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DRAFT ALTERNATIVES ANALYSIS
POND LILY DAM REMOVAL
WEST RIVER
NEW HAVEN, CONNECTICUT
July 2011
MMI #1899-08
Prepared for:
Town of Woodbridge
11 Meetinghouse Lane
Woodbridge, Connecticut 06525
Prepared by:
MILONE &MACBROOM,INC.99 Realty Drive
Cheshire, CT 06410
(203) 271-1773www.miloneandmacbroom.com
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POND LILY DAM ALTERNATIVES ANALYSIS
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TABLE OF CONTENTS
1.0 INTRODUCTION
1.1 Project Background .............................................................................................. 1-11.2 Project Goals and Objectives ............................................................................... 1-11.3 Previous Studies ................................................................................................... 1-3
1.4 Current Phase of Work Scope .............................................................................. 1-4
2.0 EXISTING ENVIRONMENT2.1 The West River An Overview ........................................................................... 2-1
2.2 Pond Lily Dam ..................................................................................................... 2-6
2.3 Preliminary Wetland Assessment ...................................................................... 2-102.4 Wildlife Assessment and Fishery Resources ..................................................... 2-19
2.5 West River Downstream of Pond Lily Dam ...................................................... 2-20
2.6 Sensitive Species Review .................................................................................. 2-232.7 Sensitive Historical/Archeological Resources ................................................... 2-23
3.0 SEDIMENT ANALYSIS
3.1 Overview .............................................................................................................. 3-13.2 Summary of 2011 Sediment Probing ................................................................... 3-1
3.3 Sampling Locations & Methodology ................................................................... 3-5
4.0 HYDROLOGY
4.1 Hydrologic Analysis ............................................................................................ 4-14.2 Flood Flows ......................................................................................................... 4-1
4.3 Low Flows ........................................................................................................... 4-3
5.0 HYDRAULIC ANALYSIS
5.1 Overview .............................................................................................................. 5-1
5.2 Model Results ...................................................................................................... 5-1
6.0 ALTERNATIVES ANALYSIS
6.1 Overview .............................................................................................................. 6-1
6.2 Target Fish Species .............................................................................................. 6-16.3 No Action Alternative .......................................................................................... 6-4
6.4 Alternative #1 Full Spillway Removal ............................................................. 6-4
6.5 Alternative #2 Partial Spillway Removal with Channel Alignment #1 ............ 6-56.6 Alternative #3 Partial Spillway Removal with Channel Alignment #2 ............ 6-7
6.7 Alternative #4 Partial Spillway Removal with Channel Alignment #3 ............ 6-7
6.8 Sediment Management Alternatives .................................................................. 6-106.9 Engineering and Ecological Considerations ...................................................... 6-10
6.10 Comparison of Alternatives ............................................................................... 6-13
6.11 Likely Permitting Requirements ........................................................................ 6-14
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POND LILY DAM ALTERNATIVES ANALYSIS
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LIST OF TABLES
Table 2-1 Land Use in the West River Watershed ............................................................... 2-1
Table 2-2 Palustrine Open Water ....................................................................................... 2-11Table 2-3 Palustrine Emergent Marsh ................................................................................ 2-13Table 2-4 Palustrine Scrub Shrub ....................................................................................... 2-14
Table 2-5 Palustrine Forested ............................................................................................. 2-15
Table 2-6 Upland Forested ................................................................................................. 2-16
Table 2-7 Upland Shrub/Meadow ...................................................................................... 2-17Table 2-8 Pond Lily and Associated Wetland Functions and Values Assessment ............ 2-18
Table 2-9 Wildlife Inventory .............................................................................................. 2-19
Table 3-1 Estimated Sediment Volume ................................................................................ 3-2
Table 3-2 Undrained In-Situ Sediment Shear Strengths ...................................................... 3-5
Table 4-1 West River Flood Discharges .............................................................................. 4-2
Table 4-2 West River Peak Annual Floods .......................................................................... 4-2
Table 4-3 Seasonal Flows from StreamStats Analysis ......................................................... 4-3
Table 5-1 Hydraulic Models Provided by FEMA ................................................................ 5-2
Table 5-2 Preliminary Hydraulic Modeling Results Water Surface Elevation ................. 5-3
Table 6-1 Fish Passage Requirements for Target Species ................................................... 6-2
Table 6-2 Comparison of Alternatives ............................................................................... 6-13
LIST OF FIGURES
Figure 1-1 Location Plan ....................................................................................................... 1-2
Figure 2-1 Watershed Map .................................................................................................... 2-2
Figure 2-2 Impoundments within the Watershed .................................................................. 2-4
Figure 2-3 Bridge Locations Along the West River .............................................................. 2-5
Figure 2-4 Wetland Vegetation Cover ................................................................................. 2-12
Figure 3-1 Sediment Types .................................................................................................... 3-3
Figure 3-2 Sediment Depths .................................................................................................. 3-4
Figure 6-1 Alternative #2....................................................................................................... 6-6
Figure 6-2 Alternative #3....................................................................................................... 6-8Figure 6-3 Alternative #4....................................................................................................... 6-9
Figure 6-4 Illustrative Plan .................................................................................................. 6-15
Figure 6-5 Illustrative Section ............................................................................................. 6-16
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LIST OF APPENDICES
Appendix A List of ResourcesAppendix B Soil Survey Mapping
Appendix C Natural Diversity Data Base CorrespondenceAppendix D Cultural & Archeological Resource Correspondence
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EXECUTIVE SUMMARY
Project Background
Milone & MacBroom, Inc. was retained by the Town of Woodbridge to analyze designalternatives and evaluate the ecological impacts and benefits associated with full or partialremoval of the Pond Lily Dam. The Pond Lily impoundment covers almost four acres of open
water and wetlands, but much of it has filled with sediment and now supports an emergent wet
marsh. The dam consists of an earthen berm and a 191-foot long, six-foot high spillway over
which water is conveyed to the downstream reaches of West River. The dam is physicallylocated in the City of New Haven near its boundary with the Town of Woodbridge (the
impoundment extends into the Town of Woodbridge). The dam and surrounding land are owned
by the New Haven Land Trust.
The Town of Woodbury in collaboration with the New Haven Land Trust, American Rivers, the
Connecticut Department of Energy and Environmental Protection (DEEP), and the City of NewHaven are pursuing restoration of West River, improved fish passage, and ecological function of
the area near the Pond Lily Dam through partial or full dam removal. Other critically important
factors of interest are site aesthetics, public access, and education.
Project Goals & Objectives
The following goals and objectives have been identified for the removal of Pond Lily Dam andrestoration of the West River in the area of the impoundment. These have been formulated in
conjunction with local, state, and federal project partners and serve as a benchmark measure forthe effectiveness of each of the alternatives evaluated at this site. They are as follows:
1. Restore the river habitat to a more natural environment.2. Enable passage of target fish species, including alewife, blueback herring, and American eel.3. Provide flood relief for residents of Woodbridge Flats with additional flood storage created
with the removal of Pond Lily Dam.4. Mitigate liability associated with failure of Pond Lily Dam via breaching or removal.5. Maintain or enhance habitat in the project area.6. Promote recreational use Pond Lily Nature Preserve.The Pond Lily Dam is in poor shape and in danger of failing. A full or partial breach of the
concrete spillway would eliminate the liability associated with the structure. Though it is not
critical that the entire spillway be removed, a breach must be large enough to create asustainable, fish passable channel with enough hydraulic capacity such that the remaining
structure does not impound water or function as a dam under any flow condition.
The Pond Lily impoundment supports a wetland fringe, with a more significant vegetated scrub
shrub wetland community on the eastern edge. This is not an unusual type of wetland
community in Connecticut, as this type of habitat is abundant in many impounded river systems.
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However, it is recognized that water surface elevations, river hydraulics, and the existing wetlandhabitat will be affected by dam removal and creation of a thriving ecological community
following dam breach is a key project goal.
Work Completed to Date
Milone & MacBroom, Inc. was retained in late March 2011. To date, existing data has beengathered and reviewed; field survey and base mapping has been completed; assessment of the
spillway and dam has been undertaken; ecological communities have been evaluated through
field studies; sediment probing and physical characterization has been completed; hydrologic and
hydraulic analysis has been performed; dam removal alternatives have been evaluated; and twomeetings have been held with the Advisory Committee. Sediment quality sampling and analysis
is pending review of and concurrence with the proposed sediment sampling plan by DEEP.
