Massabesic Lake Dam

EXECUTIVE SUMMARY

[This section should consistMASSABESIC of a narrative that provides anLAKE executive summary DAM of this inspection report. At a minimum this section should include the following:

· Name ofINSPECTION dam and town / EVALUATION REPORT · Date of inspection · Name of Engineering Consultant completing the inspection · Condition of the dam (Good, Satisfactory, Fair, Poor, Unsafe – choose one, do not use “Fair to Poor”) · Brief summary of major deficiencies · Brief summary of activities since the last inspection · Brief summary of major recommendations

Immediately following this section should be the Dam Evaluation Summary Detail Sheet that will be used by the Office of Dam Safety to update the database. This sheet is generated automatically from the inspection checklist. Modifications to the setup of this form shall not be made. An example of this form is shown.]

Dam Name: Massabesic Lake Dam

State Dam ID#: 150.06

NID ID#: NH 00103

Owner: Manchester Water Works

City: Manchester, NH

Consultant: Wright-Pierce

Date of Inspection: September 20, 2016 EXECUTIVE SUMMARY

This Inspection/Evaluation Report details the inspection and evaluation of the Massabesic Lake Dam (#150.06) located in the Manchester Water Works, Hillsborough County, New Hampshire. The inspection was conducted on September 20, 2016 by Wright-Pierce.

Massabesic Lake Dam is currently classified as an Intermediate; Class C structure – High Hazard Potential dam.

1. Damaged chain link fence extending downstream on left training wall and missing railings 2. Leakage at intersection of downstream spillway and left training wall and downstream spillway face. 3. Deteriorated concrete on spillway crest and abutments. 4. Vegetation and brush growth in downstream discharge channel and along left and right training walls. Debris and vegetation on spillway approach and around upper gate chamber. Vegetation and brush growth on upstream granite stone walls 5. Top of embankment asphalt roadway deterioration, ruts, sink hole and vegetation growth 6. No access to spillway bays to monitor and clean debris. 7. Operation and integrity of upper chamber gates and trash racks unknown. 8. Cracked mortared granite stone wall joints. 9. Upstream dry laid stone wall movement, missing/loose stones 10. Unable to locate two downstream pipes.

There were no detailed hydrologic and hydraulic analyses (H&H) available for this dam; as such, the capacity of the current spillway to accommodate the Spillway Design Flood (SDF) is unknown.

The Operations and Maintenance Plan and Emergency Action Plan were reviewed and need to be updated.

Wright-Pierce recommends that the following actions be taken to address the deficiencies found at the dam during the inspection and evaluation:

1. Perform detailed H&H with recommendations to modify the spillway to pass the SDF as required. 2. Perform a Structural and Stability analyses including subsurface investigations as needed with recommendations to modify the spillway as required. 3. Update Operations and Maintenance Plan and Emergency Action Plan. 4. Repair spalling and deteriorated concrete on spillway crest and abutments. 5. Repair granite stone upstream and downstream training walls. 6. Repair damaged chain link fence and replace missing guard rails. 7. Provide access to the spillway bays. 8. Revise flashboards to be collapsible. 9. Develop a long term plan to draw-down the impoundment so the upstream granite stone dry laid stone walls and upper gate chamber trash racks and gates can be inspected.

The repairs and recommendations noted above and described in more detail herein should be made in accordance to standard design practices, specifications and construction methods. Design of the repairs

Massabesic Lake Dam Date of Inspection: September 20, 2016 and analyses to confirm the extent or the work should be completed by a qualified professional engineer experienced in the design and rehabilitation of dams throughout the evaluation, design and construction process. Opinions of probable repair costs are provided within this report.

Massabesic Lake Dam Date of Inspection: September 20, 2016 PREFACE

The assessment of the general condition of the dam reported herein was based upon available data and visual inspections. Detailed investigations and analyses involving hydrologic/hydraulic studies, stability analyses, subsurface investigations, and underwater investigations are beyond the scope of this evaluation unless otherwise noted.

In reviewing this report, it should be realized that the reported condition of the dam was based on observations of field conditions at the time of inspection, along with data available to the inspection team.

It is critical to note that the condition of the dam depends on numerous and constantly changing internal and external conditions, and is evolutionary in nature. It would be incorrect to assume that the reported condition of the dam will continue to represent the condition of the dam at some point in the future. Only through continued care and inspection can there be any chance that unsafe conditions be detected.

______

Walter J. Flanagan III, P.E. New Hampshire License No.: 07246 License Type: Structural Vice President Wright-Pierce

Massabesic Lake Dam Date of Inspection: September 20, 2016 TABLE OF CONTENTS

Page No.

EXECUTIVE SUMMARY

DAM EVALUATION SUMMARY DETAIL SHEET

PREFACE

SECTION 1

1.0 DESCRIPTION OF PROJECT 1

1.1 General 1 1.1.1 Authority 1 1.1.2 Purpose of Work 1 1.1.3 Definitions 1

1.2 Description of Project 1 1.2.1 Location 1 1.2.2 Owner/Caretaker 2 1.2.3 Purpose of Dam 2 1.2.4 Description of the Dam and Appurtenances 2 1.2.5 Operations and Maintenance 3 1.2.6 Size Classification 3 1.2.7 Hazard Potential Classification 3

1.3 Pertinent Engineering Data 4 1.3.1 Drainage Area 4 1.3.2 Reservoir 4 1.3.3 Discharges at the Dam Site 4 1.3.4 General Elevations (Feet) 4 1.3.5 Main Spillway Data 5 1.3.6 Design and Construction Records and History 5 1.3.7 Operating Records 8

1.4 Summary Data Table 9

SECTION 2

2.0 INSPECTION 9

2.1 Visual Inspection 10 2.1.1 General Findings 10 2.1.2 Dam 10 2.1.3 Appurtenant Structures 12 2.1.4 Canal 12 2.1.5 Downstream Area 12 2.1.6 Reservoir Area 13

Massabesic Lake Dam Date of Inspection: September 20, 2016 TABLE OF CONTENTS

Page No.

2.2 Caretaker Interview 13

2.3 Operation and Maintenance Procedures 13 2.3.1 Operational Procedures 13 2.3.2 Maintenance of Dam and Operating Facilities 14

2.4 Emergency Warning System 14

2.5 Hydraulic/Hydrologic Data 15

2.6 Structural and Seepage Stability 16 2.6.1 Embankment Structural Stability 16 2.6.2 Structural Stability of Non-Embankment Structures 16 2.6.3 Seepage Stability 16

SECTION 3

3.0 ASSESSMENTS AND RECOMMENDATIONS 17

3.1 Assessments 17

3.2 Studies and Analyses 17

3.3 Recurrent Maintenance Recommendations 18

3.4 Minor Repair Recommendations 18

3.5 Remedial Modification Recommendations 18

3.6 Alternatives 19

3.7 Opinion of Probable Construction Cost 19

FIGURES

Figure 1: Locus Plan Figure 2: Aerial Plan Figure 3: Drainage Area Figure 4: Dam and Downstream Area Figure 5: Plan

APPENDICES

Appendix A: Photographs Appendix B: Inspection Checklist

Massabesic Lake Dam Date of Inspection: September 20, 2016 TABLE OF CONTENTS

Page No.

Appendix C: Historical Illustrations Appendix D: Existing Drawings Appendix E: Previous Reports and References Appendix F: Definitions

Massabesic Lake Dam Date of Inspection: September 20, 2016

Section 1

SECTION 1

1.0 DESCRIPTION OF PROJECT

1.1 General

1.1.1 Authority

Manchester Water Works retained Wright-Pierce to perform a visual inspection and develop an Inspection/Evaluation report of conditions for the Massabesic Lake Dam in Manchester, Hillsborough County, New Hampshire.

