emergency response and rehabilitation of spillway damage

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21st Century Dam Design —

Advances and Adaptations

31st Annual USSD Conference

San Diego, California, April 11-15, 2011

On the CoverArtist's rendition of San Vicente Dam after completion of the dam raise project to increase local storage and provide

a more flexible conveyance system for use during emergencies such as earthquakes that could curtail the region’s

imported water supplies. The existing 220-foot-high dam, owned by the City of San Diego, will be raised by 117

feet to increase reservoir storage capacity by 152,000 acre-feet. The project will be the tallest dam raise in the

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Emergency Response and Rehabilitation 811

EMERGENCY RESPONSE AND REHABILITATION OF SPILLWAY DAMAGE CAUSED BY A MOTHER’S DAY STORM

Stephen L. Whiteside, P.E.1

Tyler C. Dunn, P.E.2 Aaron J. Rubin, E. I. T.3

Richard Dawe4

ABSTRACT

During Mother’s Day weekend in 2006, a 100-year, 48-hour storm dropped more than 11 inches of rain in some regions of Massachusetts, including Walden Pond located in Saugus and Lynn. The west end of the pond in Saugus is impounded by the Walden Pond Outlet Dam, an earthen embankment with a concrete core wall, that is classified as a large, high-hazard potential dam. During the storm, flow into the spillway rose rapidly to a maximum depth of 1.5 feet above the spillway crest which resulted in erosion and damage to the downstream discharge channel. An emergency watch was organized to monitor the erosion occurring at the left training wall and an evacuation plan was established. A Phase I inspection of the dam, performed by CDM in August 2006, concluded that the overall condition of the dam was poor due to the damage and erosion of the spillway. The Massachusetts Office of Dam Safety (ODS) reviewed the Phase I report and ordered the dam owner to perform a Phase II investigation of the dam. The Phase II inspection/investigation prepared by CDM in 2008 evaluated the spillway capacity and embankment slope stability, and provided conceptual remediation options to bring the dam into compliance. CDM prepared the final design contract documents for rehabilitation of the spillway and construction was performed between August and December 2009. This paper will present the extent of the storm’s damage, emergency response, and the constructed design features to ensure repeat storm damage does not occur.

INTRODUCTION The water supply system of the city of Lynn, Massachusetts was established in 1870 when Breeds Pond was purchased as the first source of water supply. Birch Pond was added as a source to the system during 1873 when Beaver Brook was dammed to help supply water to Lynn. Walden Pond was created in 1890 by constructing a dam across Penny Brook and combining it with Glen Lewis Pond. Walden Pond is part of a series of interconnected reservoirs that provide the local water supply to Lynn. Construction of Hawkes Pond Dam was completed during 1895 creating Hawkes Pond reservoir. The 1 Vice President, CDM, 5400 Glenwood Avenue Suite 300, Raleigh, NC 27612 [email protected] 2 Senior Geotechnical Engineer, CDM, 50 Hampshire Street, Cambridge, MA 02139 [email protected] 3 Geotechnical Engineer, CDM, 50 Hampshire Street, Cambridge, MA 02139 [email protected] 4 Superintendent, Lynn Water & Sewer Commission, 390 Parkland Avenue, Lynn, MA 01905 [email protected]

812 21st Century Dam Design — Advances and Adaptations

Saugus River diversion conduit was completed in 1898, connecting the Saugus River to Hawkes Pond. During 1918, the connection between the Ipswich River and Lynn’s reservoir system was established, completing the existing water supply system. The interconnected reservoirs include Breeds Pond, Birch Pond, Walden Pond, and Hawkes Pond. The series of four interconnected reservoirs, primarily supplied by the Saugus and Ipswich rivers, provide about 11 million gallons of water per day to Lynn. Lynn Water and Sewer Commission (LWSC) manages the water system and maintains the dams and dikes that impound the reservoirs. At capacity, the water system holds about 4.2 billion gallons of water.

WALDEN POND OUTLET DAM

The Walden Pond Outlet Dam (NID MA00246) is located in the town of Saugus, Massachusetts. Walden Pond is located just east of Route 1 and west of Route 107 and is situated within the middle portion of Lynn Woods Reservation, a municipal forest public park. Walden Pond has a capacity of about 1.9 million gallons and a water depth of 39.3 feet. The impoundment system includes the large Outlet Dam at the west end of the pond and the significantly smaller East End Dam located at the extreme eastern limit of the pond in Lynn. The watershed draining into Walden Pond is shown on Figure 1. The watershed drainage area is 1.62 square miles, including the reservoir normal pool (spillway crest) area of 233 acres that represents approximately 22 percent of the watershed area.