Alternatives Analysis
An alternatives analysis was undertaken for the Pond Lily Dam that evaluated a no actionalternative and four action alternatives as follows:
Alternative #1 Full Spillway Removal
Alternative #2 Partial Spillway Removal With Channel Alignment #1Alternative #3 Partial Spillway Removal With Channel Alignment #2
Alternative #4 Partial Spillway Removal With Channel Alignment #3
Under Alternative #1, the full 191-foot spillway would be removed. Under Alternatives #2
through 4, only a portion of the spillway would be removed, sufficient to create a viable channel.Within these alternatives, various channel alignments were evaluated.
Partial width, full depth spillway removal meets the identified project goals and objectives forWest River without the added cost of removing the entire stone and concrete structure. Partial
spillway removal would restore the river back to a more natural condition, improve upstream
water quality, enhance habitat, and allow passage of target fish species. Upon partial removal ofthe spillway, there would be no need for long-term operations and maintenance of the structure,
thus creating a sustainable channel condition. For these reasons, partial spillway removal is
recommended.
Engineering & Ecological Considerations
Regardless of the final channel alignment and sediment management strategy agreed upon forthe restoration of West River, the partial width, full depth spillway removal proposed in
Alternatives #2, #3, and #4 will need to incorporate stabilization of the berm along Whalley
Avenue as well as the remaining spillway. The design must address filling and grading in amanner to both support natural channel design as well as the ecological, aesthetic and
recreational value of the created channel but also to protect the remaining structures and adjacent
shopping center (Walgreens) parking lot. Hydraulic analysis indicates that a breach of
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POND LILY DAM ALTERNATIVES ANALYSIS
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approximately 100 feet will achieve fish passage and channel restoration but will not impoundwater under high flow conditions such that the remaining area would no longer act as a dam.
Other considerations are enumerated below.
Natural Channel Design The goal of the human, wetland, and aquatic habitat at the Pond Lily
preserve post-dam removal is to improve upon and enhance the current ecological value of thesite. Natural habitat design must take into consideration channel width, slope, shape, andphysical features such as woody debris, substrate, bank construction materials, and hydraulic
features. Hydrologic analysis and hydraulic modeling indicate that the water depths under very
low summertime conditions following spillway breach will be quite shallow (on the order of four
or five inches), similar to downstream conditions. During typical springtime fish migrationconditions, water depth will be sufficient to pass fish (on the order of seven to eight inches).
Instream habitat features can also be incorporated into the design to cause localized backwater
and scour pools to provide greater depth and habitat diversity. The West River has a very flatslope through the project area and consequently will have low velocities under a wide range of
flows. Even under extreme high flow events, velocities are predicted in the 3.0 to 5.0 feet per
second (fps) range. During the spring fish migration season, velocities of around 2.0 fps arepredicted.
Wetland Habitat Under current conditions, the ground elevation in the existing marsh area is
slightly higher than the water surface elevation. Under a full depth breach condition, normalwater surface elevations are predicted to be five to six feet lower. As such, the existing scrub
shrub wetland will be significantly higher in elevation as compared to the adjacent water. There
will be opportunity to create new wetland on either side of the newly created channel; however,the extent and type will depend upon the amount of excavation that is undertaken. Three
wetland types are possible: (1) palustrine emergent marsh, which would support emergent wetmeadow plant species; (2) palustrine scrub shrub wetland; and (3) palustrine forested wetland,
which would support a more woody vegetation. At higher elevations, an upland forested riparian
buffer is possible. The emergent marsh habitat would require the greatest degree of sedimentexcavation, followed by scrub shrub habitat, forested wetland, and finally forested upland.
Removal of other Possible Fish Passage Barriers During the field assessment and investigationassociated with the planning for the Pond Lily Dam removal, MMI staff noted three potential
barriers to fish passage in this section of the West River, in addition to the Pond Lily Dam.
Although the majority of the original spillway impounding Konolds Pond upstream of Pond
Lily has been removed, the base of the concrete spillway remains in place, creating a potentialfish passage barrier during low flow periods. In addition, two boulder weir structures were
observed across the channel at 300 feet and 500 feet downstream of the Pond Lily Dam, which
could be barriers to fish passage during low flow periods. Although detailed design of removalof these structures is not included in the current scope of work, these are addressed in a
conceptual level, with a recommendation that these barriers be removed to allow complete
restoration of fish passage to this section of the West River.
Recreational Opportunities Future raised boardwalk trails and educational features are possible
in the post-removal conditions at Pond Lily, with pedestrian access from either or both the
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eastern bank off South Genesee Street and/or from the west via constructed pedestrian bridge.These project elements will be refined with important input from the New Haven Land Trust as
the project proceeds.
Preliminary Recommendations
Based on the analysis conducted to date, the following actions are recommended:
1. Remove approximately half (100 feet) of the masonry spillway at Pond Lily Dam. This,along with channel restoration, will enable fish passage, provide structural stability along the
adjacent banks, and will not create a condition where the remaining structure will impoundwater under high flows.
2. Partially excavate sediment within the impoundment to create a new channel. TheAlternative #4 alignment will result in the most natural channel design and minimize
sediment excavation. This alignment is also believed to be the historic channel alignment
prior to dam construction. A construction access haul road could be partially left in place tomaintain the west bank of the newly formed channel, and to shelter both Whalley Avenue
and the adjacent commercial plaza.
3. Incorporate natural habitat features in the newly created channel, such as placement ofwoody debris, riffles, vegetated bars, and/or small boulder clusters.
4. Grade the sediment within the impoundment on either side of the newly constructed channelto create constructed wetland habitat and vegetated riparian upland. The extent of excavation
will likely be influenced by the quality of the underlying sediment, which has yet to bedetermined. Another consideration will be the tolerance for physical disturbance along the
eastern portion of the project site in the area of existing scrub shrub wetland. A decision to
allow that area to naturally succeed to forested area or maintain a fringe of wetland can bemade as the design proceeds.
5. Protect the existing berm along Whalley Avenue as well as the bank that is located directlyacross from the spillway near the Walgreens parking lot through placement of fill, ideally
using excavated sediment that is relocated from the impoundment. Maintain the western
portion of the spillway as a core wall, to be cut off at grade to provide additional stability and
protection.
These preliminary recommendations will be refined once sediment testing data is available.
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POND LILY DAM ALTERNATIVES ANALYSIS
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1.0 INTRODUCTION
1.1 Project Background
Pond Lily Dam impounds the West River. The dam is physically located in the City of
New Haven; the impoundment extends into the Town of Woodbridge near the MerritParkway overpass. The dam and pond are owned by the New Haven Land Trust, whichoperates and maintains the impoundment as the Pond Lily Preserve.
The Pond Lily Dam was constructed in the late 1700s as a source of mechanical power
for a grist mill. The grist mill was succeeded by a carriage factory (in use during theCivil War) and later converted to a paper factory. The site was still used by industry up
to the 1970s. In the 1990s, the factory was demolished and the present retail center
located downstream of the dam was constructed, with land set aside for a 14-acre openspace parcel. The dam consists of an earthen berm and a 191-foot long, six-foot high
spillway over which water is conveyed to the downstream reaches of West River.
The Town of Woodbridge has retained Milone & MacBroom, Inc. (MMI) to analyze
design alternatives and evaluate the ecological impacts and benefits associated with full
or partial removal of the Pond Lily Dam. The dam is physically located within the City
of New Haven. The impoundment and upstream watershed extends north into the Townof Woodbridge. Modification of this structure is being evaluated for the purpose of river
restoration and improved fish passage, while maintaining the sustainable ecological
function of the large wetland area associated with the impoundment. Figure 1-1 is alocation plan of the project area.
1.2 Project Goals and Objectives
The following goals and objectives have been identified for the removal of Pond LilyDam and restoration of the West River in the area of the Pond Lily impoundment. These
have been formulated in conjunction with local, state, and federal project partners and
serve as a benchmark measure for the effectiveness of each of the alternatives evaluatedat this site. They are as follows:
1. Restore the river habitat to a more natural environment.2. Enable passage of target fish species, including alewife, blueback herring, and American eel.3. Provide flood relief for residents of Woodbridge Flats with additional flood storage
created with the removal of Pond Lily Dam.
4. Mitigate liability associated with failure of Pond Lily Dam via breaching or removal.5. Maintain or enhance habitat in the project area.6. Promote recreational use Pond Lily Nature Preserve.