1.1.2 Purpose of Work

The purpose of this investigation was to inspect and evaluate the present condition of the dam and appurtenant structures to provide information that will assist in both prioritizing dam repair needs and planning/conducting maintenance and operation.

The investigation was divided into four parts: 1) obtain and review available reports, investigations, and data previously submitted to the owner pertaining to the dam and appurtenant structures; 2) perform a visual inspection of the site; and; 3) evaluate the status of an emergency action plan for the site and 4) prepare and submit a final report presenting the evaluation of the structure, including recommendations and remedial actions, and opinion of probable costs.

1.1.3 Definitions

To provide the reader with a better understanding of the report, definitions of commonly used terms associated with dams are provided in Appendix F. Many of these terms may be included in this report. The terms are presented under common categories associated with dams which include: 1) orientation; 2) dam components; 3) size classification; 4) hazard classification; and 5) miscellaneous.

1.2 Description of Project

Sections of this report are based upon available documentation, including previous inspection reports and other available information as identified in Appendix C, D and E. Other historical information obtained during the inspection, has been incorporated into this report. This material is intended to provide general information. The accuracy of this referenced information was not verified as it was outside the scope of work for this inspection.

1.2.1 Location

Massabesic Lake Dam is located in the Manchester, Hillsborough County, New Hampshire about 3,000 feet southwest of the natural outlet of Massabesic Lake known as Coffer Dam, State ID #150.16 (Class AA – Non Menace). Massabesic Lake consists of two large ponds joined at Deer Neck Bridge on Londonderry Turnpike Route #28 Bypass. The East Pond (Front Pond) is located on the eastern side of the bridge is within the Town of Auburn, NH while the West Pond (Back Pond) on the western side of the bridge is divided North and South by the Auburn-Manchester town lines. The center of the dam spillway is located at coordinates latitude 42.9630 North and longitude -71.39550 West. From the Auburn Traffic Circle, head south on Candia Road 1 Massabesic Lake Dam Date of Inspection: September 20, 2016 approximately 1.6 miles, turn left on to E Industrial Park Drive, proceed approximately 1.2 miles. Turn right onto Island Pond Road and proceed approximately 120 feet and turn left onto Cohas Ave. Continue on Cohas Ave for approximately 0.8 miles and turn left onto Canal Ave. Follow the road for approximately 0.4 miles until it meets Hermit Road, the Dam is on the left.

The Massabesic Lake Dam drainage area is approximately 47 square miles within the City of Manchester and the Towns of Auburn, Hooksett, Candia and Chester, New Hampshire. The discharge from Massabesic Lake Dam flows into the Great Cohas Brook, a tributary of the Merrimack River.

The location of Massabesic Lake Dam and impoundment are shown in Figure 1: Locus Plan. An aerial photograph of the dam is provided as Figure 2: Aerial Plan

1.2.2 Owner/Caretaker

The dam is currently owned, maintained and operated by the Manchester Water Works. See Table 1.1 for current owner and caretaker data (names and contact information).

1.2.3 Purpose of the Dam

As indicated in Table 1.1, the dam is used for water supply and limited recreational use. The dam controls the level of Massabesic Lake and directs water to a pump station/hydroelectric facility on Cohas Avenue during high flow events.

1.2.4 Description of the Dam and Appurtenances

Massabesic Lake Dam (State ID #150.06) as shown in Figures 5: is a concrete and granite stone masonry dam with earth embankments and a canal with earth embankments built in 1873. The Dam consists of three major components; the spillway, the right and left earth embankments, and the canal outlet structure

The dam has a maximum structural height of approximately 29.5 feet and a hydraulic height of approximately 25.5 feet. No water was flowing over the dam or through the low level outlet pipe during the inspection. The pond level was approximately 4 feet below normal operating level.

The concrete ogee spillway is approximately 100 feet wide with four concrete piers spaced equally. In the past, the Canal Ave continued across a wooden bridge over the spillway. The spillway crest is at elevation 248.93 feet. 18-inch high permanent flashboards span across the spillway. A 30-inch diameter outlet pipe is located on the left side of the spillway at the base of the dam. On the downstream face, granite stone masonry training walls direct the flow into the Great Cohas Brook.

The left and right embankment crests are about 22 feet wide and supports an abandoned paved roadway. The embankment crests are at elevation 254.52 feet. The downstream slope of both earth embankments grassed. The Massabesic Lake Dam, NH 00103, Phase I Inspection Report National Dam Inspection Program”, Department of the Army New England Division, Corps of Engineers, Waltham, MA 02154, Dated August 1978 indicated that the downstream embankment slopes were 1.5H:1V. Based on our observations, the downstream slopes are significantly shallower. It is uncertain if there are core walls in the earth abutments.

2 Massabesic Lake Dam Date of Inspection: September 20, 2016 The upstream face of the both earth embankments consist of vertical granite stone walls. The top several feet consist of mortared joints and the remaining portion of the wall is dry laid granite stone.

The right embankment (northeast of spillway) is approximately 125 feet long. At the end of the right embankment, there is a short curved which abuts an abandoned road. A granite stone wall continues parallel to the abandoned road in an easterly direction for approximately 360 feet and turns in northerly direction for approximately 45 feet.

The left embankment (southwest of spillway) is approximately 140 feet long. At the end of the left embankment there is a short curve which abuts Hermit Road and Canal Ave. The upper gate chamber is approximately 31 feet beyond the curved section which conveyors water to the canal and eventually to the hydroelectric/pump station.

The canal is approximately16 feet deep by 1,470 long and 35 feet wide at the bottom with approximately 1H:1V side slopes. The gate chambers at the upper and lower ends of the canal are protected by trash racks. At the lower end of the canal, water flows through the lower gate chamber into a 6-foot diameter steel penstock slip lined with a 54-inch HDPE pipe for approximately 625 feet long into the hydroelectric pump station

1.2.5 Operations and Maintenance

Massabesic Lake Dam is owned by the Manchester Water Works. Manchester Water Works is responsible for the operation and maintenance of the dam. John O’Neil, Watershed Forester for Massabesic Lake Dam is the primary caretaker. Operation and maintenance activities are described in Section 2.3.

1.2.6 Size Classification

Massabesic Lake Dam has a height of dam of approximately 29.5 feet and a maximum storage capacity of 16,583 acre-feet due to the restrictions upstream at Coffer Dam. Refer to Appendix F for definitions of height of dam and storage. Therefore, in accordance with the Corps of Engineers' Recommended Guidelines, the Massabesic Lake Dam is an Intermediate size structure.

1.2.7 Hazard Potential Classification

Massabesic Lake Dam discharges into Great Cohas Brook which flows westerly from the dam for approximately 6.8 miles, passing beneath and flowing beside I-93 at the 101/I-293/I-93 interchange about ¾ mile downstream. From there it enters a flat area about 1-mile long between S. Mammoth Road and Route 28. Then the stream valley narrows and steepens, draining into Pine Island Pond and joining the Merrimack River in a short steep drop under Route 3A at Goffs Falls.

It appears that a failure of the Massabesic Lake Dam at maximum pool, due to its location and size, would likely result in probable loss of human life and property damage. I-93 could be inundated. In addition to the flood hazard, the water supply for the City of Manchester would be severely reduced.

