 -, and 10 -year, 24 -hour design storm events are reduced. Additionally, with
the extended detention outlet structure, flows to the Grant Lorenz channel are reduced significantly for all
design storm events (ranging from 21 %to 50 %, depending on the event and location). Additionally, 100 -
year flood elevations are reduced along the channel and reduce the estimated number of potentially
impacted structures by 4.
Water quality improvements for the maximized Smithtown Pond alternative include:
• The wet retention pond removes 3,409 pounds of TSS and 9.1 pounds of TP annually
• The IESF, assuming treatment of all new impervious surfaces from the Strawberry Lane road
reconstruction project, removes 382 pounds of TSS and 2.3 pounds of TP annually
• The flow reduction and targeted stabilization in the Grant Lorenz channel could reduce TSS
loading by 1.1 tons per year and TP loading by 1.1 pounds per year.
43
The planning level opinion of probable cost is $4,150,000.
Anticipated permits required for this alternative include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1 acre)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Waterbody Crossing and Structures permit (if comes into contacted with bed or bank)
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
Alternative GL2: Tiered Smithtown Pond with extended detention outlet, iron enhanced
sand filtration bench & Grant Lorenz channel stabilization
Alternative GL2 includes the construction two tiered ponds on the parcel at 26245 Smithtown Road to
provide water quality treatment, flood storage, and rate control for discharges to the Grant Lorenz
channel. The tiered design will only be able to work with Strawberry Lane Alternative SL2. The design will
help manage flows from the subwatersheds located south of Smithtown Road, including runoff from the
local watershed (subwatershed 1), Pebble Brook Creek (subwatershed H), Freeman Park (subwatershed K),
and subwatershed J (see Figure 2 -2 for subwatershed identification).
This tiered approach reduces the amount of excavation needed to provide the flood storage, rate control,
and water quality treatment volumes, given the existing slope and elevations on the parcel. The proposed
upper and lower basins are separated by an earthen berm with an embankment elevation of 963.0 ft MSL
and includes the use of two extended detention outlet structures at both the upper and lower basins.
For the upper basin, the grading creates a wet pond with a NWL of 958.0 ft MSL and is drained to the
lower basin through a 10 -inch pipe draining to the lower basin. The permanent pool volume for water
quality treatment (0.99 acre -ft) assumes a pond with 3 feet of depth below the NWL. The flood pool
(from the proposed NWL (958.0 ft MSL) to the proposed 100 -year elevation (962.8 ft MSL)) provides 6.3
acre -feet of storage. Although this conceptual design fully contains the 100 -year peak elevation for the
estimated runoff to the upper basin, the embankment could be designed to serve as an emergency
overflow to the lower basin. The final design of this upper basin also needs to accommodate the new
proposed storm sewer discharge from Alternative SL2.
For the lower basin, the grading creates a wet pond with a NWL of 952.0 ft MSL. The conceptual outlet
structure for the lower basin of Smithtown Pond is a notched weir with a 12 -inch wide notch at the pond's
normal water level of 952.0 ft MSL, and a 7 -foot span at an elevation of 952.5 ft MSL. The outlet structure
would tie into the existing two 42 -inch RCP culverts that discharge north under Smithtown Road to the
Grant Lorenz channel. The permanent pool volume for water quality treatment (0.94 acre -ft) assumes a
44
pond with 3 feet of depth below the NWL. The flood pool (from the proposed NWL (952.0 ft MSL) to the
existing 100 -year elevation (956.5 MSL)) provides 7.7 acre -feet of storage. The final design of this lower
basin also needs to accommodate the proposed storm sewer discharge from Alternative FP1.
The lower basin also includes additional water quality treatment is provided with the construction of an
iron - enhanced sand filter (IESF) bench adjacent to the pond and this feature will be sized similarly as
outlined in Alternative GL1. Additionally, the proposed stabilization in the Grant Lorenz channel will be
the same as outlined in Alternative GL1.