Figure 1. Location of Walden Pond

Figure 2. Walden Pond Outlet Dam Aerial


Walden Pond Outlet Dam is a 2,190-foot-long earthen embankment with a concrete core wall and sheeting extending below the core wall. An aerial view of the dam is shown on Figure 2. It was built in 1890 and raised in 1905 when the East End Dam was constructed. The embankment is continuous, but is configured as three straight sections with two bends. The bend at the left portion of the embankment forms an obtuse angle of about 135 degrees facing upstream. The bend at the right portion of the embankment forms a similar obtuse angle of 135 degrees facing downstream. The embankment crest is about 45 feet wide and the entire surface, up to the spillway, is covered with crushed stone over a geotextile fabric. The crest is used as a vehicle access road by LWSC. The upstream slope of the embankment has a 2H:1V slope and is protected by placed stone riprap. The downstream slope has a 1.75H:1V slope and is covered with grass and brush vegetation. Gabion drainage blankets are placed at three locations near the lower portion of the downstream slope for seepage control (Figure 3). The spillway is located at the extreme right end of the embankment and discharges into a 250-foot-long curved discharge channel running along the downstream toe of the embankment. The dam’s spillway is a broad-crested ungated weir, with a crest elevation approximately four feet below the crest of the dam. The discharge channel was covered with riprap over bedrock and naturally deposited soils. The left side of the discharge channel transitions from a stone masonry training wall to a line of large boulders and bedrock outcrops at the toe of the downstream slope of the embankment. The right side of the discharge channel is excavated into natural soils, boulders and bedrock. Water flow through the spillway discharges into some wetland areas beyond the toe of the embankment that link to Hawkes Brook and then to the Saugus River. Walden Pond Outlet Dam has a maximum structural height of 43.3 feet and a maximum storage capacity of 6,900 acre-feet. The Outlet Dam is classified as a large size structure and a high-hazard potential dam in accordance with Office of Dam Safety classification, under Commonwealth of Massachusetts dam safety rules and regulations stated in 302 CMR 10.00 as amended by Chapter 330 of the Acts of 2002. The area downstream of the dam is developed with local neighborhood streets, residential homes, commercial businesses, and the well-traveled Route 1. A dam inspection sketch is shown on Figure 4.

In accordance with the dam safety regulations, the spillway design flood (SDF) for the Walden Pond Outlet Dam is the ½ Probable Maximum Flood (½ PMF). The SDF inflow for this event is 4,900 cubic feet per second (cfs), and the corresponding routed SDF outflow is 458 cfs. The spillway capacity with a water surface at the dam crest is 960 cfs, or 210 percent of the routed SDF outflow. The existing spillway has adequate capacity to pass the SDF.

Figure 3. Downstream Slope


A concrete intake structure (former gatehouse) is located about 95 feet from the upstream crest of the dam. The former superstructure was removed as part of the recent rehabilitation work in 1996. Access to the gate house is currently only possible by boat, since the former footbridge connected to the crest has been removed. The intake structure has four multilevel intake screens. Two 36-inch-diameter water supply intake pipes originate at the intake structure. On the downstream side, both lines reduce to single 30-inch-diameter pipes that begin the transmission system that controls the discharge to

Figure 4. Inspection Field Sketch


Birch Pond. One of the 36-inch pipes also functions as a blow-off line that can discharge to a tributary to Hawkes Brook via a 24-inch-diameter low-level outlet from a tee off the 36-inch pipe.

STORM EVENT

Early spring 2006 in Massachusetts was exceptionally dry. The month of March 2006 was the second driest on record and precipitation in April was only 50 percent of normal. Brush fire danger had been running high until the Mothers Day weekend. Mother's Day weekend 2006 was a time when all that changed in northeast Massachusetts and south central New Hampshire. Relentless rains began Friday evening and lasted through Monday morning. The 100-hour rain event was driven by a stationary area of low pressure south of Boston that tapped into deep tropical moisture over the Atlantic Ocean. Storm totals close to 12 inches were recorded at many locations in Essex County. This rainfall caused most rivers in northeastern Massachusetts to reach record-high and near-record-high flows. Rivers flowed over bridges, into streets and filled basements forcing road closures and emergency evacuations. Dams were overtopped in some communities. In Ipswich, two of the three downtown bridges were weakened by the normally tranquil Ipswich River, leaving only one bridge to traverse town.