3 Massabesic Lake Dam Date of Inspection: September 20, 2016 Therefore, in accordance with New Hampshire Code of Administrative Rules, Parts ENV-WR 101.06 the Massabesic Lake Dam is "Class C structure" meaning the dam is a High Hazard Potential.

1.3 Pertinent Engineering Data

1.3.1 Drainage Area

The Massabesic Lake Dam drainage area is approximately 47 square miles with the City of Manchester and the Towns of Auburn, Hooksett, Candia and Chester, New Hampshire. The area is generally considered as “flat” terrain hydrologically.

The following dams are located within the drainage area;

#150.16 Coffer Dam (Class AA – Non Menace) #150.18 Sleggo Dam (Class AA – Non Menace) #13.03 Clark Pond East Dam (Class A – Low Hazard) #13.04 Clark Pond West Dam (Class A – Low Hazard) #13.09 Pengree Hill Mill Dam (Class A – Low Hazard) #13.01 Tower Hill Dam (Class C – High Hazard) 1.3.2 Reservoir

See Table 1.1 for data about normal, maximum and spillway design flood (SDF) reservoir volumes. The reservoir has an irregular shape.

1.3.3 Discharges at the Dam Site

No records of discharges from the dam site were made available.

1.3.4 General Elevations (feet)

Elevations are based on Massabesic Lake Dam, NH 00103, Phase I Inspection Report National Dam Inspection Program”, Department of the Army New England Division, Corps of Engineers, Waltham, MA 02154, Dated August 1978.

A. Top of Dam/Embankments Elevation 254.52 Feet B. Spillway Design Flood Pool Unknown C. Normal Pool Elevation 250.43 Feet D. Maximum Pool (1936 Flood) Elevation 253 Feet +- E. Spillway Crest Elevation 248.93 Feet F. Overall Length (including embankments) 365 +/- Feet G. Upstream Water at Time of Inspection Elevation 246.4 +- H. Downstream Water on 9/20/2016 No flow, Low Level Gate Closed I. Streambed at centerline of dam Elevation 225 Feet +-

4 Massabesic Lake Dam Date of Inspection: September 20, 2016 1.3.5 Main Spillway Data

A. Type Concrete Ogee B. Spillway Length 100 Feet +- C. Spillway Crest Elevation Elevation 248.93 Feet D. Height to Spillway Crest 24.0 Feet F. Flashboards 18” Permanent (non-failing) G. Downstream 30” Sluice Outlet Invert Elevation 226.8 Feet

1.3.6 Design and Construction Records and History

The original design and construction information for the dam is not available.

The following account of historical information is based upon available documentation, including previous inspection reports and other available information as identified in Appendices C, D and E. Other historical information obtained during the inspection, included information provided by the Owner, has also been incorporated. This material is intended to provide general information. The accuracy of this referenced information was verified to the extents possible through the investigations and evaluations completed as part of this study.

In 1872, the first Water Board for the City of Manchester designated Massabesic Lake as the best source of water supply for the City, and proceeded to acquire land around the lake and rights to the water.

In the 1873, the present dam was constructed along with the pumping station on Cohas Avenue was built, which housed the hydroelectric facility to supply some of the power for the pumps.

5 Massabesic Lake Dam Date of Inspection: September 20, 2016 Originally, the dam’s overall length was about 225 feet, width of top of banks about 22 feet and a total height of the dam was 28 feet. The waste-weir or overflow (spillway) was about 42 feet long constructed of granite stone masonry with a series of 7 steps on the downstream side to break the fall of the overflowing water, a fall of about 24 feet. The edges of the steps created an inverted parabolic curve. The crest was designed to be 2 feet below the normal full lake level and flashboards were used to maintain the surface at the best practical elevation. The downstream sides of the overflow were protected by mortared granite stone training walls. The earth embankments consisted of a center masonry priming wall 2.5 feet thick at the top and sloping 1 to 16. A riprap stone faced the upstream side, and lower side was grassed, both sloping 1.5 to 1. An 18-foot-wide carriage-bridge spanned the spillway and was supported by three intermediate piers.

A canal and penstock were constructed to divert water from the dam to a hydroelectric pump station. The canal was approximately16 feet deep by 1,470 long and 35 feet wide at the top. The gate chambers at the upper and lower ends of the canal had four gates each 3 feet wide by 5 feet high each protected by trash racks and fish screens. At the lower end of the canal, water flowed through the gate chamber into a 6-foot diameter wooden penstock for approximately 625 feet long into the hydroelectric pump station.

6 Massabesic Lake Dam Date of Inspection: September 20, 2016 Sometime after 1884, 30-inch high flash boards were installed.

About 1913, the 60-inch wooden penstock was replaced with a 60-inch steel penstock.

7 Massabesic Lake Dam Date of Inspection: September 20, 2016 In 1922, the crest was modified and raised 30” and 30-inch high flash boards continued to be used.

In 1931, the crest was modified again. Had it not been done, the dam would probably have suffered considerable damage in the flood of March 1936.

In 1945, the crest and downstream face was rebuilt into an ogee cross section with 8” high flashboards and the bridge piers and abutments were raised 1 foot which increased the spillway capacity further. The existing 3 foot by 5-foot low level outlet gate and sluiceway were modified and a 30-inch sluice gate was installed.

In 1974, a new 40 million gallons a day Water Treatment Plant was built on another part of the lake.

In 1975, vertical cracks on the downstream spillway face were repaired with epoxy sealant.

In 1978, the Army Corps of Engineers Phase 1 Inspection Report indicated that the dam was in poor condition due to structural cracking, embankment seepage and low spillway capacity.

In 1980, the wooden bridge spanning the spillway was destroyed by fire and not replaced.

In 1995, vertical cracks on the downstream spillway face and spalled concrete areas were repaired. The downstream spillway faced was coated with a waterproofing material.

About 2004/2005 the left and right downstream embankments were enlarged, regraded and the toe extended.

About 2008 the flashboards were replaced with 2- 9-inch high white oak boards.

In 2010, the sluice gate shaft and bearings were replaced and 60-inch steel penstock was slip lined with a 54-inch HDPE pipe.

1.3.7 Operating Records

Operating records that include inspection checklists, mowing schedules, gate operation logs and periodic monitoring reports are maintained.

8 Massabesic Lake Dam Date of Inspection: September 20, 2016

Section 2

SECTION 2

2.0 INSPECTION

2.1 Visual Inspection

Massabesic Lake Dam was inspected on September 20, 2016. At the time of the inspection, the temperature was 68 to 74 F with cloudy to partly sunny skies with a light wind. Photographs to document the current conditions of the dam were taken during the inspection and are included in Appendix A. The water level was approximate 48 inches below normal pond elevation. No water was passing over the spillway and the 30-inch sluice gate was closed. The upper gates to the canal were open and the hydroelectric power plant was not operating. A copy of the inspection checklist is included in Appendix B.

2.1.1 General Findings

In general, Massabesic Lake Dam was found to be in POOR condition due to the lack of original construction drawings and stability calculations, the uncertainty of the spillway being able to pass the design flood and deteriorated concrete, cracked mortared granite stone joints, dislodged dry laid granite stone walls and vegetation and brush growth. The specific concerns are identified in more detail in the sections below:

2.1.2 Dam

· Spillway The concrete ogee spillway appeared to be in poor condition. No water was flowing over the spillway. Four concrete piers equally spaced divide the spillway into 5 sections. Each concrete pier is approximately 1’-6” wide x 22 feet long and extends about 3’-11” above the spillway crest. The nose of the piers are reinforced with steel plates. The piers originally supported a wooden bridge. The alignment of the spillway and piers appear to be straight and true. The concrete surface of the ogee spillway and piers have spalled concrete and stone aggregate exposed. The spillway approach is covered with debris, vegetation and sediment.