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ProjectLocation
PondLilyDamA
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ativesAnalysis
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07/28
189
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Scale:
Date:
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1 inch
Pond Lily Impoundment Downstream
of Regal Motel Crossing
Pond Lily Dam Spillway
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1.3 Previous Studies
A number of studies have been previously conducted of the West River and its
impoundments to assess hydrodynamics, and habitat quality (fish passage) and floodmitigation. More specifically, the Pond Lily Dam has been the subject of many reports
related to flooding upstream of the impoundment around the Woodbridge Flats as well asrestoration of fish passage in the West River. A summary of critical study findings andrecommendations included below in chronological order. A complete list of resources is
included in Appendix A.
West River Flood Control Study (Flaherty Giavara Associates for the City of New Haven,
January, 1978) This engineering report includes a hydraulic analysis as well as
improvement studies for the West River downstream of the Pond Lily Dam.
Improving Fish Passage in the West River: Alewife and Blueback Herring Passage at the
Pond Lily Dam (Apse, C., Burchsted, D., Robbins, C., Triplett, T., for Advanced Applied
Hydrology course at Yale School of Forestry and Environmental Studies, May, 1999) This detailed fish passage study includes an overview of fish passage on the West River,
the target fish species for fish passage restoration, a history and existing conditions of the
Pond Lily Dam, and outlines a two phase fish passage restoration project evaluating
alternatives for downstream channel restoration and fish passage over Pond Lily Dam.This report provided the background analysis for the installation of the current fish ladder
at the dam.
Pond Lily Dam Inspection Report (Milone & MacBroom, Inc., May, 2000) This dam
inspection report documents the condition and potential hazards associated with PondLily Dam in 2000, which provides insight into the dam stability and any changes in the
condition since 2000.
West River: Restoration Plan for the Reach between Blake Street and Whalley Avenue.
(Casado, C., Gilbert, H., Karres, N., for River Processes Course at Yale School of
Forestry and Environmental Studies, December, 2008) This planning documentprovides a valuable description of the West River watershed including hydrology and
channel design parameters, which will help inform the design of a restored West River
channel surrounding the Pond Lily Dam.
Flood Study of Woodbridge Flats (Cardinal Engineering Associates, Inc., December,
2009) This engineering report includes a hydraulic analysis as well as alternative
analysis for flood mitigation for the West River from Konolds Pond in Woodbridge tothe Pond Lily Dam in New Haven. The study shows that removal or improvement of
structures downstream of the Merritt Avenue Bridge would not decrease flooding in the
Woodbridge Flats area. Instead, this report recommends removal or lowering of the PondLily Dam to restore fish passage and decrease upstream flooding during high flow events
in this section of the West River.
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POND LILY DAM ALTERNATIVES ANALYSIS
WEST RIVER; NEW HAVEN, CONNECTICUT
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Pond Lily Dam Evaluation and Environmental Assessment (Adera, S., Allan, N., Baldwin,
J., Piana, M., for River Processes Course at Yale School of Forestry and Environmental
Studies, December, 2009) This assessment report provides a detailed description,
including sediment classification, of existing conditions at the Pond Lily impoundment,Pond Lily Dam, and the channel downstream of the dam, as well as an evaluation of the
ramifications of a no action alternative, a dam repair alternative, and a dam removalalternative on sediment, flooding, wetlands, fish passage, recreation, and dam safety.
Flood Insurance Study, City of New Haven, CT, New Haven County This report
indicates the methods and flows used to determine the location and elevation of the 100-
year floodplain on the West River.
1.4 Current Phase Work Scope
Milone & MacBroom, Inc. (MMI) has been retained by the Town of Woodbridge to plan and
design the removal of Pond Lily Dam. The following specific work items are being
undertaken as part of this phase of work.
Existing Data Collection and Review On-Site Assessment of the Spillway and Dam On-Site Assessment of Ecological Communities Sediment Probing and Sampling Field Survey and Base Mapping Hydrologic and Hydraulic Assessment Evaluation of Dam Removal Alternatives Preliminary Engineering Design Public Outreach and Stakeholder Meetings
Future efforts will undertake regulatory permitting, final design, and construction phases ofthe project.
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2.0 EXISTING ENVIRONMENT
2.1 The West River An Overview
The West River watershed is 34.6 square miles in area covering land in the towns of
Prospect, Bethany, Hamden, and Woodbridge and the City of New Haven, Connecticut. Theheadwaters of the West River are located in Bethany just south of the border with Prospect.The river flows south for approximately 18 miles from its headwaters to end at the
confluence with Long Island Sound via West Haven Harbor. The West River watershed is a
sub-regional watershed included in the South Central Western Complex along with the Mill
River, a slightly smaller watershed with similar land use patterns that begins in the Town ofBethany and ends at the confluence with Long Island Sound in New Haven harbor, just to
the east of the mouth of the West River. Figure 2-1 illustrates the boundary of the West
River watershed as well as the boundaries of towns within and surrounding the watershed.
Table 2-1 below shows the land use in the West River watershed in 2006, along with
change in land use since 1985, according to data collected by the University of ConnecticutCenter for Land Use Education and Research. Similar with development and growth
patterns throughout the 20th and 21st centuries in nearby watersheds in Connecticut,
developed land in the watershed has increased by 182 acres (5.1%) between 1985 and
2006, indicating a likely associated increase in anthropogenic impacts on watershed landsand surface water bodies, including West River.
TABLE 2-1
Land Use in the West River Watershed
Land Use Type AcresPercent of
Total
Percent Change
since 1985
Developed 3763 32.2% 5.1%Turf & Grass 927 7.9% 10.8%
Other Grasses 94 0.8% -32.1%
Agricultural Field 166 1.4% -12.1%
Deciduous Forest 5369 45.9% -3.5%
Coniferous Forest 389 3.3% 1.6%
Water 429 3.7% -3.8%
Non-Forested Wetlan 54 0.5% 0.4%
Forested Wetland 197 1.7% -8.1%
Tidal Wetland 110 0.9% -4.8%
Barren 90 0.8% 44.8%
Utility (Forest) 102 0.9% -3.0%
As would be expected based on the high percentage of developed and managed land in the
West River watershed, flow in the West River is managed to a great extent and thefloodplain and channel itself are impacted by many impoundments and bridges for the
length of the river. The river is a free-flowing channel at its headwaters for the first mile
until it reaches Lake Bethany, the first of three dammed water supply reservoirs managedby the South Central Connecticut Regional Water Authority (SCCRWA).
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West River Watershed Boundary
(Drainage Area = 34.6 Square Miles)
Pond Lily Dam
Pond Lily Dam Contributing Drainage Basin
(Drainage Area = 16.6 Square Miles)
H a m d e nH a m d e n
B e t h a n yB e t h a n y
O r a n g eO r a n g e
N e w H a v e nN e w H a v e n
W o o d b r i d g eW o o d b r i d g e
C h e s h i r eC h e s h i r e
N o r t h H a vN o r t h H a v
W e s t H a v e nW e s t H a v e n
B e a c o n F a l l sB e a c o n F a l l s
N a u g a t u c kN a u g a t u c k P r o s p e c tP r o s p e c t
A n s o n i an s o n i a
D e r b yD e r b y
e y m o u re y m o u r
E a s t H a E a s t H a
W a l l i n g fW a l l i n g f
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Lake Bethany is followed by Lake Watrous and Lake Dawson. South of the Lake Dawsondam, the West River forms the western boundary of West Rock Ridge State Park for
approximately a mile before flowing into Konolds Pond, a popular fishing pond for local
residents. Konolds pond was impounded by a dam that was largely removed, leaving onlya spillway that remains as a fish passage barrier during low flow periods in the river. Figure
2-2 illustrates the location of these impoundments along the length of the West River.
Approximately one-half mile south of Konolds Pond, the West River enters the
impoundment formed by the Pond Lily Dam. Figure 2-1 illustrates the boundary of the
contributing drainage area above this dam. Between Konolds Pond and the Pond Lily Dam
the river channel is continuously constrained by various flood control structures maintainedby neighboring private land owners. The channel passes under five bridges before reaching
the Pond Lily impoundment: the Bradley Street Bridge, the Merritt Avenue Bridge, the
Route 15 Bridge, the Pond Lily Avenue Bridge, and the Regal Motel Bridge. Figure 2-3illustrates the location of the bridges between Konolds Pond and the Pond Lily Dam.
The reach of the West River downstream of the Pond lily dam for approximately 600 feet isdescribed in detail in Section 2.6 of this report as it relates to fish passage and natural river
design. The remainder of this overview of the West River was obtained from the Pond LilyDam Evaluation and Environmental Assessmentcompleted as a course requirement for the
River Processes course at the Yale School of Forestry and Environmental Studies (detailedreference information included in Appendix A).