With the tiered Smithtown Pond configuration, the peak flood elevation for the 100 -year, 24 -hour design
storm event in the upper basin is 962.8 ft MSL. In the lower basin, the peak flood elevation for the 100 -
year, 24 -hour design storm event on the south side of Smithtown Road is maintained from existing
conditions. The peak flood elevations for the 1 -, 2 -, and 10 -year, 24 -hour design storm events are
reduced. Additionally, with the tiered basin and extended detention, flows to the Grant Lorenz channel are
reduced significantly for all design storm events (from 20% to 36 %, depending on the event and location
within the channel). Additionally, 100 -year flood elevations are reduced along the channel and reduce the
estimated number of potentially impacted structures by 4.
Water quality improvements for the tiered Smithtown Pond alternative include:
• The wet retention pond of the upper basin removes 403 pounds of TSS and 1.4 pounds of TP
annually
• The wet retention pond of the lower basin removes 3,068 pounds of TSS and 7.8 pounds of TP
annually
• The IESF, assuming treatment of all new impervious surfaces from the Strawberry Lane road
reconstruction project, removes 454 pounds of TSS and 2.6 pounds of TP annually
• The flow reduction and targeted stabilization in the Grant Lorenz channel could reduce TSS
loading by 1.1 tons per year and TP loading by 1.1 pounds per year.
The planning level opinion of probable cost is $3,110,000.
The MCWD wetland inventory indicates a small wetland located south of Smithtown Road. Additionally,
both the NWI and the MCWD wetland inventory indicate there are several wetlands along the Grant
Lorenz channel. Anticipated permits required for this alternative include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1 acre)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Waterbody Crossing and Structures permit (if comes into contacted with bed or bank)
• MCWD Wetland Protection permit
45
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
46
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Noble Rd
An
ii
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and channel stabilization with constructed rock riffles,
targeted hard armoring, and grading with vegetation establishment
i
e
N �GL1: Maximize Smithtown Pond storage with extended detention
f \ outlet and iron - enhanced sand filtration bench (IESF)
`I 11I{
,
,1111F
Strawberry Lane Alternative (S 1) j Iron- enhanced sand filter bench
Strawberry Ct
- i
i
y � \
Pebble Brook Creek Constructed Rock Riffles Hennepin County Contours 2011
^�— Grant Lorenz Channel _ Other Targeted Channel Stabilization 10 -Foot Contour O Grant Lorenz
Channel
Existing Storm Sewer Subwatersheds 2 -Foot Contour N Preferred
K Existing Stormwater Pond Contributing Subwatersheds
0 100 200 Alternative
- • Proposed Structure 0
CTTY OP
— Proposed Storm Sewer SHOREWOOD Feet
E3R Smithtown Pond (Maximized) 0 1 inch = 200 feet FIGURE 3-6
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GL2: Realign culvert on Grant Lorenz Road,
and channel stabilization with constructed rock riffles,
targeted hard armoring, and grading with vegetation establishment
i
GL2: Tiered Smithtown Pond storage with extended detention
outlet and iron - enhanced sand filtration bench (IESF)
/' j % , - Iron - enhanced sand filter bench
.
U Strawberry Lane Alternative (SL2) r �1
i _ I l • �� r L \
%
! /
3
tra bV
rry (a
+n... Pebble Brook Creek
A Constructed Rock Riffles
Hennepin County Contours 2011
^ti•^- Grant Lorenz Channel
_ Other Targeted Channel Stabilization
- 10 -Foot Contour
Grant Lorenz
Existing Storm Sewer
Subwatersheds
2 -Foot Contour
N Channel
O
KExisting Stormwater Pond
Contributing Subwatersheds
Preferred
0 100 200 Alternative
• Proposed Structure
0
- Proposed Storm Sewer
CT YOP
SHOREWOOD
0
Feet
BARR
Smithtown Pond (Tiered)
1 inch = 200 feet FIGURE 3-7
3.2.6 Noble Road
Through the feasibility study process, options were evaluated for the two areas along Noble Road.
For the crossing at the low point on Noble Road, two preliminary alternatives were evaluated, including
raising the road and raising the road and replacing the culvert crossings. However, the discussion with
City staff in November indicated that the temporary flooding at this low point did not warrant the
estimated cost of the proposed alternatives at this time and no further analysis was performed for this
location.