The 18-inch permanent flashboards appear to be in good condition. To minimize leakage through the flashboards, a pvc sheet membrane has been wrapped up and over the flashboards and weighted down with masonry blocks.

No signs of movement, settlement or seepage was observed on the downstream face. Several hairline cracks were observed on the downstream face as well as efflorescent. Approximately 50 weep holes were observed in the downstream spillway face. Reportedly, when the reservoir is full several damp spots have been seen near the top of the downstream spillway face.

· Abutments Both concrete abutments appear to be stable and in fair condition. Weeds and small bushes were observed growing on the abutments. The concrete surface of the ogee spillway and piers have spalled concrete and stone aggregate exposed.

10 Massabesic Lake Dam Date of Inspection: September 20, 2016 · Left Earth Embankment (Southwest) The downstream slope of the earth embankment is in good condition and covered with grass. No signs of slope movement, erosion, animal burrows or seepage was observed. The vertical and horizontal alignments of the embankment are in good condition. Reportedly, around 2006 the embankment slope was enlarged, made less steep and the toe extended.

The embankment crest is about 22 feet wide and supports a paved roadway, Canal Ave with guard rails on each side. In the past, the roadway crossed over a wooden bridge on the spillway. The asphalt pavement is deteriorating. Some cracking, unevenness and vegetation growth was observed.

The upstream face of the earth embankment vertical granite stone wall and is in fair condition. The top several feet of the mortar joints need repair. The remaining portion of the wall is dry laid granite stone. The wall has moved overtime and voids are exposed. Brush and vegetation are growing out of the wall.

· Right Earth Embankment (Northeast) The downstream slope of the earth embankment is in good condition and covered with grass. No signs of slope movement, erosion, animal burrows or seepage was observed. The vertical and horizontal alignments of the embankment are in good condition. Reportedly, around 2006 the embankment slope was enlarged, made less steep and the toe extended.

The embankment crest is about 22 feet wide and supports an abandoned paved roadway. In the past, the roadway crossed over a wooden bridge on the spillway and connected to Canal Ave. The asphalt pavement is deteriorating. Some cracking, unevenness and vegetation growth was observed.

· Downstream Granite Stone Training Walls The mortared granite stone walls appear to be stable and in fair conditions. The alignment of the training walls appears to be straight and true. Several mortar joints need to be repairs. It appears that some of the joints have been repaired in the past.

Weeds and small bushes were observed growing on the face and backside of the training walls. Some leakage was observed at the bottom of the intersection of the downstream spillway and left training wall. The slopes directly behind the left and right training walls are quite steep and make it difficult to cut vegetation and bush.

11 Massabesic Lake Dam Date of Inspection: September 20, 2016 · Access Roads and Gates The dam is accessed directly from Canal Ave or Island Pond Road. There are no gates to prevent the Public from accessing the northeast or southwest embankments There are fences at each end of the spillway. The left abutment fence extending downstream is damaged and needs to be repaired.

· Drains No drains were observed during the inspection.

A 15-inch RC pipe with an invert elevation of 228.4 feet near the downstream right training wall was not located as referenced in the Massabesic Lake Dam, NH 00103, Phase I Inspection Report National Dam Inspection Program”, Department of the Army New England Division, Corps of Engineers, Waltham, MA 02154, Dated August 1978.

Reportedly, a drain pipe discharges near the downstream right embankment slope near the brook. This pipe begins near the abandoned road and woods on the right hand side of the northeast embankment. Riprap was observed, however the pipe outlet was not located.

· Instrumentation No instruments were observed at the dam.

2.1.3 Appurtenant Structures

· Low Level Outlet The 30” sluice gate is used as the primary outlet for controlling the lake level. The upstream end of the outlet pipe was underwater and not observed at the time of the inspection. The downstream end of the pipe was visible. The gate was closed on the day of inspection and no leakage downstream was observed. The gate discharges directly downstream into the Great Cohas Brook.

The sluice gate is operated by a Rodney Hunt manual operating stem. Reportedly, it operates infrequently.

2.1.4 Canal

The upper canal gate chamber was not observed. The condition of the trash racks and gates is unknown. The gates are raised and not used. The exact number and size was not confirmed. Brush and vegetation are growing around the upper gate chamber. The area is fenced. The center concrete wall on the upstream sides is severely spalled. The upper part of gate chamber is closed off with wood planking and the trash rack is below this. Some debris was observed on the Trash racks.

2.1.5 Downstream Area

12 Massabesic Lake Dam Date of Inspection: September 20, 2016 Massabesic Lake Dam discharges into the Great Cohas Brook which flows westerly from the dam, passing beneath and flowing beside I-93 at the 101/I-293/I-93 interchange about ¾ mile downstream. From there it enters a flat area about 1mile long between S. Mammoth Road and Route 28. Then the stream valley narrows and steepens, draining into Pine Island Pond and joining the Merrimack River in a short steep drop under Route 3A at Goffs.

The channel immediately downstream of the spillway is covered with sand, gravel and boulders. There are trees and brush growing in the channel.

2.1.6 Reservoir Area

All land around Massabesic lake is owned by the Manchester Water Works with limited recreation allowed.

No unusual conditions were observed upstream of the dam. The impoundment behind Massabesic Lake Dam extends roughly 3000 feet east and north of the dam to the natural outlet of Massabesic Lake known as Coffer Dam. The impoundment is located within rural area with undeveloped shoreline. The shoreline of the impoundment is mainly covered by trees and vegetation. The ground slopes gently down to the reservoir on the upstream side of the dam. The slopes along the perimeter of the impoundment are generally flat.

The reservoir is oriented in the east - west direction, flowing towards the west and has an irregular shape.

As indicated on available documents, the impoundment is approximately 20 feet at it deepest areas with an average depth of approximately 10 feet. The impoundment is restricted by the water depth at natural outlet at Coffer Dam. The bottom of the natural outlet at Coffer Dam is approximately 6.5 feet below the normal reservoir elevation.

2.2 Caretaker Interview

The Manchester Water Works is responsible for the operation and maintenance of the dam. John O’Neil, Watershed Forester for Manchester Water Works is the primary caretaker and was interviewed during the inspection on September 20, 2016. Information provided by John O’Neil has been incorporated into this report.

2.3 Operation and Maintenance Procedures

The operation and maintenance (O&M) was reviewed during the inspection. The dam and the appurtenant features are observed on a weekly basis by the dam caretaker. The dam is also inspected prior to, during, and after significant storm events. The observations are recorded documenting the condition of the crest, upstream and downstream slopes, spillway, outlet structures, and canal.

2.3.1 Operational Procedures

13 Massabesic Lake Dam Date of Inspection: September 20, 2016 Flashboards are permanently installed. The 30-inch sluice at the spillway gate is used to control the Lake level. In periods of excess runoff, the Manchester Water Works hydroelectric plant is operated to lower lake levels further. Lake withdrawals at the water treatment plant also assist in lowering and controlling lake levels. The Lake is not intentionally lowered during the winter months. No minimum flow downstream is required.

2.3.2 Maintenance of Dam and Operating Facilities

The embankments are mowed approximately twice per year in the late spring and late summer or as needed. Growth of trees and brush are maintained each spring. The embankment is maintained by filling ruts and depressions, and loamed and seeded each spring or as needed.

The permanent flashboards are repaired as needed. Debris is removed from the upstream, downstream and crest of the spillway on an as needed basis.