Downstream of Pond Lily Dam, the channel passes beneath the East Ramsdell StreetBridge and then flows approximately 3,000 feet parallel to Whalley Avenue before bending
to the north under the Valley Street Bridge and forming the border of West Rock RidgeState Park for approximately 3,000 feet. After flowing under the Blakely Street Bridge the
channel is confined by a concrete canal for approximately 800 feet. Halfway down the
canal Wintergreen Brook, which drains the portion of the West River watershed to the eastof the West Rock ridge, converges with the main channel. At the end of the canal the river
flows under the Whalley Street Bridge and returns to more natural river channel conditions.
According to the Pond Lily Dam Evaluation and Environmental Assessment, the West
River flows through the City of New Haven as a natural channel intermittently confined by
local development and flood control efforts. Immediately south of the West River Park the
river flows under the Boston Post Road Bridge (also referred to as the Orange StreetBridge) where tide gates are located to manage tidal flooding and salt water intrusion. An
effort is currently underway to re-establish tidal flow to this southern section of the West
River to improve water quality, upstream vegetation, fish passage, and instream habitat.South of the tide gates, the river meanders at low velocities for approximately one mile
before flowing beneath Interstate 95 and entering New Haven Harbor at Kimberly Avenue.
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West River Watershed Boundary
(Drainage Area = 34.6 Square Miles)
Pond Lily Dam
(Project Location)
Lake Bethany
Lake Watrous
(SCCRWA Reservoir)
Lake Dawson
(SCCRWA Reservoir)
Konold's Pond
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reet base map from Microsoft Virtual Earth via ESRI
ubscription service
Pond Lily Dam Alternatives Analysis
New Haven, CTFigure 2-3: West River Bridges
Between Konolds Pond and Blake Street
LOCATION:
Bradley Street Bridge
Merritt Avenue Bridge
Route 15 Bridge
Regal Motel Bridge
Pond Lily Dam
East Ramsdell Street Bridge
Valley Street Bridge
Blake Street Bridge
OURCE:
99 Realty Drive Cheshire, CT
(203) 271-1773 Fax: (203) 272www.miloneandmacbroom
P:\Fig 2-3.mxd
1899-08
July 28 2011
Scale:
Map By:
MMI#:
MXD:
SJB
Date:
1 in = 1,500 ft
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2.2 Pond Lily Dam
The Pond Lily Dam extends
approximately 430 feet from the eastside of Whalley Avenue (State Route
69) to the far side of the pondabutting the New Haven Land Trustproperty accessed via Genesse Street.
Approximately 250 feet of the dam is
an earthen berm that is topped with a
concrete wall for 190 feet and a stonewall for 60 feet before reaching the
spillway. The spillway, at an
elevation approximately two feetlower than the earthen berm, is
approximately 192 feet long and six
feet high.
A pre-fabricated fish ladder is located in the western end of the spillway (right bank
looking downstream. The fishway was designed and installed in the early 2000s to aid
fish passage of anadromous and resident fish species including alewife and bluebackherring. The report summarizing these fish passage improvements, entitledImproving
Fish Passage in the West River: Alewife and Blueback Herring Passage at the Pond Lily
Dam by the Yale School of Forestry includes many details of the dam construction as aportion of the dam was exposed and removed during the ladder installation. The
following is an excerpt from this report documenting the condition of the dam in 1999:
The bottom 32 of the spillway is stone masonry. The remaining top portion is
composed of 5 thick concrete wall and rock fill. The crest of the spillway slopes
downward at a slope of 1:5.8 from the downstream face into Pond Lily. Overall the
spillway is in fair condition, with some missing stones and broken pieces in the upper
concrete wall.
A dam assessment was also included in the field inspection summarized in the Pond LilyDam Evaluation and Environmental Assessmentcompleted ten years later, in 2009. This
report also documents many structural weaknesses of the spillway, stating:
It appears that maintenance on Pond Lily Dam has not been conducted since the
textile dying factory facility was discontinued in the 1970s. As a result, many of the
rocks in the spillway have been displaced, causing multiple holes to form along the
length of the dam.
Subsequently, Pond Lily Dam was inspected on March 6, 2011 by MMI staff following
two to three inches of rain on top of thick snow cover, resulting in statewide peak flows
with two- to 10-year average return frequencies. The site visit was timed to coincide with
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JULY 2011 2-7
peak flow rates along the West River. High water marks were measured andphotographed in order to plot the flood profile. The following observations were noted:
1. The tailwater at the west end of the Pond Lily Dam was submerging the crest andalmost all of the fish ladder. The water level measured at 2.2 feet below the right
concrete abutment wall.
2. The pool headwater was 2.0 feet below the top of the right concrete abutment wall,near a four-inch drain pipe.
3. The east end of the spillway was flowing at a depth of about 1.25 feet, but tailwaterwas lower, reflecting a lateral gradient in the tailrace.
4. Water levels in the channel behind the Walgreens pharmacy were 6.0 feet below theupstream top corner of the gabion wall (marked with an orange paint spot). The
channel had full width steady flow at about four feet per second. Water levels at the
East Ramsdell Street box culverts were 2.4 feet below the top of the culvert opening.
5. The pool level at the midpoint of the dam was 1.5 feet below the top of a concretepad at the former outlet works (marked with an orange paint spot).
6. Moderate seepage with fine sand was discharging through the low concrete blockretaining wall at the bank's drive-through lane, indicating that there is internal
"piping" and erosion of core material. This should be monitored, as it is a seriousfault. The adjacent earth dam embankment has a 12-inch by 12-inch sinkhole (dry)
and irregular crown due to internal erosion and settlement.
7. Pond levels were 1.5 to 2.5 feet below the crest of the narrow earth dike alongRoute 69. Clear water seepage was present along the toe of dike.
8. River water was barely flowing below the Regal Motel Bridge (green I-beams)without surcharge and was 0.4 feet below the flange of the upstream beam at thebridge midpoint. Water was 4.1 feet below the low roadway curb, which is 0.9 feet
high.
9. Rapid flow water levels at the downstream side of the Pond Lily Avenue twin spanbridge was one foot below the beam bottom and 7.7 feet below the top of the 2.7
foot high parapet, at an orange paint spot. The upstream side of the bridge had
about a one-foot head loss at the pier, and shallow water was over the Route 15eastbound entrance ramp (bridge #06024).
10. Water upstream of Pond Lily Avenue and under the Route 15 elevated viaduct wasfairly tranquil, reflecting a backwater condition. Water under Route 15 reached half
way (horizontal) between the pier and Route 69 shoulder to the guy wire anchor
(orange paint spot).
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JULY 2011 2-8
11. At the Merritt Avenue Bridge, tailwater was 1.6 feet below the top of curb (at orangepaint spot) and 0.7 feet below the top of the upstream curb. Water was splashing
over the curb; bridge was flowing full under pressure. A Woodbridge police officerreported water levels were at their peak for the day. A slight road sag is located just
east of the bridge. The upstream channel was full and just over the banks.
12. The river was generally over its banks and onto the floodplain upstream of MerrittAvenue. Water was in contact with the foundations of two houses at the west end
of Manila Avenue.
13. Water levels at Bradley Road were above the east end of the bridge deck, and theroad was closed. The waterway was flowing full under low pressure. No detour
routes were posted, and several drivers asked for help going to pick up children.
14. Many residential and commercial buildings along Litchfield Turnpike (Route 69)between Merritt Avenue and Bradley Street were in the water including #1663,#1669, #1673, #1679, #1681, #1707, and #1711. Additional commercial and
industrial buildings along Bradley and South Bradley Roads were flooded such as
Abel's Catering and the Children's Garden.
The following findings were made based on this dam inspection:
1. Pond Lily Dam is in poor condition and unsafe due to spillway masonry "pop outs"of rock material and significant seepage through the earth embankment. The latter
is causing internal piping, settlement, and a sinkhole. The condition of the damwarrants inspection during each major rainfall.
2. Any significant increase in seepage or soil "piping" warrants emergency repairs oremergency breaching.
3. If the dam is not formally repaired or removed in 2011 before winter, seriousconsideration should be given to partially breaching the dam and draining the
impoundment.
4. The Merritt Avenue Bridge is scheduled for replacement. Because of its observedpressure flow and upstream flooding, the new structure should be designed to have
a thin cross section or even be a "through girder" type of bridge to minimize beams
that extend into the waterway.