Given the limited road width and right of way along Grant Lorenz Road, there may be limited opportunity
to raise grade at the intersection Noble Road and Grant Lorenz Road enough to eliminate the temporary
inundation that occurs at the intersection. However, there is an opportunity to expand capacity of the
conveyance system and reduce the frequency that the road becomes inundated, as outlined in the
following preferred alternative:
• Alternative NR1: Expand downstream channel capacity
Figure 3 -8 shows the preferred alternatives NR1 for the Noble Road site and the contributing watersheds
to the project area. The alternative is further discussed in the following section.
Alternative NR 1: Expand downstream channel capacity
Review of the MnDNR LiDAR data indicates that the Grant Lorenz channel bankfull flow area decreases
moving downstream (north) from Noble Road, suggesting the channel limits discharge from this area. To
alleviate this condition, the cross - sectional area of the channel north of Noble Road could be expanded
before it discharges into the wetland to the north. Alternative NR1 includes the expansion the channel
conveyance capacity north of Noble Road. Currently, the city does not have a drainage and utility
easement for this channel which is located entirely on private property.
Expanding the channel capacity will include lowering the channel invert to better match the inverts of the
existing culverts and reduce the amount of standing water in the pipes. Additionally, the flow area of the
channel should be expanded to match the conveyance capacity of the two existing culverts (22.8 SF of
flow area). Based on the MnDNR LiDAR data, this means potentially doubling the bankfull conveyance
capacity of the channel north of Noble Road.
With the implementation of Smithtown Pond, peak flows and peak elevations are reduced in the Grant
Lorenz channel, which will help reduce the depth of inundation at the intersection of Noble Road and
Grant Lorenz Road. With the expansion of the channel conveyance capacity, the overtopping of the
intersection should be further reduced. No water quality improvements are anticipated with the proposed
channel expansion.
49
The planning level opinion of probable cost is $TBD and the project would likely be implemented at the
same time as the channel stabilization identified in Alternatives GL1 and GL2.
Both the NWI and the MCWD wetland inventory indicate there are several wetlands along the Grant
Lorenz channel. Anticipated permits required for this alternative include:
• Minnesota Pollution Control Agency (MPCA) National Pollution Discharge Elimination System
(NPDES) Construction Stormwater Permit (if disturbance greater than 1 acre)
• MCWD Erosion Control permit (if disturbance greater than 5,000 SF)
• MCWD Waterbody Crossing and Structures permit (if comes into contacted with bed or bank)
• MCWD Wetland Protection permit
o Wetland Conservation Act (WCA) (depending on impacts to wetland; may only be
temporary impacts)
• USACOE permit (depending on impacts to wetland area; may only be temporary impacts)
50
l 4 94
r
NR1: Increase downstream channel capacity north of Noble Road
/9q0 N bl Rd
rl
p
- BARR
A_
q_
— Increase channel
capacity
gf- Constructed Rock
Riffles
t
•.fF' Recommended
1 s Structures
S r
V_ Recommended Storm
Sewer
Other Targeted
Channel Stabilization
J 1 `� ~ y� - -^-•- Grant Lorenz
• Proposed
£'
�•.. Subwatersheds
1
k"Ki x Hennepin County
7"^ Contours 2011
10 -Foot
l \ 2 -Foot
( / }�� \��`•�� Existing Storm
Pond
Stormwater
\ Pond
Oontnb
960 a o'. Subwatersh ersheds
S fY O
0 100
3p Feet
1 inch= 118 feet
'� CTTYOP
\� ,�, - OREWOOD
4 Recommended Plan
After evaluating the preferred alternatives outlined in Chapter 3.2 and
receiving feedback from City and MCWD staff, the following sections outline
a final recommended plan for stormwater management and drainage
improvements in the Western Shorewood project area. The recommended
plan includes a combination of several preferred alternatives to help address
the various drainage issues in the different flood areas.