2.4 Emergency Warning System

The current EAP was last revised in February 2013. Copies of the emergency action plan (EAP) for the dam are kept at Manchester Water Works Office.

The dam is classified as a Class C structure - High Hazard Potential; therefore, development and maintenance of an Emergency Action Plan is required in accordance with New Hampshire Code of Administrative Rules, Parts ENV-WR 303.06 and in accordance with New Hampshire Code of Administrative Rules, Parts ENV-WR 507.01 is required to be tested, reviewed and updated every two years.

The EAP should be reviewed and updated accordingly addressing the following:

· Appendix A – Project Description: The project description provides only basic dam and watershed information and does not fully comply with the requirements of Env-Wr 505.07 Dam and Watershed Description. This information should be updated.

· Appendix B – Impact of Breach: The impact of breach narrative is very brief and it is unclear whether the impact to Interstate 93 is predicted to occur in both the Sunny Day and 100-yr Event breach conditions or just the 100-yr Event breach condition. There is also no mention of other areas that may be impacted (e.g. other roads that may be flooded, or overtopping at the Pine Island Pond Dam); however, there are other areas listed for evacuation and/or monitoring in Appendix E. The narrative in this section should be reviewed and updated/expanded.

· Appendix D – Training and Testing: The dam monitor contact information does not include a home or cell phone number. In the event that an emergency occurs outside of regular business hours an alternative contact phone number may be needed. This contact information should be updated.

· Appendix D – Training and Testing: The Dam Rules Env-Wr 507.01 requires that the Dam Monitor conduct a test of the notification procedure and emergency communication network

14 Massabesic Lake Dam Date of Inspection: September 20, 2016 every 2 years. Has this testing been conducted since the latest revision of EAP in February 2013? If this testing is due, the Owner should conduct a test and update the notification procedure and contact information if necessary.

· Appendix F – Posting of the Plan: The telephone numbers for several of the EAP holders are not currently included in this appendix. Dam Rule Env-Wr 505.11 List of Official EAP Holders states that telephone numbers should be provided in the contact information. This list should be reviewed and updated.

· Appendix F – Posting of the Plan: Dam Rule Env-Wr 505.11 List of Official EAP Holders states that the owner s of downstream dams that would be affected by a dam breach be included in the List of Official EAP Holders. The owners of the Pine Island Pond Dam are not included in Appendix F. If Manchester Water Works does not own the Pine Island Pond Dam, this list should be updated to include the correct owner information.

2.5 Hydrologic/Hydraulic Data

Massabesic Lake Dam is an Intermediate sized, Class C structure - High Hazard structure and in accordance with New Hampshire Code of Administrative Rules, Parts ENV-WR 303.11 the spillway design flood (SDF) for the site is 250% of the 100-year storm event (2.5 x storm). NHDES regulations require that the dam spillway be able to pass the 2.5 x storm with one foot of free board and no manual operation.

A detailed Hydrologic/Hydraulic analysis has not been completed for current configuration. Therefore, the ability of the discharge structure to accommodate the spillway design flood is not known.

Massabesic Lake Dam, NH 00103, Phase I Inspection Report National Dam Inspection Program”, Department of the Army New England Division, Corps of Engineers, Waltham, MA 02154, Dated August 1978 concluded that:

· the probable maximum flood (PMF) to be about 23,700 cfs inflow into Massabesic Lake and during the PMF, the peak outflow at the dam would be about 12,600 cfs (reduction from the peak inflow of 23,700 cfs being accounted for by the considerable surcharge storage effect of the lake).

· The spillway capacity (in 1978 with the bridge in place) was about 3,060 cfs or about 24% of the PMF. It was estimated that the dam would be overtopped by about 3.2 feet during the PMF.

· If the permanent flashboards were replaced with collapsible flashboards, the spillway capacity would be increase to 4,600 cfs or about 37% of the PMF. It was estimated that the dam would be overtopped by about 1.7 feet during the PMF

The Emergency Action Plan Update, Massabesic Lake Dam by HTE Northeast, Inc. dated September 2009 was reviewed.

· The Hydraulic and Hydrologic (H&H) modeling information provided does not include a Spillway Capacity Analysis. Based on review of the information provided, it is unknown whether or not the Massabesic Lake Dam can accommodate the Spillway Design Flood (SDF). In accordance with Dam Rule Env-Wr 303.11 Discharge Capacity, the spillway of the Massabesic Lake Dam shall pass 250% of the 100-yr flood, or at the owner’s option, the site 15 Massabesic Lake Dam Date of Inspection: September 20, 2016 specific inflow design flood. Any recommendations for repair work to “improve spillway capacity” will require that the H&H analysis for the dam be updated to including a spillway capacity analysis.

· The hydrologic modeling was developed utilizing HydroCAD (version 9.0) computer software. The model was run using the 100-yr, 24-hr, rainfall depth of 6.30 inches. While the use of this rainfall data meets the requirements for Hydrologic Investigations outlined in Dam Rule Env-Wr 403.05, there is updated rainfall data that could (and generally should) be used to update this model. The NRCC (Cornell) rainfall data predicts a rainfall depth of 7.85 inches for the 100-yr, 24-hr storm event and the NOAA Atlas 14 rainfall data predicts a rainfall depth of 7.12 inches for the 100-yr, 24-hr storm event. The NHDES Dam Bureau has not yet updated their rules to require the use of these newer rainfall datasets, but this update is something that will likely occur in the near future. The increased rainfall predicted in these newer datasets could result in an expanded inundation area in the event of a dam breach. The H&H analysis should be updated to incorporate newer rainfall data and the inundation maps should be updated accordingly.

· The H&H analysis provided does not include a description of the downstream boundary condition utilized in the HEC-RAS model. The HEC-RAS model appears to extend downstream of the Massabesic Lake Dam to the confluence of Cohas Brook with the Merrimack River. The model run for the 100-yr storm event (with and without a breach) should incorporate the 100-yr flood elevation in the Merrimack River to better simulate the extent of inundation. It is unclear whether or not this condition has been incorporated in the modeling effort.

· The inundation areas depicted on the maps should be reviewed to confirm that there has been no new development that could be at risk since these maps were developed in 2009.

2.6 Structural and Seepage Stability

No formal stability evaluations have been completed for this structure since the original design; no records of the original design computations were available for review at the time of the preparation of this report. Some historical illustrations for the dam were reviewed, providing some insight into the original construction.

2.6.1 Embankment Structural Stability

A soil stability analysis was not included in the scope of this report. The visual inspection of the side slopes indicated no visual signs of seepage or instability.

2.6.2 Structural Stability of Non-Embankment Structures

A structural stability analysis was not included in the scope of this report. The visual inspection of the spillway and Canal outlet structure indicated no visible signs of instability, movement or erosion.

2.6.3 Seepage Stability

A seepage analysis was not included in the scope of this report. The reservoir at the time of the inspections was approximately 4 feet below normal pool elevations. No seepage was observed.

16 Massabesic Lake Dam Date of Inspection: September 20, 2016

Section 3

SECTION 3

3.0 ASSESSMENTS AND RECOMMENDATIONS

3.1 Assessments

The following recommendations and remedial measures generally describe the recommended approach to address current deficiencies at the dam. Prior to undertaking recommended maintenance, repairs, or remedial measures, the applicability of environmental permits needs to be determined for activities that may occur within resource areas under the jurisdiction of local conservation commissions, NHDES, or other regulatory agencies

3.2 Studies and Analyses

The following studies or analyses are recommended to further evaluate concerns, and comply with current regulations. These studies and analyses shall be performed by a qualified professional engineer experienced dams and hydrology, maintenance and monitoring activities.

