66622832 66604826 draft alternatives analysis july 2011

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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

WEST RIVER; NEW HAVEN, CONNECTICUT

JULY 2011 i

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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JULY 2011 ii

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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JULY 2011 iii

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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JULY 2011 ES-1

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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JULY 2011 ES-2

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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JULY 2011 ES-3

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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JULY 2011 ES-4

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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JULY 2011 1-1

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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JULY 2011 1-3

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 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


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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


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

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JULY 2011 2-6

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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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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JULY 2011 2-11

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


24/64

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


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


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


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


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


Onoclea sensibilis Sensitive fern

Toxicodendron radicans Poison ivy

Fallopia japonica Japanese knotweed*


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


Trees

Robinia pseudoacacia Black Locust

Platanus occidentalis Sycamore


Fraxinus pennslyvanica Green ash


Ulmus americana American elm

Shrubs

Lonicera americana American honeysuckle

Viburnum dentatum Northern arrowwood

Ilex verticillata Winterberry

Clethra alnifolia Sweet pepperbush


Rosa multiflora Multiflora rose*

Berberis thunbergii Japanese barberry*

Herbaceous

Symplocarpus foetidus Skunk cabbage


Juncus tenuis Path rush

Viola sp Violets


Carex crinita Fringed sedge

Onoclea sensibilis Sensitive fern

Arisaema triphyllum Jack in the pulpit

Trillium erectum Trillium


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


Trees

Robinia pseudoacacia Black Locust*

Platanus occidentalis Sycamore


Acer saccharum Sugar maple

Prunus serotina Black cherry


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



Berberis thunbergii Japanese barberry*

Ligustrum vulgare European privet*

Herbaceous

Thelypteris noveboracensis New York fern


Juncus tenuis Path rush

Rubus allegheniensis Common blackberry


Parthenocissus quinquefolia Virginia creeperVines

Celastrus orbiculatum Oriental Bittersweet*

Vipes sp. Grape

Smilax sp catbrier


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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JULY 2011 2-17

TABLE 2-7

UplandShrub/Meadow


Trees

Robinia pseudoacacia Black Locust*


Acer saccharum Sugar maple


Ailanthus altissima Tree of heaven*

Acer platanoides Norway maple

Shrubs

Lonicera morrowii Morrow's honeysuckle

Cornus racemosa Grey stemmed dogwood



Herbaceous

Onoclea sensibilis Sensitive fernImpatiens capensis Jewelweed

Phragmites australis Common reed

Fallopia japonica Japanese knotweed*


Parthenocissus quinquefolia Virginia creeper

Vines

Celastrus orbiculatum Oriental Bittersweet*

Vipes sp. Grape

Smilax sp catbrier


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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JULY 2011 2-19

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


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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JULY 2011 2-20

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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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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JULY 2011 2-22

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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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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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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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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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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66622832 66604826 draft alternatives analysis july 2011

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