4.1.1 Combined Evaluation
We recommend the following preferred alternatives for implementation to
improve drainage and water quality in the identified problem areas:
• Alternative S02: Abandon sump system and daylight individual
sumps at surface
• Alternative SL2: Storm sewer along Strawberry Lane and Parcel Lines
to Proposed Smithtown Pond
• Alternative FP1: Replace and lower outlet from Freeman Park
• Alternative B1: Replace drainage system from Beverly Drive and
along Cajed Lane
• Alternative GI-2: Tiered Smithtown Pond with extended detention
outlet, iron enhanced sand filtration bench & Grant Lorenz channel
stabilization
• Alternative NR1: Expand downstream channel capacity
The recommended plan including the conceptual proposed infrastructure for
each of the recommended projects is shown in Figure 4 -2. A combined XP-
SWMM model run was completed that reflects full implementation of the
recommended plan. The results, including peak flood elevations and the
number of potentially impacted structures in the subwatersheds, are
summarized in Table 4 -1, which also summarizes the change from existing
conditions. Table 4 -2 summarizes the impacts to the flows in Pebble Brook
Creek and the Grant Lorenz channel.
Overall, the recommended plan improves drainage, reduces peak flood
elevations for smaller storm events, and either reduces or maintains peak
flood elevations for larger storm events (e.g. 100 - year).
52
CHAPTER
SUMMARY
Additionally, the recommended alternatives provide opportunities for water quality improvements in
several flood areas, including an iron - enhanced sand filtration for treatment of runoff from Strawberry
Lane, retention basins in Smithtown Pond, reduction in flows to Pebble Brook Creek, and reductions in
flow to and stabilization of the Grant Lorenz channel. The anticipated pollutant load reductions from the
implementation of the recommended plan are summarized in Table 4 -3.
53
Table 4 -1 Recommended Plan XP -SWMM Model Results for Flood Elevations and Potentially- Impacted Structures
Subwaters
_�___�
2 -��r
No. of
buildings at
risk
No. of buildings
within 2 -ft
freeboard
Change in at
risk buildings
Change in
buildings within
2 -ft freeboard
o
'SUbwatersheds H and 1 were merged with subwatershed I in the proposed condi5ons modeling for Smifimwn Pond
Table 4 -2 Recommended Plan XP -SWMM Results along the Grant Lorenz Channel and Pebble Brook Creek
Table 4 -3 Recommended Plan Estimated Pollutant Load Reductions
Average Annual T55
Removal (lbs /yr)
Average Annual T55
&moval Efficiency
Average An
T
P(lbs /yr)
rage Annual TP
Removal Efficiency ( %)
Smithtemn Pond -Tiered
®
®
®®
Lovaer Basin
or Pond TereL
®
®
®®
rr
rr•.
®
rr
rr•.
r r-
rPebble
®��
Table 4 -3 Recommended Plan Estimated Pollutant Load Reductions
Average Annual T55
Removal (lbs /yr)
Average Annual T55
&moval Efficiency
Average An
T
P(lbs /yr)
rage Annual TP
Removal Efficiency ( %)
Smithtemn Pond -Tiered
®
®
®®
Lovaer Basin
or Pond TereL
®
®
®®
rr
rr•.
®
rr
rr•.
r r-
4.1.2 Recommended Project Implementation, Cost, and Sequencing
Table 4 -4 summarizes the recommended projects for each location within the study area along with the
planning level point opinion of probable cost, anticipated project sequencing, and other implementation
considerations.
Ultimately these projects will be incorporated into the larger city CIP and exact dates will be determined
through that planning process.
57
Table 4 -4 Summary of Western Shorewood Stormwater Management Recommended Plan
Project Planning Levelw Project
ment;J
Opinion
Probable
Area 1: Shorewood Oaks
Alternative S01: Abandon sump
$190,000
Independent of
system and daylight individual
other projects
sumps at surface
Area 2: Strawberry Lane
Alternative SL2: Storm sewer along
$1,010,000
Constructed
Strawberry Lane and Parcel Lines to
concurrently with or
Proposed Smithtown Pond
after Smithtown
Pond
Area 3: Freeman Park
Alternative FP1: Replace and lower
$86,000
Constructed after
outlet from Freeman Park
Smithtown Pond
completion
Area 4: Beverly Drive and Cajed Wetlands
Alternative B1: Replace drainage
$720,000
Independent of
system from Beverly Drive and
other projects
along Cajed Lane
Area 5: Grant Lorenz Channel
Alternative GL2: Tiered Smithtown
$3,110,000
Stabilization
Smithtown Pond
Pond with extended detention
constructed
design should
outlet, iron enhanced sand filtration
concurrently with or
consider future
bench & Grant Lorenz channel
after Smithtown
discharges from SL2
stabilization
Pond
and FP1
Area 6: Noble Road
Alternative NR1: Expand
$TBD3
Constructed with
downstream channel capacity
channel
stabilization (GL2)
Total Project Implementation
$5,116,000
Cost
1 - Costs include contingencies (20 percent), engineering and design (25 percent), and estimated easement costs (as applicable)
2 - Point opinion of probable cost. However, based on the current level of design (planning level design), the cost range is
expected to vary by -30 percent to +50 percent from the point opinion of cost.