5. There are only two vehicle accessways across the river to the WoodbridgeCommerce Park and Manila Avenue-Miles Avenue-Merritt Avenue neighborhoods,and both are subject to flood closure.
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WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 2-9
6. During the March 2011 flood, the Bradley Road Bridge was signed as being closedand flooded, and only the Merritt Avenue Bridge was open. There were no detour
signs to Merritt Avenue and no signage on how to cut across from Manila Avenue
to South Bradley Road. An improved signage system would be beneficial.
The following recommendations are offered:
1. Pond Lily Dam is in poor condition and has at least three potential failure modesthat could impact downstream areas. They are, in order of likelihood: a dike
breach along Whalley Avenue due to overtopping or seepage; a main embankment
breach near the bank drive-through lane due to seepage; or a structural erosionfailure of the spillway.
2. The dam should be monitored during "flood warnings" and when discharges at thenearby Mill River gauge in Hamden exceed 1,800 cfs (USGS Real Time Water
Data for USGS 01196620 Mill R Near Hamden, Connecticut).
3. An alert should be initiated if: The rate of seepage increases or is highly turbid (brown water) If water levels reach within one foot of the top of dike along Whalley Avenue If water levels reach within 0.5 feet of the top of the concrete wall between the
pond and bank building
If tailwater levels reach the top of the fish ladder frame4. In the event of a dam safety alert, contact:
City of New Haven: 911 City of New Haven City Engineers office: 203-787-6417 CT Department of Environmental Protection Dam Safety Unit: 860-424-3333,
860-424-3706
New Haven Land Trust: 203-562-66555. In the event of a dam safety alert:
Consider covering seepage areas with a sand and gravel filter and weight Consider using sand bags or fill to raise the dam or dike Consider evacuating the areas between the dam, Whalley Avenue, and East
Ramsdell Street, including the bank and retail shopping center Consider closing the northbound lanes of Whalley Avenue to reduce traffic
vibration and hazards
Pond Lily Dam was inspected by MMI staff again on May 11, 2011 at a slightly lower
water elevation. The structural concerns regarding the earthen berm and spillway were
confirmed, as additional displaced stones were observed at the base of the spillway.
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JULY 2011 2-10
2.3 Preliminary Wetland Assessment
On June 1, 2011 Matthew Sanford, a professional wetland scientist with Milone &MacBroom, Inc., completed an ecological evaluation of the wetlands and uplands
associated with the Pond Lily impoundment. Prior to conducting the field assessment, allpertinent maps, reports, and surveys were reviewed as an aid in evaluation of the site.
The ecological evaluation included walking the various wetland and upland habitats
within and surrounding the pond. Vegetation surveys were completed by visual
encounter method, which includes the identification of plants by leaves, bark, twigs, fruit,and flowers. Wildlife data was collected by visual encounter and auditory survey
methods which includes the identification of wildlife by tracks, feces, fur deposits,
feathers, burrows, nests, and habitats.
The most current USDA-NRCS soil survey mapping was gathered from the NRCS web
soil survey (http://websoilsurvey.nrcs.usda.gov ). A copy of the web soil survey mappingis included as Appendix B. The soil units mapped for the project site include Branford,
Udorthents, Rippowam, and water. The upland soils are derived from glaciofluvial
deposits. They consist of stratified sand and gravel. The parent material of these soils is
acidic red sandstone, shale, and conglomerate.
The Branford series consists of very deep, well drained soils formed in loamy over
sandy and gravelly outwash. They are nearly level to strongly sloping soils on outwashplains and terraces. Slope ranges from 0 to 15 percent. Saturated hydraulic conductivity
is moderately high or high in the solum and high or very high in the substratum. Much ofthe acreage is used for cultivated crops, hay and pasture. Common crops are silage corn,
vegetables, tobacco, and nursery stock. Some areas are wooded or used for community
development. Common trees are white, black and red oak, hickory, gray birch, whitepine, hemlock and white ash.
The soil mapping unit Udorthents and/or Urban Land is used to describe soils thathave been substantially disturbed including areas that have been excavated or filled by at
least two feet.
The wetland soils are derived from glaciolacustrine deposits. They consist of stratifiedsand and gravel. The parent material of these soils is acidic red sandstone, shale, and
conglomerate.
The Rippowam series consists of very deep, poorly drained loamy soils formed in
alluvial sediments. They are nearly level soils on flood plains subject to frequent
flooding. Slope ranges from 0 to 3 percent. Saturated hydraulic conductivity ranges frommoderately high or high in the loamy upper part and high or very high in the underlying
sandy materials. Most areas are in brushy woodland. Common trees are red maple,
willow, and alder.
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The wetland and watercourse resources present within the project site are described herein
using the U. S. Fish and Wildlife Service's wetland classification system described inClassification of Wetlands and Deepwater Habitats of the United States (Cowardin, et al.,
1979). Pond Lily impoundment and its associated wetlands within the project limits belong
to the palustrine ecological unit. In addition to wetland cover types, the upland cover typeswill be described. The following cover types are present within the project site:
Palustrine Open Water (POW) Palustrine Emergent Marsh (PEM) Palustrine Scrub Shrub (PSS) Palustrine Forested (PFO) Upland Shrub/Meadow (UPS/M) Upland Forested (UPLFO)
The vegetation cover types are represented on Figure 2-4.
Palustrine Open Water
The POW cover type includes those areas that
have open water present and that supportsubmerged and/or floating aquatic vegetation.
The open water areas support spatterdock lily,
white water lily, duckweed, and Eurasian watermilfoil. Table 2-2 provides a list of plant species
observed within the POW.
TABLE 2-2Palustrine Open Water
Scientific Name Common Name
Herbaceous
Nuphar lutea Yellow spatterdock lily
Nymphaea alba White water lily
Lemna minor Duckweed
Myriophyllum spicatum Eurasian watermilfoil*
Note: * = Nonnative Invasive Plant Species
Open Water Areas U/S of Dam
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S
a
n
d Original Pool Edge
Legend
Original Pool Edge
Existing Vegetation Cover Types
Palustrine Emergent Marsh (PE
Palustrine Forested (PFO)
Palustrine Scrub Shrub (PSS)
Upland Forested (UPLFO)
Upland Shrub/Meadow (UPS/M
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JULY 2011 2-13
PSS along west shoreline of Pond Lily
Palustrine Emergent Marsh
The PEM includes those areas that
support emergent and wet meadow plantspecies. Some shrubs may be intermixed
amongst this vegetation type. Typicallythis cover type is found at water depthsranging from one inch to two feet. Pond
lily has several large patches of PEM.
Table 2-3 provides a list of plant species
observed within the PEM.
TABLE 2-3
Palustrine Emergent Marsh
Scientific Name Common Name
Shrubs
Cornus amomum Silky dogwood
Cephalanthus occidentalis Buttonbush
Alnus rugosa Speckled alder
Herbaceous
Justicia americana Water willow
Typha latifolia Broad leaved cattail
Iris pseudacorus Yellow flag iris*
Scirpus pungens Woolgrass
Scirpus validus Soft stem bulrush
Carex stricta Tussock sedge
Lythrum salicaria Purple loosestrife*Sagittaria latifolia Duck potato
Sparganium americanum American burreed
Note: * = Nonnative Invasive Plant Species
Palustrine Scrub Shrub
The PSS includes those areas that support a
predominately thick shrubby stratum with
trees under 20 feet in height. Most of thesecover types have hummocky topography
with the high hummocks being vegetated
with shrubs and herbaceous material and thepits a combination muck and/or standing
water. There are several large swaths of PSS
that border the PEM's within the
impoundment. Table 2-4 provides a list ofplant species observed within the PSS.
PEM in foreground with PSS in background
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JULY 2011 2-14
TABLE 2-4
Palustrine Scrub Shrub
Scientific Name Common Name
Trees
Acer rubrum Red Maple
Quercus palustris Pin Oak
Ulmus americana American elm
Ulmus fulva Slippery elm
Robinia pseudoacacia Black locust
Shrubs
Salix discolor Pussy willow
Cornus amomum Silky dogwood
Cephalanthus occidentalis Buttonbush
Vaccinium cormybosum Highbush blueberry
Salix sericea Silky willow
Ilex verticillata Winterberry
Clethra alnifolia Sweet pepperbsuh
Alnus rugosa Speckled alder
Herbaceous
Symplocarpus foetidus Skunk cabbage
Thelypteris palustris Marsh fern
Impatiens capensis Jewelweed
Juncus effusus Soft rush
Carex stricta Tussock sedge
Onoclea sensibilis Sensitive fern
Toxicodendron radicans Poison ivy
Fallopia japonica Japanese knotweed*
Note: * = Nonnative Invasive Plant Species
Palustrine Forested
The PFO includes those areas that
support woody vegetation that is greaterthan 20 feet in height and an over story
canopy with at least 30 percent coverage.