Route 1, a major conduit to Boston and Logan Airport, was closed for several days due to significant rise of the Saugus River. Serious flooding also occurred along the Merrimack River as docks from marinas and other water-born debris piled up at the mouth of the

river. Although this rainstorm occurred after 3 dry months preceding May, 3 to 6 inches of rain had already fallen in early May, setting the stage for serious flooding.

The major storm actually started on Friday, May 12 and ended into the week ending during the morning hours of Wednesday, May 17th. The storm dumped up to a foot of rain in many areas in northeastern Massachusetts and southern New Hampshire (Figure 6). Adding to the problem were over-

Figure 5. Route 1 in Saugus, MA

Figure 6. Saugus River Overflow at Elm Street Bridge


flowing rivers and the prediction of more rain over the next week. The Mother's Day storm contributed to historic rainfall totals for the month of May and stream flows for the record books. The governor of Massachusetts declared a state of emergency. The governor described the flooding as "almost Biblical" and said "We're sort of making jokes about Noah and taking two of each kind of animal because we haven't ever seen rain like this.” The Federal Emergency Management Agency (FEMA) toured the state and a federal disaster was declared on May 25, 2006 with later amendments, ensuring financial relief for the counties of Essex, Middlesex, and Suffolk (Figure 7).

According to U. S. Geological Survey (USGS) flow measurements, the Merrimac River in Lowell was at its highest flood stage since the hurricane of 1938 and the third highest ever measured. Over a 2-day period in Saugus, 5.5 inches fell on May 13 and 5.8 inches fell on May 14, for a total of 11.3 inches. This storm was categorized a 100-year 48-hour storm. The National Weather Service predicted an additional 1 to 6 inches by Wednesday, pushing rain totals near records set in 1936 and 1938. About 17 inches of rain fell in the month of May which was indicative of the wettest month on record for some Massachusetts locations (Figure 8).

Figure 7. FEMA Disaster Declaration


EMERGENCY RESPONSE AND SUMMARY OF EVENTS

On Sunday, May 14, 2006, LWSC personnel noted the reservoir level in Walden Pond began to overtop the spillway at Walden Pond Outlet Dam. The spillway appeared to be functioning as intended with no obvious significant signs of erosion (Figures 9 and 10).

Early in the morning on Monday, May 15, LWSC personnel responded to a call from the town of Saugus and observed that the spillway channel at Walden Pond Dam began to

Figure 9. Approach Spillway Figure 10. Spillway Weir

Figure 8. Storm Depth – Duration Curve


show signs of significant erosion. The erosion was occurring near the center of the spillway and was encroaching toward the left training wall and the toe of the dam. Upon

observing these conditions, LWSC, acting through the Massachusetts Emergency Management Agency (MEMA), notified the Office of Dam Safety.

Later that morning, a meeting was organized at the dam, attended by CDM, representatives of LWSC, a consultant representing the ODS, and several officials from the town of Saugus including the fire chief and the director of Saugus Emergency Management Agency. The representatives remained at the site during the day and into the evening. Observations made and the sequence of events that occurred are described below.

The elevated reservoir level led to high flows through the spillway, resulting in erosion in the downstream channel that was progressively moving towards the left training wall and the toe of the dam (Figures 11 and 12). The height of the flow over the spillway was about 1.5 feet at about 2:00 PM.

Since the erosion was progressively moving towards the left training wall, it was determined by ODS and CDM that there was the possibility that it could be undermined and possibly be washed out. Without the training wall, flow through the spillway could erode the dam’s embankment soils and possibly result in failure of the dam. Based on this potential condition, it was agreed that an emergency condition existed and appropriate actions were necessary.

Figure 13. Preparation for Washout

Figure 12. Left Training Wall Figure 11. Discharge Channel to Wetland


As recommended by ODS and CDM, LWSC mobilized a contractor with a tracked excavator and several 3- to 5–foot-diameter boulders to the dam to be able to quickly replace the training wall if it were washed out (Figure 13). LWSC personnel and the contractor remained onsite overnight to monitor the condition of the spillway, prepared to perform emergency repairs if needed.