1. Perform a detailed hydrologic and hydraulic (H&H) analysis for the impoundment drainage area and spillway outlet capacity in regards to the spillway design flood. in accordance with New Hampshire Code of Administrative Rules, Parts ENV-WR 303.11 the spillway design flood (SDF) for the site is 250% of the 100-year storm event (2.5 x storm). NHDES regulations require that the dam spillway be able to pass the 2.5 x storm with one foot of free board and no manual operation.

2. Complete a structural and stability analysis of the spillway structure at the dam to determine the overall stability of this structure and extents of repair that maybe required.

17 Massabesic Lake Dam Date of Inspection: September 20, 2016 3. Prepare an updated Operations and Maintenance Manual.

4. Prepare an updated Emergency Action Plan (EAP)

5. Develop a long term plan to draw-down the impoundment so the upstream granite stone dry laid stone walls can be inspected and repointed/repaired as needed and inspect the canal upper gate chamber to determine the condition of the gates and trash racks.

3.3 Recurrent (Yearly) Maintenance Recommendations

1. Perform regular monitoring and inspection of; a. Earth embankment, b. Spillway, and including areas of observed concrete deterioration, c. Leakage through downstream spillway and intersection of left training wall and spillway, d. Unwanted vegetation development, e. Accumulation of debris or other areas of suspected movement or concerns, to check for signs of deteriorating conditions. As the dam is currently classified as a High Hazard Potential structure, formal inspections are required every two (2) years. 2. The 30-inch Sluice gate needs to be lubricated and operated on a monthly basis. 3. Regular maintenance activities should be continued to control and prevent further growth of unwanted vegetation, as was noted in areas during the inspection, as well as to remove debris from the spillway and trash racks, mowing grass and cutting brush should be performed at least twice per year (i.e., late spring and fall). All cuttings from brush and other vegetation should be removed from the site and properly disposed.

3.4 Minor Repair Recommendations

The following recommendations should be implemented to maintain the integrity and improve the overall condition of the dam but do not alter the current design of the dam. These recommendations may require design by a professional engineer and construction by a contractor experienced in dam construction or repair.

1. Remove vegetation and debris in discharge channel, behind downstream left and right training walls, along top of embankments and upper gate chamber 2. Repair damaged chain link fence and replace missing guard rails. 3. Repair deteriorate asphalt road or remove and grass along top of embankment and fill in sink hole.

3.5 Remedial Modification Recommendations

The following conceptualized modifications should be implemented to improve the safety and integrity of the dam and to extend the life of the structure. These recommendations will likely require design by a professional engineer and construction by a contractor experienced in dam repair.

1. Repair/reconstruction mortared and dry laid stone wall

18 Massabesic Lake Dam Date of Inspection: September 20, 2016 2. Install walkway over the spillway to provide access to spillway bays. 3. Revise flashboard to be collapsible. 4. Repair leakage at intersection of downstream spillway and left training wall and downstream spillway face. 5. Repair deteriorated concrete on spillway crest and abutments.

3.6 Alternatives

There are no practical alternatives to the recommendations provided above.

3.7 Opinion of Probable Construction Costs

The following conceptual opinions of probable costs have been developed for the recommendations and remedial measures noted above. The costs shown herein are based on limited investigation and are provided for general information only. This should not be considered an engineer's estimate, as construction costs may be less or considerably more than indicated. It is important to note that the recommendations from the H&H and Structural/Stability evaluations may have significant impact on the spillway/embankment improvements and construction costs.

Studies and Analyses 1. Hydrologic / Hydraulic Evaluation $18,000 - $27,000 2. Structural /Stability Evaluations $15,000 - $30,000 3. Update Emergency Action Plan $ 5,000 - $10,000 4. Update Operations & Maintenance Manual $ 4,000 - $ 5,000 Subtotal $42,000 - $72,000

Recurrent (Yearly) Maintenance Recommendations 1. Regular monitoring and inspection $4,000 - $6,000 2. Regular maintenance $3,000 - $6,000 Subtotal $7,000 - $12,000

Minor Repair Recommendations 1. Remove vegetation and debris in the discharge channel, Behind the downstream left and right training walls, along the top of embankments and upper gate chamber $2,000 - $ 4,000 2. Repair damaged chain link fence and replace missing guard rails. $1,500 - $ 3,000 3. Locate 15” Pipe on downstream side of Right training wall and drain located beyond the right training wall. $1,000 - $ 3,000 4. Repair deteriorate asphalt road or remove and grass along top of embankment and fill sink hole. $5,000 – $15,000 Subtotal $9,500 - $25,000

Remedial Modification Recommendations 1. Mobilize / Demobilize $5,000 - $ 7,000 2. Repair/reconstruct mortared and dry laid stone walls $5,000 - $15,000 3. Repair leakage downstream face and at training wall $5,000 - $ 7,500 4. Repair deteriorated concrete on spillway and abutments $15,000 - $30,000 5. Install walkway over the spillway $35,000 - $50,000 19 Massabesic Lake Dam Date of Inspection: September 20, 2016 6. Revise flashboards to be collapsible $15,000 - $25,000

Subtotal $80,000 - $134,500

Engineering & Design $20,000 - $35,000 Permitting $ 5,000 - $15,000 Construction Administration $10,000 - $20,000

40%Contingency $55,400 - $97,400

RECOMMENDATIONS TOTAL $228,900 - $410,900

20 Massabesic Lake Dam Date of Inspection: September 20, 2016 FIGURES Massabesic Lake Dam Source:

USGS topo obtained from ESRI Map developed by Wright-Pierce GIS Dept ¥

Dam Site Location Latitude: 42.963 Longitude: -71.3955

0 2,000 4,000 Feet

Massabesic Lake Dam NH00103

Maine Vermont Manchester, New Hampshire New Hampshire (! !( Locus Plan PROJ NO: DATE: 13549A 9/30/2016 Massachusetts FIGURE:

ConnecticutRhode Island 1 CLM W:\GIS_Development\Projects\NH\Manchester\13549_DamEval\MXDs\Fig1_LocationMap_8x11.mxd Source:

All base mapping data obtained from NH GRANIT Map developed by Wright-Pierce GIS Dept ¥

Massabesic Lake

Dam Site Location Latitude: 42.963 Longitude: -71.3955

0 1,000 2,000 Feet

Massabesic Lake Dam NH00103

Maine Manchester, New Hampshire Vermont !( New Hampshire Aerial Plan !( PROJ NO: DATE: 13549A 9/30/2016 FIGURE: Massachusetts

ConnecticutRhode Island 2 CLM W:\GIS_Development\Projects\NH\Manchester\13549_DamEval\MXDs\Fig2_AerialMap_8x11.mxd ¥

Drainage Area 46.6 square miles

Dam Site Location Latitude: 42.963 Longitude: -71.3955

Massabesic Lake Dam

(! NH00103 Maine Manchester, New Hampshire Vermont New Hampshire Drainage Area New York (! PROJ NO: DATE: 13549A 9/30/2016 FIGURE: Massachusetts Sources: Esri, DeLorme, NAVTEQ, USGS, Connecticut Rhode Island NRCAN, METI, iPC, TomTom 3 CLM W:\GIS_Development\Projects\NH\Manchester\13549_DamEval\MXDs\Fig3_DrainageArea_8x11.mxd ¥