PFO are the most common cover typefound within Connecticut. Table 2-5
provides a list of plant species observed
within the PFO.
PFO located along eastern portion of Pond Lily
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JULY 2011 2-15
TABLE 2-5
Palustrine Forested
Scientific Name Common Name
Trees
Robinia pseudoacacia Black Locust
Platanus occidentalis Sycamore
Acer rubrum Red Maple
Fraxinus pennslyvanica Green ash
Quercus palustris Pin Oak
Ulmus americana American elm
Shrubs
Lonicera americana American honeysuckle
Viburnum dentatum Northern arrowwood
Ilex verticillata Winterberry
Clethra alnifolia Sweet pepperbush
Cornus amomum Silky dogwood
Rosa multiflora Multiflora rose*
Berberis thunbergii Japanese barberry*
Herbaceous
Symplocarpus foetidus Skunk cabbage
Impatiens capensis Jewelweed
Juncus tenuis Path rush
Viola sp Violets
Carex stricta Tussock sedge
Carex crinita Fringed sedge
Onoclea sensibilis Sensitive fern
Arisaema triphyllum Jack in the pulpit
Trillium erectum Trillium
Toxicodendron radicans Poison ivy
Parthenocissus quinquefolia Virginia creeper
GrassesNote: * = Nonnative Invasive Plant Species
Upland Forested
Upland forested areas are found east of
Pond Lily. The forested cover type isclassified as a mixed hardwood forest.
Table 2-6 provides a list of plant
species observed within the UPLFO.
Upland forested area
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JULY 2011 2-16
Earthen berm located along Whaley Ave.
TABLE 2-6
UplandForested
Scientific Name Common Name
Trees
Robinia pseudoacacia Black Locust*
Platanus occidentalis Sycamore
Acer rubrum Red Maple
Acer saccharum Sugar maple
Prunus serotina Black cherry
Quercus palustris Pin Oak
Quercus rubra Red oak
Quercus velutina Black oak
Quercus alba White oak
Betula populifolia Grey birch
Carya ovata Shagbark hickory
Ailanthus altissima Tree of heaven*
Carpinus caroliniana American hornbeam
Shrubs
Lonicera morrowii Morrow's honeysuckle
Hamemalis virginia Common witch hazel
Cornus amomum Silky dogwood
Rosa multiflora Multiflora rose*
Berberis thunbergii Japanese barberry*
Ligustrum vulgare European privet*
Herbaceous
Thelypteris noveboracensis New York fern
Impatiens capensis Jewelweed
Juncus tenuis Path rush
Rubus allegheniensis Common blackberry
Toxicodendron radicans Poison ivy
Parthenocissus quinquefolia Virginia creeperVines
Celastrus orbiculatum Oriental Bittersweet*
Vipes sp. Grape
Smilax sp catbrier
Note: * = Nonnative Invasive Plant Species
Shrub/Meadow
This cover type consists of those areas that are
maintained as meadow, lawn, and have
sporadic shrub clusters. This cover typeprimarily occurs along the earthen berm
located along Whaley Avenue. Dense vinescover many of the trees and are choking thetrees. Also a patch of common reed
(Phragmites australis) is growing on the
berm. Table 2-7 provides a list of plant
species observed within the US/M.
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TABLE 2-7
UplandShrub/Meadow
Scientific Name Common Name
Trees
Robinia pseudoacacia Black Locust*
Acer rubrum Red Maple
Acer saccharum Sugar maple
Quercus palustris Pin Oak
Ailanthus altissima Tree of heaven*
Acer platanoides Norway maple
Shrubs
Lonicera morrowii Morrow's honeysuckle
Cornus racemosa Grey stemmed dogwood
Cornus amomum Silky dogwood
Rosa multiflora Multiflora rose*
Herbaceous
Onoclea sensibilis Sensitive fernImpatiens capensis Jewelweed
Phragmites australis Common reed
Fallopia japonica Japanese knotweed*
Toxicodendron radicans Poison ivy
Parthenocissus quinquefolia Virginia creeper
Vines
Celastrus orbiculatum Oriental Bittersweet*
Vipes sp. Grape
Smilax sp catbrier
Note: * = Nonnative Invasive Plant Species
Wetlands and watercourses possess the capacity to perform a variety of ecological andsocietal functions. These vary depending on the specific characteristics of the wetland
and/or watercourse being evaluated. The wetlands and watercourses within the project
limits were evaluated in order to identify the functions that they provide. Pond Lily andits associated wetlands provide a variety of functions including:
Floodwater Storage Export of Detritus Nutrient and Toxicant Removal Wildlife Habitat Shoreline Stabilization Fish HabitatTable 2-8 provides a summary of the functions and values of the watercourses andwetlands on site.
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JULY 2011 2-18
TABLE 2-8
Pond Lily and Associated Wetlands Functions and Values Assessment
Functions and ValuesComments
Groundwater Recharge / DischargeNo no ground water discharges (seeps)
observed.
Floodflow Alteration (Storage &
Desynchronization)
Yes Pond Lily and associated wetlands
located within FEMA-designated 100-
year flood zone.
Fish & Shellfish HabitatYes brook supports warm-water fish
species and anadromous species.
Sediment / Toxicant RetentionYes sediment deposition (alluvial
deposits) occurs behind dam.
Nutrient Removal / Retention /Transformation
Yes nutrient removal capabilities are
present within emergent and scrub shrubwetland areas - high stem density present.
Production Export (Nutrient)Yes Pond Lily exports allochthonous
materials to downstream habitats.
Sediment / Shoreline Stabilization Yes Pond Lilies banks are stable.
Wildlife Habitat
Yes narrow riparian zone along
impoundment but diversity of wetland
communities provide good wildlife
habitat.
Recreation (Consumptive & Non-
Consumptive)
Yes Lily Pond is owned and maintained
by the New Haven Land Trust so area isopen to public. There are no boat access
points. People observed fishing from
bridges.
Educational Scientific Value No
Uniqueness / Heritage No
Visual Quality / Aesthetics No
ES Endangered Species No
The principal functions/values of this system within this watershed are flood flowalteration, shoreline stabilization, wildlife habitat, nutrient and toxicant removal, fishery
habitat, and production export.
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2.4 Wildlife Assessment and Fishery Resources
As part of the ecological evaluation, MMI collected wildlife data by visual encounter and
auditory survey methods, which includes the identification of wildlife by tracks, feces,fur, feathers, pellets, rubbings, burrows, nests, and habitats. The major categories of
wildlife identified are described below. Observed species are listed in Table 2-9.
Mammals The site supports typical suburban species common to the river corridor such
as white tailed deer, eastern chipmunk, common raccoon, Virginia opossum, gray
squirrel, striped skunk, ground hog and a variety of other small rodents. MMI observed
deer and deer tracks plus fur, scat, trails, and rubbings. Chipmunks and gray squirrelswere observed in the forested areas. Raccoon tracks were noted along the muddy areas
found within the forested wetland. Minor excavations typical of skunks were noted.
Tiny burrows typical of mice, voles, and moles were also observed.
Birds The site supports typical suburban species common to the corridor such as
Canada goose, mallard, American robin, common crow, woodpeckers (downy, red-bellied, and yellow-shafted flicker), European starling, common grackle, red winged
blackbird, catbird, house sparrow, Northern cardinal, black-capped chickadee, tufted
titmouse, white-breasted nuthatch, song sparrow, American goldfinch, and blue jay.
Reptiles and Amphibians The site supports typical suburban species common to the
corridor such as painted turtle, snapping turtle, Eastern garter snake, green frog,
American bullfrog, American toad, and red-backed salamander. Standing water ispresent in many locations within the scrub shrub wetlands, however given the
shallowness of the standing water and the urbanized setting no obligate vernal poolspecies were observed within the wetlands on site.
Fishery Resources The West River and Pond Lily supports a variety of fish speciesincluding pumpkinseed, bluegill, largemouth bass, brown bullhead, white sucker,
American eel, blueback herring, and American shad.