An emergency action plan was in early stages of development, but had not been completed prior to the storm event. Therefore, an evacuation plan needed to be developed. Saugus officials mobilized an emergency command center at the dam, developed a notification plan for the downstream residents and established a communication chain to be used if an emergency situation developed. ODS contacted the U. S. Army Corps of Engineers (USACE) who provided the estimated downstream flood elevation if the dam were to fail. The ODS consultant recommended that the low-level outlet be opened. The ODS consultant roughly identified the inundation area using available topographic plans and the flood elevation provided by the USACE. The inundation map plan was given to a representative of the Saugus Emergency Management Agency to be used in their emergency response planning efforts.

Full-time monitoring of the spillway continued through the night of May 16 and then on a part-time basis through May 18. By 11:00 AM on May 18, the flow in the spillway dropped to about 4 inches over the spillway crest.

Since the flow in the spillway channel had subsided, a partial view of the left training wall was possible (Figure 14). The downstream portion of the left training wall appeared to be founded on soil over bedrock and therefore remained susceptible to erosion.

A second meeting was held at the dam on May 18. That meeting was attended by CDM, representatives of LWSC, the consultant and director of the ODS, chief of the Saugus Fire Department, and a representative of the Massachusetts Highway Department (MassHighway). ODS directed the low-level outlet be kept open until the flow through the spillway stopped because the left training wall was founded on soils that remained susceptible to erosion.

LWSC had been in daily contact with ODS since May 15 and was authorized to throttle back the low-level outlet starting on Saturday, May 20. LWSC had also pumped approximately 20 million gallons per day from Walden Pond to Breeds Pond between Saturday, May 20 and Monday, May 22. On May 23, a site visit was performed by CDM and LWSC personnel to assess the condition of spillway. Upon arrival to the dam, the reservoir level was 15 inches below the crest of the spillway and the low-level outlet was approximately half closed.

Figure 14. Undermining of Left Training Wall


DESCRIPTION OF SPILLWAY CONDITION FOLLOWING THE STORM A preliminary assessment of the spillway and portions of the dam was made by CDM engineers during the May 23 site visit. Since the flow through the spillway had stopped, CDM engineers were able to enter the downstream spillway channel and make the following observations:

The riprap in the downstream channel had been eroded and scoured. The riprap had been removed down to bedrock within the upper 40 feet of the downstream channel. The depth of the erosion ranged from about 1 foot near the spillway crest to about 4 feet at a distance of about 40 feet downstream of the crest.

The material within the downstream spillway channel appeared to consist of about a 1-foot-thick layer of 6- to 8–inch-diameter riprap. This layer was over 1 to 2 feet of a riprap/fill soil matrix over naturally deposited glacial till soils and then bedrock. The bedrock surface near the left training wall was sloping steeply downstream and slightly towards the left training wall. The sloping of the bedrock appeared to have directed the flow in the spillway towards the left training wall, and was a contributing factor in the erosion of the spillway channel.

The downstream side of the spillway had a mortared stone training wall on the left side and an excavated soil/boulder lined slope along the right side (Figure 17). A few of the top cap stones of the left training wall appeared to be slightly dislodged and moved slightly outward towards the spillway channel.

The riprap material at the base of the left training wall in the downstream channel had been completely removed to an approximate distance of about 40 feet from the spillway crest. The first 25 feet of the wall beginning at the spillway crest appeared to be founded on bedrock (Figure 17). The remaining 15 feet of the wall appeared to be founded on naturally deposited glacial till soil that ranged in thickness from a few inches to about 1.5 feet.

Figure 15. Two Feet of Erosion in Discharge Channel

Figure 16. Undermined Segment of Left Training Wall


A 2-foot-long section of the downstream left training wall had been undermined. The undermined section was up to 7 inches in height and extended about 25 inches inward beneath the lowest stone course of the wall.

The riprap within the spillway channel had been transported a significant distance down the channel and into the wetland area at the toe of the dam.

The toe of the dam below the training wall had little protection against erosion or scour. However, no significant erosion was observed below the left training wall along the toe of the dam.

The concrete weir at the crest of the spillway appeared to be intact and did not appear to have been damaged. The approach area of the spillway contained some brush and debris. The upstream

training wall consisted of mortared stone and appeared to be in relatively good condition.