Dam Site Location Latitude: 42.963 Longitude: -71.3955

Source: USGS - ESRI Basemap Region and State Inset maps: ArcGIS Data Content

Massabesic Lake Dam (! NH00103 Maine Manchester, New Hampshire Vermont New Hampshire Downstream Area New York (! PROJ NO: DATE: 13549A 9/30/2016 FIGURE: Massachusetts Sources: Esri, DeLorme, NAVTEQ, USGS, Rhode Island Connecticut NRCAN, METI, iPC, TomTom 4 CLM W:\GIS_Development\Projects\NH\Manchester\13549_DamEval\MXDs\Fig4_DownstreamArea_8x11.mxd

Appendix A

APPENDIX A Photographs Massabesic Lake Dam

22 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo #1 - Overview of Dam from Upstream

Photo #2 - Overview of Dam from Downstream

23 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo #3 - Overview of Upstream Face from Right Embankment

Photo #4 - Overview of Upstream Face from Left Embankment

24 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo # 5 Overview Upstream of Spillway Crest

Photo #6 – Overview Canal Outlet

25 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo #7 – Upstream - Rodney Hunt Sluice Gate Operator Stem

Photo #8 – Downstream Outlet Pipe

26 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo #9 - Overview Upstream of Right Abutment/Embankment

Photo #10 - Overview Upstream of Left Abutment/Embankment

27 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo #11 - Overview Upstream

Photo #12 - Overview of Downstream Face from Left Abutment/Embankment

28 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo # 13 - Overview of Downstream Face from Right Abutment/Embankment

Photo # 14 - Overview of Spillway Crest from downstream

29 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 15 – Overview Downstream

Photo 16 – Spillway looking from Right Abutment

30 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 17 – Spillway looking from Left Abutment

Photo 18 – Downstream Right Abutment/Training Wall

31 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 19 – Downstream Left Abutment/Training Wall

Photo 20 – Flashboards (Fixed)

32 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 21 - Typical Stone Embankment (Right)

Photo 22 – Left Abutment

33 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 23 – Left Abutment Damaged Fence

Photo 24 – Downstream Right Embankment 34 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 25 – Top of Road/Right Embankment Looking Southwest

Photo 26 – Top of Road/Left Embankment Looking Northeast

35 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 27 – Downstream Left Embankment

Photo 28 – Canal looking towards Gate House

36 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 29 – Canal Ave looking toward Canal Gate Chamber (Lower End)

Photo 30 – Canal Entrance (Upper End)

37 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 31 –Canal Gate Chamber (Lower End)

Photo 32 – Canal looking back to Dam (Upper End)

38 Massabesic Lake Dam Date of Inspection: September 20, 2016 Photo 33 – Overview Upstream Coffer Dam Left Embankment

39 Massabesic Lake Dam Date of Inspection: September 20, 2016

Appendix B

APPENDIX B Inspection Checklist Massabesic Lake Dam

40 Massabesic Lake Dam Date of Inspection: September 20, 2016

Appendix C

APPENDIX C Historical Illustrations Massabesic Lake Dam

41 Massabesic Lake Dam Date of Inspection: September 20, 2016 42 Massabesic Lake Dam Date of Inspection: September 20, 2016 43 Massabesic Lake Dam Date of Inspection: September 20, 2016 44 Massabesic Lake Dam Date of Inspection: September 20, 2016 45 Massabesic Lake Dam Date of Inspection: September 20, 2016 46 Massabesic Lake Dam Date of Inspection: September 20, 2016 47 Massabesic Lake Dam Date of Inspection: September 20, 2016 48 Massabesic Lake Dam Date of Inspection: September 20, 2016

Appendix D

APPENDIX D Existing Drawings Massabesic Lake Dam

49 Massabesic Lake Dam Date of Inspection: September 20, 2016 EXISTING DRAWINGS

The following is a list of Drawings that were located during the file review, or were referenced in previous reports.

1. Mill Pond Dam, Manchester NH Waterworks, New Gate & Outlet Works, November 1945

2. Repair Plan for Massabesic Lake Main Dam, City of Manchester, NH, Manchester Waterworks by Hoyle, Tanner & Associates Inc., September 1995

50 Massabesic Lake Dam Date of Inspection: September 20, 2016

Appendix E

APPENDIX E Previous Reports and References Massabesic Lake Dam

51 Massabesic Lake Dam Date of Inspection: September 20, 2016 PREVIOUS REPORTS AND REFERENCES

The following is a list of reports that were located during the file review, or were referenced in previous reports.

1. “Annual Report, City of Manchester”1873, Engineers Report for the Massabesic Dam Construction Pages 61 to 66

2. “Manchester A Brief Record of Its Past and A Picture of Its Present”, John B. Clark, 1875, Illustrations of Manchester Water-Works; Pumping Station, Location of the Dam, Races, etc., Details of Penstock, Details of Dam, Section of Pumping Station and Pumps, Plan of Pumping Station and Pumps and Details of Reservoir.

3. J. T. Fanning, “A Practical Treatise on Water-Supply Engineering: Relating to the Hydrology, Hydrodynamics, and Practical Construction of Water-Works, in North American”, CE, New York, D Van Nostrand, Publisher, 1877

4. “Reports on the Water-Power of the United States, Part II”, Department of Interior, Census Office, 1887, Pages 118 to 122, Pumping by Water-Power Manchester, New Hampshire

5. “Engineering News”, Volume 75, Number 14, April 6, 1916, Pages 642 to 644, Modernizing the Manchester Water-Works.

6. “Massabesic Lake Dam, NH 00103, Phase I Inspection Report National Dam Inspection Program”, Department of the Army New England Division, Corps of Engineers, Waltham, MA 02154, Dated August 1978

7. New Hampshire Department of Environmental Services Letter of Deficiency Dated August 23, 2001

8. New Hampshire Department of Environmental Services Letter of Deficiency Dated August 18, 2008

9. New Hampshire Department of Environmental Services Letter of Deficiency Dated February 8, 2010

10. Underwater Solutions Inc., Report Main Dam Sluice Gate Control Rod Installation at Mill Pond, November 4, 2010

The following references were utilized during the preparation of this report and the development of the recommendations presented herein.

1. New Hampshire Code of Administrative Rules, Parts ENV-WR 100 to 700.

2. "ER 1110-2-106-Recommended Guidelines for Safety Inspection of Dams", Department of the Army, September 26, 1979

3. "Design of Small Dams", United States Department of the Interior Bureaus of Reclamation, 1987

52 Massabesic Lake Dam Date of Inspection: September 20, 2016

Appendix F

APPENDIX F Definitions Massabesic Lake Dam

53 Massabesic Lake Dam Date of Inspection: September 20, 2016 COMMON DAM SAFETY DEFINITIONS

For a comprehensive list of dam engineering terminology and definitions refer to New Hampshire Code of Administrative Rules, Parts ENV-WR 100 to 700 or other reference published by FERC, Dept. of the Interior Bureau of Reclamation, or FEMA.

Hazard Classification

High Hazard (Class C) – A dam that has a high hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in probable loss of human life as a result of: · Water levels and velocities causing the structural failure of a foundation of a habitable residential structure or commercial or industrial structure, which is occupied under normal conditions. · Water levels rising above the first floor elevation of a habitable residential structure or a commercial or industrial structure, which is occupied under normal conditions when the rise due to dam failure is greater than one foot. · Structural damage to an interstate highway, which could render the roadway impassable or otherwise interrupt public safety services. · The release of a quantity and concentration of material, which qualify as “hazardous waste” as defined by RSA 147-A:2 VII. · Any other circumstance that would more likely than not cause one or more deaths.