TABLE 2-9
Wildlife Inventory
Mammals
Scientific Name Common Name
Didelphis virginiana Opossum
Marmota monax Ground hog
Mephitis mepitis Striped skunkOdocoileus virginianus White-tailed deer
Procyon lotor Raccoon
Sciurus carolinensis Gray squirrel
Tamias striatus Eastern chipmunk
Miscellaneous rodents
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TABLE 2-9 (Cont.)
Wildlife Inventory
Birds
Agelaius phoeniceus Red winged blackbird
Anas platyrhynchos Mallard
Archilochus colubris Ruby-throated hummingbird
Baeolophus bicolor Tufted titmouse
Branta canadensis Canada goose
Buteo jamaicensis Red-tailed hawk
Cardinalis cardinalis Northern cardinal
Carduelis tristis American goldfinch
Colaptes auratus Northern flicker
Columba livia Rock dove
Corvus brachyhynchos Common crow
Cyanocitta cristata Blue jay
Melanerpes carolinus Red-bellied woodpecker
Melospiza melodia Song sparrow
Mimus polyglottos Northern mockingbird
Passer domesticus House sparrow
Picoides pubescens Downy woodpecker
Poecile atricapillus Black-capped chickadee
Quiscalus quiscula Common grackle
Sayornis phoebe Eastern phoebe
Sitta carolinensis White-breasted nuthatch
Sturnus vulgaris European starling
Tachycineta bicolor Tree swallow
Turdus migratorius American robin
Zenaida macroura Mourning dove
Reptiles
Bufo americanus American toad
Chelydra serpentina Snapping turtleChrysemys picta Painted turtle
Nerodia sipedon Northern water snake
Thamnophis sirtalis Eastern garter snake
Amphibians
Hyla versicolor Grey tree frog
Plethodon cinerens Redback salamander
Pseudacris crucifer Spring peepers
Rana catesbeiana American bullfrog
Rana clamitans melanota Green frog
2.5 West River Downstream of Pond Lily Dam
A geomorphic assessment of the reach of the West River extending downstream of thePond Lily Dam was performed on May 11, 2011. The channel parallels the dam spillway
for 125 feet moving from right to left at a width of about 20 feet. The left bank for this
segment consists of the Pond Lily Dam. The earthen berm that forms the right bank forthis river reach appears to be constructed, most likely to protect the bordering
development. The berm is likely constructed of rip rap, with cement blocks that may
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POND LILY DAM ALTERNATIVES ANALYSIS
WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 2-21
have been re-used from walls demolished during the redevelopment of the surroundingparcels.
Towards the southern end of this river segment, a depression was observed in the top ofthe berm. It is possible that this is a sink hole due to incomplete compaction of the berm
during construction, or it could be inundated and scoured during high flow eventsrepresenting a flood chute over the berm. Lack of flood debris and flow indicatorssignify that the sink hole is the more likely scenario, a factor considered when designing
alternatives for the downstream channel configuration post-dam removal.
The channel bed for this segment of river is composed entirely of angular placedboulders. Due to the composition, large size, and angular nature of these boulders, it is
unlikely that they are native river rock; they were most likely placed during construction
of the berm, fish ladder construction, and redevelopment of neighboring parcels in orderto reinforce the dam. Scour
pools have formed between
these boulders up to four feetdeep in some locations.
After approximately 125 feet,
the channel turns west toparallel the gabion-enforced
banks along the Walgreens
parking lot and driveway areaon the right bank and the New
Haven Land Trust Pond LilyPreserve and day care center on
the left bank. At approximately
160 feet across the dam from theend closest to Whalley Avenue
the right bank begins with
stacked rip rap composed ofboulders with a four-foot diameter in places. The elevated area formed by the rip rap is
vegetated with black locust trees that appear to be 20 to 30 years in age. Behind the rip
rap, the gabion wall begins 20 feet downstream of the dam on the right bank and ends
approximately 280 feet downstream of the dam. On the left bank downstream of thegabion basket wall, the bank is fortified with placed rip rap until a small floodplain forest
forms at 600 feet downstream of the dam. In the river segment immediately downstream
of the dam, the gabion wall is composed of four layers of stacked three-foot-tall gabionbaskets that are slightly tapered (approximately six inches per layer). The bottom-most
gabion was almost completely buried, with only the top six inches visible above the
channel bed at the time of inspection. The gabion baskets range from four to five feethorizontal.
Segment of West River beginning 125 downstream of
Pond Lily Dam. Note non-native rock in channel and
gabion basket walls on both banks.
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The top of the bank is thickly vegetated on the left bank. Shrub and tree species observedincluded multiflora rose (Rosa multiflora), sugar maple (Acer saccharum), honey locust(Gleditsia triacanthos), sycamore (Plantanus occidentalis), American elm (Ulmus
Americana), basswood (Tilia sp.), aspen (Populus sp.) and thick Virginia creeper(Parthenocissus quinquefolia), honeysuckle (Lonicera sp.), with poison ivy
(Toxicodendron radicans)in some locations. Knotweed (Fallopia japonica) andsensitive fern (Onoclea sensibilis) were observed growing within the active channel
width. The left bank is vegetated with similar species in a 20-foot thick riparian buffer
beginning approximately 400 feet downstream of the dam.
While significant scour and undercutting were observed on the face of the berm oppositethe spillway, the southern face of the berm on the right bank in this location appears to
accumulate sediment during high flow events as evidenced by accumulation of debris on
the rip rap and a sand and gravel bar at the toe of the slope. It is possible that a smallbackwater area forms in this location as the thalweg of the channel is directed toward the
left bank. This is further evidenced in pictures from the flood event documented on
March 7, 2011.
For the reach of the river contained within the gabion baskets, the channel is
homogenous. The bed is composed of large non-native rock that has a mean diameter of
approximately eight-inches. The rocks are interlocked throughout this river segment withno small particle deposition (not embedded or armored). There were no clear bankfull
indicators on this river segment due to the constructed banks and recent record flood
(March 7, 2011). However, there is a clearly defined thalweg in the center of the channelthat forms an active channel that is approximately 10 feet wide when vegetation has filled
in during the low flow period of the summer months. The riparian corridor was litteredwith a remarkable amount of garbage in this segment of the river.
Two constructed weirs were observed approximately 300 feet and 500 feet downstreamof the dam. These will be evaluated to determine if they are additional fish passage
barriers. At the time of field inspection, there was flow over both weirs sufficient for fish
passage. There was no deposition of sand or gravel in this segment of the river thatwould provide preferred fish spawning habitat.
The measured slope of the channel from the dam to the first weir was 1.22% and from the
first weir to the second weir was 2.97%. Two storm water drainage outfalls with flaps wereobserved conveying flow from the Walgreens development located 300 feet and 400 feet
downstream of the dam respectively.
The observed channel form changed significantly downstream of the second constructed
weir at approximately 600 feet downstream of the dam. Both natural banks are vegetated
with a 50% slope and thick knotweed growth on the right bank leading up to the pavedarea and a forested floodplain on the left bank. The estimated bankfull width at this
location is 60 feet wide. Channel bed materials consist of sand and coarse gravel,
indicating that this is the first sediment storage reach downstream of the dam. This
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WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 2-23
section of the river may be considered as a reference reach for natural channeldimensions for West River in the project area.
2.6 Sensitive Species Review
The area surrounding the Pond Lily Dam is shown within a Connecticut NaturalDiversity Data Base (NDDB) polygon, indicating that sensitive species have beenidentified in the general area. On May 26, 2011, a request was made to the Connecticut
Department of Environmental Protection through the formal NDDB review process. A
copy of the request is included in Appendix C. As of the writing of this document, a
response had not yet been received.
2.7 Sensitive Historical/Archeological Resources
On May 26, 2011, formal inquiries were made to the State Archeologist, Dr. Nicholas
Bellantoni, and the State Historic Preservation Office via the Connecticut Commission on
Culture and Tourism requesting information on archeological resources in the area ofPond Lily Dam to determine whether the sit has the potential to contain archeological
resources. Copies of the letters are included in Appendix D. As of the writing of this
document, responses had not yet been received.
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WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 3-1
3.0 SEDIMENT ANALYSIS
3.1 Overview
Most man-made ponds and lakes accumulate river-borne sediments, and Pond Lily is no
exception. Based on inspection of historical imagery from 1934, 1951, 1991 and 2008, itappears that the accumulation of sediment behind the Pond Lily Dam is slowing fillingPond Lily, as evidenced by the decreasing area of open water in the images.