Phase I Inspection and Phase II Investigation

A Phase I inspection was performed in August 2006 following an order by ODS. Following review of that inspection report by ODS, an order to conduct a Phase II Investigation was issued to LWSC by ODS in accordance with the Certificate of Non-Compliance and Dam Safety Order, dated mid-November 2007. The basis for the order was developed as a result of the observations during the August 2006 Phase I inspection, and reported in the Phase I Inspection Report for Walden Pond Outlet Dam and East End Dam performed by CDM. Although most of the dam components of the Outlet Dam were judged to be in fair condition, the overall condition of the dam was rated as “poor” based on the severe erosion in front of the left training wall and on the discharge channel of the spillway that had occurred during flooding events.

CDM was retained by the LWSC to perform the engineering services required to comply with the order. CDM submitted a 6-month follow-up inspection report as required by the Order. CDM also completed the updated detailed Phase I inspection in June 2008 required for the Phase II Investigation. These inspections found the condition of the dam to be substantially unchanged compared to that reported in the August 2006 Phase I inspection report. To evaluate the dam and develop concept designs, the Phase II investigation also included wetland delineation and a topographic survey, review of required permits for construction, a subsurface investigation program, slope stability and seepage analyses, and hydrologic and hydraulic analyses for the spillway.

CDM performed the Phase II investigation and developed design concept details for repair of the spillway. In summary, the existing left and right stone masonry training walls of the approach channel were to be restored as required up to a point just

Figure 17. Post-Storm View of Erosion of Discharge Channel


downstream of the existing weir. The remainder of the existing left stone masonry training wall downstream of the weir was to be removed and replaced with a new structural concrete cantilever retaining wall. The new retaining wall matched the similar alignment of the existing wall, but extended a further distance down the left side of the discharge channel. The existing discharge channel riprap floor downstream of the existing weir was replaced with structural concrete for a short distance. The discharge channel downstream of the concrete floor was constructed of grouted riprap. The toe of the downstream slope of the dam beyond the end of the new left training wall was faced with grouted riprap, to protect the toe from potential erosion. The right side of the discharge channel was sloped and protected with grouted riprap.

As part of the Phase II work, CDM performed a subsurface investigation and performed seepage and stability analyses for the existing embankment in accordance with the requirements in 302 CMR 10.00 (Figures 18 and 19). Based on these analyses and the steepness of the downstream slope, the existing downstream slope did not meet the minimum factor of safety for normal pool and maximum pool steady-state conditions. However, the critical failure surfaces were shallow and restricted by the core wall in the dam. Additional stability analyses were performed to evaluate the potential impact of a shallow slope failure on the overall stability of the dam. The results of the analyses indicated that a shallow failure in

Figure 18. Subsurface Investigation

Figure 19. Stability Analysis Results


the downstream slope should not impact the overall stability of the dam. CDM recommended that a formal periodic monitoring and inspection program be established to monitor phreatic surface levels and make periodic visual observations of the dam. If shallow failures were to occur, they could be detected and repaired. There have been no signs of slope stability problems, and the piezometer levels indicate that the concrete core wall is effective in reducing seepage.

DESIGN IMPLEMENTATION TO ACHIEVE COMPLIANCE

CDM designed the recommended repairs and rehabilitation of the spillway. Application for the required permit under MGL Chapter 253 and the Dam Safety Regulations (302 CMR 10.00) was submitted to the ODS in February 2009. The permit application included a final design report and the construction drawings and specifications. The proposed repairs were intended to bring the dam into compliance with the Dam Safety Order and improve the overall rating of the dam. The existing spillway was intended to be repaired to generally replicate the look and dimensions of the structure as it existed prior to being damaged by the May 2006 flood, but would be strengthened to reduce the potential for a future recurrence of the damage (Figures 20 through 22).

Figure 20. Contract Drawing of Plan for Repairs


Inspection of the existing spillway structure and discharge channel by CDM structural and geotechnical engineers established that the spillway is constructed and founded on a sound, solid bedrock outcrop, and that this rock lies close to the surface of much of the discharge channel.

Figure 21. One Design Section of Spillway

Figure 22. Typical Detail of Spillway Design Features


The spillway was strengthened against being damaged again in the future by adding a reinforced concrete training wall to the embankment (left) side of the channel and a grouted riprap slope to the right side of the discharge channel (Figure 23). Repairs to the discharge channel also included design of a structural concrete slab as an extended weir anchored into the bedrock, and grouted riprap floor with natural boulders as energy dissipaters partially embedded in the lower portion of the channel.