Significant Hazard (Class B) – A dam that has a significant hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in any of the following: · No probable loss of lives. · Major economic loss to structures or property. · Structural damage to a Class I or Class II road that could render the road impassable or otherwise interrupt public safety services. · Major environmental or public health losses, including one or more of the following: · Damage to a public water system, as defined by RSA 485:1-a, XV, which will take longer than 48 hours to repair. · The release of liquid industrial, agricultural, or commercial wastes, septage, sewage, or contaminated sediments if the storage capacity is 2 acre-feet or more. · Damage to an environmentally-sensitive site that does not meet the definition of reversible environmental losses.

Low Hazard (Class A) – A dam that has a low hazard potential because it is in a location and of a size that failure or misoperation of the dam would result in any of the following: · No possible loss of life. · Low economic loss to structures or property. · Structural damage to a town or city road or private road accessing property other than the dam owner’s that could render the road impassable or otherwise interrupt public safety services. · The release of liquid industrial, agricultural, or commercial wastes, septage, or contaminated sediment if the storage capacity is less than two-acre-feet and is located more than 250 feet from a water body or water course. · Reversible environmental losses to environmentally-sensitive sites.

54 Massabesic Lake Dam Date of Inspection: September 20, 2016 Non Menace (Class AA) – A dam that is not a menace because it is in a location and of a size that failure or misoperation of the dam would not result in probable loss of life or loss to property, provided the dam is: · Less than six feet in height if it has a storage capacity greater than 50 acre-feet; or · Less than 25 feet in height if it has a storage capacity of 15 to 50 acre-feet.

Size Classification (US Army Corps of Engineers 1979)

Large – structure with a height greater than 100 feet or a storage capacity greater than 50,000 acre-feet.

Intermediate – structure with a height between 40 and 100 feet or a storage capacity of 1,000 to 50,000 acre-feet.

Small – structure with a height between 25 and 40 feet and a storage capacity of 50 to 1000 acre- feet.

Orientation

Upstream – Shall mean the side of the dam that borders the impoundment.

Downstream – Shall mean the high side of the dam, the side opposite the upstream side.

Right – Shall mean the area to the right when looking in the downstream direction.

Left – Shall mean the area to the left when looking in the downstream direction.

Dam Components

Dam – Shall mean any artificial barrier, including appurtenant works, which impounds or diverts water.

Embankment – Shall mean the fill material, usually earth or rock, placed with sloping sides, such that it forms a permanent barrier that impounds water.

Crest – Shall mean the top of the dam, usually provides a road or path across the dam.

Abutment – Shall mean that part of a valley side against which a dam is constructed (the area that borders either end of a dam). “Right” and “Left” designations are from the perspective of someone looking downstream towards the dam. An artificial abutment is sometimes constructed as a concrete gravity section, to take the thrust of an arch dam where there is no suitable natural abutment.

Foundation - The natural soil or rock material upon which a dam is built.

Appurtenant Works – Shall mean structures, either in dams or separate therefrom, including but not be limited to, spillways; reservoirs and their rims; low-level outlet works; and water conduits including tunnels, pipelines, or penstocks, either through the dams or their abutments.

55 Massabesic Lake Dam Date of Inspection: September 20, 2016 Low Level Outlet - An opening at a low level in a reservoir generally used for emptying the reservoir or scouring sediment and sometimes for irrigation.

Outlet Works - The conduits and valves which allow for the discharge of water form the impoundment.

Flashboards - A length of timber, concrete or steel placed on the crest of a spillway to raise the retention water level but that may be quickly removed in the event of a flood either by a tripping device or by a deliberately designed failure of one or more flashboards or its supports.

Spillway – Shall mean a structure over or through which water flows are discharged. If the flow is controlled by gates or boards, it is a controlled spillway; if the fixed elevation of the spillway crest controls the level of the impoundment, it is an uncontrolled spillway.

General

EAP – Emergency Action Plan – Shall mean a predetermined (and properly documented) plan of action to be taken to reduce the potential for property damage and/or loss of life in an area affected by an impending dam failure.

O&M Manual – Operations and Maintenance Manual; Document identifying routine maintenance and operational procedures under normal and storm conditions.

Normal Pool – Shall mean the elevation of the impoundment during normal operating conditions.

Acre-foot – Shall mean a unit of volumetric measure that would cover one acre to a depth of one foot. It is equal to 43,560 cubic feet. One million U.S. gallons = 3.068 acre feet.

Height of Dam (Structural Height) – Shall mean the vertical distance from the lowest portion of the natural ground, including any stream channel, along the downstream toe of the dam to the lowest point on the crest of the dam.

Hydraulic Height – means the height to which water rises behind a dam and the difference between the lowest point in the original streambed at the axis of the dam and the maximum controllable water surface.

Maximum Water Storage Elevation – means the maximum elevation of water surface which can be contained by the dam without overtopping the embankment section.

Spillway Design Flood (SDF) – Shall mean the flood used in the design of a dam and its appurtenant works particularly for sizing the spillway and outlet works, and for determining maximum temporary storage and height of dam requirements.

Maximum Storage Capacity – The volume of water contained in the impoundment at maximum water storage elevation.

Normal Storage Capacity – The volume of water contained in the impoundment at normal water storage elevation.

56 Massabesic Lake Dam Date of Inspection: September 20, 2016 Freeboard - In general, the vertical distance between a stated water surface and the top of a dam. Sometimes defined as the vertical distance between the normal water level and the top of dam.

Impoundment - The reservoir, pond or other body of water retained by a dam.

Tailwater Level - The level of water in the discharge channel immediately downstream of the dam.

Condition Rating

Unsafe – Through file research and after a visual inspection it has been determined that a deficiency is recognized that requires immediate or emergency action. Major structural*, operational, and maintenance deficiencies exist under normal operating conditions.

Poor – Through file research and after visual inspection it has been determined that deficiencies are recognized that require engineering analysis and/or remedial action. A POOR condition is used when uncertainties exist as to critical analysis parameters, which identify a potential dam safety deficiency. Further investigations and studies are necessary. Significant structural*, operation and maintenance deficiencies are clearly recognized for normal loading conditions.

Fair – Through file research and after a visual inspection, there are no critical deficiencies with the dam that would require engineering analysis with the following exception: the engineer may recommend that a hydrologic and hydraulic analysis be conducted due to the lack of adequate freeboard and/or the lack of spillway capacity documentation. Significant operational and maintenance deficiencies, no structural deficiencies. Potential deficiencies exist under unusual loading conditions that may realistically occur. Can be used when uncertainties exist as to critical parameters.

Satisfactory – Through file research and after a visual inspection, minor operational and maintenance deficiencies. Infrequent hydrologic events would probably result in deficiencies.

Good – Through file research and after a visual inspection, no existing or potential deficiencies are recognized. Safe performance is expected under all loading including SDF.

* Structural deficiencies include but are not limited to the following:

· Excessive uncontrolled seepage (e.g., upwelling of water, evidence of fines movement, flowing water, erosion, etc.) · Missing riprap with resulting erosion of slope · Sinkholes, particularly behind retaining walls and above outlet pipes, possibly indicating loss of soil due to piping, rather than animal burrows · Excessive vegetation and tree growth, particularly if it obscures features of the dam and the dam cannot be fully inspected · Deterioration of concrete structures (e.g., exposed rebar, tilted walls, large cracks with or without seepage, excessive spalling, etc.) · Inoperable outlets (gates and valves that have not been operated for many years or are broken)

57 Massabesic Lake Dam Date of Inspection: September 20, 2016