3 —TBD: To be determined — based on recent conversations with the city we are performing further analysis at this location and will be
developing a cost estimate for this location
4.1.3 Potential Funding Sources
The primary funding sources for the implementation of the recommended alternatives of the Western
Shorewood Stormwater Management Plan will be the City of Shorewood utility fund and bond proceeds.
Several of these projects have already been incorporated into the City's CIP. For some projects, there are
58
potential partnerships that may provide cost -share opportunities or special assessments that could help
fund project implementation. These include:
• Partnership with the HCRRA to cost -share the implementation of FP1 (Freeman Park outlet)
• Opportunity for cost -share or special assessment for implementation of S01 (Shorewood Oaks
sump system abandonment)
Additionally, there are a variety of grant programs that the City could apply for to assist in funding some
of these projects. These programs are offered by several entities and for varying types of projects. The
potential grant opportunities are summarized in Table 4 -5. MCWD has offered assistance to the city in
pursuing some of these grant funds given the comprehensive planning approach the city has taken to
alleviate some of the stormwater management and drainage issues in Western Shorewood.
59
Table 4 -5 Summary of Potential Grant Funding Sources
Grant Program
Sponsor
Agen_
Typical Projects Funded
Level of Funding
Assistance
Typical Application
Deadlines
Clean Water Fund
Or
State of
Competitive CWF grant for projects and practices that will
Varies — 25% local
Applications typically
Programs - Projects
MN /BWSR
protect or restore water quality in lakes, rivers or streams, or
match required
due mid to late summer
and Practices Grant
will protect groundwater or drinking water.
with grant projects
selected by end of year
Natural Resources
Hennepin
Implementation of larger projects that improve water quality
Up to $100,000 per
Applications are
Grant —
County
or preserve, establish or restore natural areas. Ideal for
project (typical
accepted all year. Funds
Opportunity Grant
projects documented as part of management plans.
projects range from
are limited and awarded
$25,000 to $50,000).
on a first -come, first -
No match required
serve basis
Conservation
MnDNR
Restoration or enhancement of prairies, wetlands, forests, or
$5,000- $400,000
Multiple deadlines per
Partners Grant
habitat for fish, game or wildlife in Minnesota
10% non -state match
year (typically one per
Program
requirement; project
quarter)
cost cap of $575,000
Five Star & Urban
National Fish
Projects aiming to improve water quality, watersheds, and
Awards range from
Applications typically
Waters Restoration
and Wildlife
species and habitats they support including restoration efforts,
$20,000 to $50,000
due in January each year
Program
Foundation
stormwater management, and water quality monitoring along
Required 1:1 match
with targeted community outreach, education and
stewardship
Local Trail
MnDNR
Program to promote relatively short trail connections between
Grants range from
Applications are typically
Connections Grant
where people live and desirable locations — improving
$5,000 to $150,000
due in the spring
significant connectivity
Required match of
25%
60
Appendix A
Western Shorewood Stormwater Management Plan: Preliminary
Alternatives Review Meeting Presentation Slides
1/7/2019
Appendix B
Western Shorewood Stormwater Management Plan: Preferred
Alternatives Review Meeting Presentation Slides
12/18/2019
Appendix C
Western Shorewood Stormwater Management Plan: City Council
Work Session Presentation Slides
1/27/2020
Appendix D
Western Shorewood Stormwater Management Plan: Open House
Boards
TBD
Appendix E
Western Shorewood Stormwater Management Plan: Preferred
Alternatives Planning Level Engineer's Opinion of Probable Cost