The character of the sediment is influenced by the five upstream Regional Water
Authority reservoirs that trap much of the river's heavier sand and gravel sediment whileallowing fine grain silt and clay to move further downstream. Pond Lily receives the
pass-through silt and clay, along with sand from Route 69 and Route 15 (Merrit Parkway)
and local sediment from soft, reddish New Haven Arkose (sandstone-like) bedrock in thearea. The dominant West Rock ridge is composed of tough basalt-like dolerite. The
sediments on Pond Lily are varied depending on location, but most common are loose to
moderately dense cohesive fine grain material. The upstream end of the pond has ahigher percentage of sand and gravel, as would be expected.
Two sediment samples were collected in September 2010 by Princeton Hydro, Inc. and
analyzed by Phoenix Environmental Laboratories, Inc. of Manchester Connecticut. Thesamples were analyzed for volatile organic compounds (VOCs), various metals, cyanide,
PCBs, total petroleum hydrocarbons, total organic carbon, hexavalent chromium and
semi-volatile compounds (SVOCs), pesticides and herbicides. The analytical methodsappear to have been selected in order to evaluate the environmental quality of the
sediment in regards to ecological risk as opposed to providing information relative todisposal or reuse options, should the sediment be removed.
The 2010 sediment analytical results suggest the presence of contaminants typical of urbanstormwater runoff, although the levels do exceed those typically allowed for commercial
areas located in GA classified groundwater zones. Based upon the results, the primary
constituents of concern include the potential for leachable metals and for the group of semi-volatile organic compounds referred to as polynuclear aromatic hydrocarbons (PAHs).
However, the nature and extent of sediment impacts can not be determined based upon the
limited analytical methodologies employed in 2010. Additional analytical data is required
to identify options and to better estimate costs associated with sediment management duringdam removal. Such testing is planned as part of the current phase of work.
3.2 Summary of 2011 Sediment Probing
Sediment probing throughout the impoundment was conducted by MMI in an effort to
characterize the sediment that has accumulated behind the Pond Lily Dam since itsconstruction. The sediment depth, type, and shear strength was identified at approximately
60 locations. The results of this analysis were then plotted on aerial photography to assess
deposition patterns, and to identify locations for further sediment investigation.
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WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 3-2
Sediment probing was completed using a manually operated steel rod. Results wererecorded using a Trimble GPS unit that was calibrated and corrected using WAAS
technology such that points could be recorded at sub-meter accuracy. Undrained shear
strength was measured in-situ using a manually operated vane shear test device tocharacterize the resistance to erosion the sediment will provide upon dam removal.
Figure 3-1 presents the sediment types identified. Where water velocities were highest atthe head of the impoundment, sediments consisted mostly of sand with trace amounts of
silt. Downstream of this sandy zone was a transition area where sediment consisted of a
mixture of sand and silt. Sediments in the remainder the impoundment where lower
velocities allow smaller particles to settle can be characterized by "muck," reflective of
silt with some clay and high organic content.
Figure 3-2 presents the depths of sediment measured at each location. Depths ranged from
zero to greater than 60 inches. The quantity of sediment in the active channel was estimatedbased upon the measured sediment depths and is presented in Table 3-1. These quantities
do not include the sediment that has been deposited in the heavily vegetated fringe areas.
TABLE 3-1
Estimated Sediment Volume
Type Quantity (CY)
Muck 6,600
Sandy Muck 700
Sand 4,200
During the probing, an attempt was made to locate the historic river channel. Former
channel areas tend to exhibit thicker fine grained deposits, with refusal on native bedmaterial occurring one to several feet lower than adjacent probe locations. Additionally,the filled channel substrate is often underlain by larger diameter native substrate (i.e.
cobbles and boulders) that are indicative of the historic channel armoring. These
conditions were recorded throughout the impoundment and plotted to approximate the
location of the historic river channel as indicated on Figure 3-2.
In-situ shear strength of the sediments varied by depth and sediment type. The sandy
sediments ranged between 150 and 300 pounds per square foot (psf) and did notsignificantly vary with depth. The organic, silt and clay matter ("muck") showed high
levels of consolidation with increasing depth, with shear strengths that increased by as
much as five times at a depth of 36 inches. Table 3-2 presents a summary of the datacollected. The values of mechanical shear strength represent a very weak material that is
prone to erosion. The mechanical shear strengths will be converted to hydraulic shear
stress and compared to the critical shear stress and predicted velocities once the full
hydraulic analysis is completed. The erodibility, along with the proposed channel designand placement will guide and shape the project's sediment management plan.
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S
a
n
d
Vegetation on
old sediments
A l d e r
&
D o
g w o o d Z o n e
Original Pool Edge
Legend
Original Pool Ed
Sediment Probing Locat
Muck
Sand
Sandy Muck
Sediment Type
Sand
Sandy Muck
Silt/Organic Muc
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Original Pool Edge
Probable Location of Historic River Channel
Legend
Original Pool E
Sediment Thickness
0.0 - 1.0
1.1 - 2.0
2.1 - 3.0
3.1 - 4.0
4.1 - 5.0
5+
Historic River Channel
Outline
Channel Area
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POND LILY DAM ALTERNATIVES ANALYSIS
WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2011 3-5
TABLE 3-2
Undrained In-Situ Sediment Shear Strengths
Type Depth
Mechanical Shear
Strength (PSF)
Muck 6" 80-100
Muck 36" 400-550
Sand 12" 150-300
3.3 Sampling Locations & Methodology
On behalf of the Town of Woodbridge and American Rivers, MMI has submitted a
Sediment Sampling Plan to the Connecticut Department of Environmental Protection for
review an input prior to sampling activities. Five vertically averaged sediment samplesare proposed to be collected and analyzed one downstream of the dam and four in the
upstream impoundment. The sample locations within the impoundment were selected to
refine the understanding of potential contaminants in the sediment and provideinformation that will subsequently be used to evaluate sediment reuse or disposal options.
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JULY 2011 4-1
4.0 HYDROLOGY
4.1 Hydrologic Analysis
The West River watershed has a total drainage area of 34.6 square miles, flowing from
north to south from Prospect to Long Island Sound at West Haven. The watershed area atthe Pond Lily Dam is 16.6 square miles. The watershed encompasses basin numbers5303, 5304, and 5305 on the CTDEP Natural Drainage Basins in Connecticut map
(CTDEP, 1981). Five Regional Water Authority (RWA) water supply reservoirs are
located in the central part of the watershed, known as Lakes Bethany, Watrous,
Chamberlain, Glen, and Dawson. The water supply safe yield and withdrawal rate for theRWA system in this watershed is 10.4 million gallons per day (mgd.
Flood control improvements were constructed in the lower West River watershed (belowPond Lily Dam) following extensive damage from the 1982 flood. Specific measures
included construction of additional box culverts at East Ramsdell Street, a new bridge at
Blake Street, and channel improvements from East Ramsdell Street to Pond Lily Damand from Whalley Avenue to Blake Street. An extensive freshwater wetland and then a
tidal marsh extends from Whalley Avenue to a tide gate at Boston Post Road.
Hydrologic information is available from several sources, which are summarized below.There are no USGS flow gauges in this watershed; however, water level measurements
are made at the Lake Dawson Reservoir spillway by the Regional Water Authority.
4.2 Flood Flows
Existing Data The 1991 FEMA Flood Insurance Study for Woodbridge contains
hydrology information for the peak flow rates predicted for flood events with an average
return frequency of 10, 50, 100, and 500 years. Hydrology was analyzed by the U.S. SoilConservation Service (SCS) using the TR-20 computer model. Results are reported in
Table 4-1. The watershed area at Lily Pond Avenue is 16.4 square miles; at Lake
Dawson, it is 13.9 square miles. The recently issued New Haven County Flood InsuranceStudy includes both New Haven and Woodbridge and repeats the 1991 data. The 1978
West River Flood Control Study by Flaherty Giavara Associates lists a 100-year
frequency flood flow of 3,003 cfs at Pond Lily, based upon a 1976 SCS study. The
CTDEP Gazetteer of natural drainage area reports a watershed area of 16.6 square milesat Pond Lily and 13.9 at Lake Dawson, consistent with the FEMA study.
USGS Regression Equations U.S. Geologic Survey hydrology regression equationswere accessed via the internet StreamStats software to predict low and peak flow rates at
Pond Lily, using updated precipitation data. The equations do not consider reservoir
storage or water supply withdrawals. The results are shown in Table 4-1. The reportedwatershed area is 17.1 square miles, which is higher than the FEMA watershed area.
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POND LILY DAM ALTERNATIVES ANALYSIS
WEST RIVER; NEW HAVEN, CONNECTICUT
JULY 2