The hydrologic and hydraulic calculations used to determine the spillway design flood discharge, spillway capacity, SDF freeboard, and wave action demonstrated that the spillway geometry provides an adequate outlet capacity for the dam. The design included a wave analysis showing that the stillwater freeboard during the spillway design flood (SDF) will be 1.1 feet for a starting reservoir level at the normal (spillway crest, El. 90.9 feet) pool level. Waves for 50- and 100-year wind speeds are predicted to be above the embankment crest elevation for the peak SDF reservoir level. However, due to the 45-foot-wide crest, the waves are not expected to impact the stability of the dam. Also, since the operating policy for the reservoir is to maintain a maximum reservoir level not less than 1 foot below the spillway crest, the available freeboard would be greater. The reservoir would not need to be drained to construct the proposed spillway.

REHABILITATION AND CONSTRUCTION OF SPILLWAY

Bidding

Following the advertisement for bids, eight bids were received at LWSC. The bids ranged from a low bid of about $507,000 to a high bid of $700,500. CDM’s construction cost estimate for the project was $675,000.

The three lowest bids were reviewed and evaluated by LWSC. Those bids were $574,773, $553,246, and $507,068. The lowest responsible and eligible bidder submitting the bid of $507,068 was awarded the contract following CDM’s recommendation. The final construction cost was the same as the bid.

Figure 23. Design Profile of Spillway and Discharge Channel


Construction Schedule

A summary of the key dates that were met to implement the construction are presented below. Construction photographs are shown on Figures 24 through 36.

Submit permit application to ODS February 2009 Submit Notice of Intent to Saugus Conservation Commission February 2009 SCC Board issued order of conditions March 2009 Obtain dam safety permit April 2009 Advertise for bids June 2009 Open bids June 2009 Start construction August 2009 Complete construction December 2009

Figure 25. Support of Excavation for Training Wall (9/9/09)

Figure 26. Concrete Fill Subgrade for Training Wall (9/11/09)

Figure 24. Installation of Soldier Piles (8/27/09)


Figure 27. Forms for Spillway Training Wall (9/22/09)

Figure 28. Concrete Spillway Training Wall (9/29/09)

Figure 29. Placement of Grout (10/1/09)

Figure 30. End of Grouted Riprap Discharge Channel (10/6/09)

Figure 31. Construction of Right Approach Training Wall (10/27/09)


THE PROJECT BEGINNING TO END

Figure 32. Overview of Discharge Channel (11/3/09)

Figure 33. New Concrete Spillway Weir (12/10/09)

Figure 34. Mother’s Day 2006

Figure 36. The End Result

Figure 35. Damage After Storm


SPILLWAY PERFORMANCE

The completed spillway was provided the opportunity for a test run at the beginning of April 2010 following heavy rainfall in March. Two 50-year storms struck the New England region in the middle and end of the month with record amounts of rainfall, causing flooding, evacuations and much damage. Massachusetts and two other states declared state emergencies. FEMA again declared a federal disaster for severe rain and flooding 4 years after the 2006 Mothers Day event. Rainfall amounts of about 10 inches and 6 inches for the respective storms occurred within 30 miles of the Massachusetts coast. The rain abated at the end of March but rivers continued to rise.

As some of the Lynn reservoirs reached beyond capacity near the end of March, rising water at Walden Pond began to flow through the spillway on March 31. CDM visited the site on Thursday April 1 and photographed the flow when the water level was 3.4 inches above the weir crest. A few of the photographs showing the flow event are presented on Figure 37.

Figure 37. Flow through Spillway


CONCLUSIONS This project demonstrated the success of responses to a significant storm event to mitigate the potential breaching of a dam. Although the intensity of the Mother’s Day 2006 storm resulted in discharge flows that caused serious erosion and damage to the spillway, the result of the response action by the dam owner in concert with emergency response officials and representatives of the state dam safety regulatory agency allowed assessment of the dam safety conditions and appropriate emergency response decisions to be made quickly. Subsequent observations and inspections of the damaged spillway and the dam embankment resulted in the rehabilitation design and construction to bring the dam into compliance with the required regulations.

REFERENCES Information describing the storm was summarized from various web-based links to news agencies such as Boston.com (Boston Globe), WBZ TV, USA Today, the Lynn Journal, and the Federal Emergency Management Agency (FEMA). Selected photographs displaying the flooding were selected from reader-contributed photographs presented in web-based links Boston.com and Saugus.net.

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