1. Geotechnical
Environmental
Water Resources
Ecological
•GEl Consultants
October 27,2010
Project 10426-0
The Friends ofthe
Upper Roberts Meadow Reservoir and Dam
P.O. Box 561
Leeds,MJ 01053
Dear Friends:
Re: Hazard Class Review
Upper Roberts Meadow Reservoir Dam
Northampton, Massachusetts
This letter presents the results of our investigation of the hazard potential classification assigned to
the Upper Roberts Meadow Reservoir Dam and evaluation of the feasibility of requesting a Hazard
Classification Change from the Massachusetts Office of Dam Safety (ODS).
Summary
We reviewed the studies performed by GZJ GeoEnvironmental, Inc. (GZJ) to estimate
downstream flooding from a breach of the Upper Roberts Meadow Reservoir Dam during both a
fair weather failure and a failure during a flood. The hazard rating for the dam is based on the
amount ofdamage expected downstream following a dam failure under either ofthese two
conditions, whichever is worse. The current hazard rating of"High Hazard Potential" appears to
be based on failure ofthe Lower Roberts Meadow Reservoir Dam and associated incremental
flooding caused by the failure ofthe Upper Roberts Meadow Reservoir Dam during a flood event
equal to the 500-year flood.
In our opinion, it might be possible to reduce the hazard rating to "Significant Hazard Potential" if
the following factors are taken into account:
1. The Upper reservoir has significantly less storage capacity due to siltation than assumed in
the GZJ analyses (19 acre-ft vs. 35 acre-ft) based on a recent bathymetric survey. This
means that in a dam failure scenario, less water would be released downstream.
2. The available mapping used by GZJ was based on 10-ft contour intervals (which may
have been all that was available at the time). Mapping with 5-ft contour intervals is now
available from the City ofNorthampton. Combined with the additional computation power
of the computer program HEC-MS and the use of GIS, use of the more detailed mapping
may show that more water can be stored between the Upper and Middle reservoirs,
attenuating the flood wave as it travels downstream and lessening the downstream impacts.
Given that the GZJ report indicated that the Lower Dam was only "slightly overtopped"
by a dam breach during the 500-year flood, only a small increase in the upstream storage
might be enough to show the overtopping is prevented.
www.geiconsultants.com GEl Consultants, Inc.
400 Unicorn Park Drive, Woburn, MA 01801
781.721.4000 fax: 781.721.4073

2. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
-2- October 27,2010
It is our opinion that we would not be able to show that the hazard classification should be "Low,"
because breach flows are likely to flood and potentially damage the adjacent secondary roads
(Chesterfield Road andlor Reservoir Road).
The Upper Roberts Meadow Reservoir Dam is in Poor condition and several of the deficiencies
will need to be addressed regardless ofthe hazard potential classification. If the dam is reclassified
to a Significant hazard potential dam, the spillway will still need to be enlarged to safely pass the
1~O-year flood or the right embankment and left dike will need to be raised or hardened to allow
flow over the top without washing out the embankment fill. However, the spillway enlargement or
embankment modifications will be significantly less expensive for a 1DO-year flood rather than for
a SOD-year flood. In addition, the stability analyses performed by GZA indicated that the spillway
was not stable for several required loading cases unless three-dimensional buttressing effects (due
to the dam's curved shape) were included. A more detailed three-dimensional evaluation might
show that the dam can meet stability criteria.
Background
The Upper Roberts Meadow Reservoir Dam (Upper Dam) is located in Leeds, Massachusetts, and
is a curved gravity masonry (granite block) dam built in 1883. The dam includes an earth
embankment with a masonry core wall to the right of the spillway and a low earthen dike to the left
ofthe spillway. There are several dams downstream of the Upper dam, including the Middle
Roberts Meadow Reservoir Dam (Middle Dam) and the Lower Roberts Meadow Dam (Lower
Dam). Previous studies by GZA have indicated that flows in the Roberts Meadow Brook will
overtop the Upper Dam during the SOD-year flood and pass through the Middle and Lower Dam
reservoirs without overtopping the dams. Flows from a dam breach at the Upper Dam during the
SOD-year storm would pass through the Middle Roberts Meadow Reservoir and over the Middle
Dam spillway and could slightly overtop (by 0.2 ft) the Lower Dam, potentially breaching that dam
and threatening lives, homes, and property downstream. Therefore, the Upper Dam is currently
listed as a High hazard potential dam by ODS.
Scope of Work
Our scope of work was as follows:
1. Perform a site visit.
2. Review relevant portions ofMassachusetts dam safety regulations.
3. Review existing studies, reports, presentations, correspondence and other relevant
information.
4. Based on items 1through 3, above, prepare a concise letter report which addresses the
following:
a. History ofthe hazard classification(s) ofthe Upper Roberts Meadow Reservoir Dam;
b. The overall completeness and degree of detail of the body of work to date;
c. The reasonableness ofthe existing inundation mapping prepared by GZA to assess the
probable impacts of failure of the Upper Roberts Meadow Reservoir Dam;
d. The appropriateness of the existing high hazard potential classification;
e. The feasibility of filing a request with ODS to reclassify the hazard potential;

3. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
-3- October 27, 2010
f. The estimated impact of reclassification to a lower hazard potential on existing cost
estimates to rehabilitate the dam to meet the design standards ofa high hazard potential
dam.
g. The estimated scope and cost to prepare and submit a hazard reclassification request to
the state.
Site Visit
GEl made a visit on October 21, 2010 to the Upper Roberts Meadow Reservoir Dam to view the
dam and the surrounding area. In addition to viewing the dam, portions ofthe upstream watershed
were viewed. The downstream channel, Middle Roberts Meadow Reservoir Dam, Lower Roberts
Meadow Reservoir Dam, and the Village of Leeds were also visited.
Massachusetts Dam Safety Regulations
The state dam safety regulations are codified in 302 CMR 10.00: Dam Safety. Several portions of
the regulations are relevant to the consideration of hazard classification.
Jurisdictional Status
First, it is important to determine whether the dam is regulated by the state, i.e., is it jurisdictional?
To be non-jurisdictional, a dam must be less than 6 ft high or store less than 15 acre-ft of water.
The Upper Roberts Meadow Reservoir Dam is about 30 ft high and stores about 19 acre-ft of water
(based on recent bathymetry) and therefore the dam is jurisdictional and will be regulated by the
state Office ofDam Safety.
Size Classification
The size classification ofthe dam drives several ofthe requirements ofthe regulations. The size
classification is determined by the height ofthe dam and the volume ofwater stored in the
reservoir, whichever gives the larger size classification. A dam 30 ft high with 19 acre-ft of water
stored falls into the Intermediate size category.
Hazard Classification
Hazard classification is assigned based on the likelihood for loss of life and!or property damage
should the dam fail (breach) either during a flood or on a sunny day. The Upper Roberts Meadow
Reservoir Dam has been assigned a hazard potential ofHigh.
• A high hazard potential dam by definition is "located where failure will likely cause loss of
life and serious damage to home(s), industrial or commercial facilities, important public
utilities, main highway(s), or railroad(s)" [320 CMR 10.06 (3)]. The other hazard potential
categories are Significant and Low.
• A significant hazard potential dam is "located where failure may cause loss of life and
damage home(s), industrial or commercial facilities, secondary highway(s) or railroad(s) or
cause interruption ofuse or service of relatively important facilities" [320 CMR 10.06 (3)].
• A low hazard potential dam is "located where failure may cause minimal property damage
to others. Loss of life is not expected" [320 CMR 10.06 (3)].

4. The Friends of the Upper Roberts
Meadow Reservoir and Dam
-4- October 27,2010
The dam safety regulations specifically address dams in series, such as the three Roberts Meadow
Dams. The regulations state: "If an upstream dam has the capability to create a failure in a
downstream dam because of its failure wave, it shall have the same or higher hazard classification
as the downstream dam" [302 CMR 10.06 (4) (a)].
The hazard classification drives the size of the storm that the dam's spillway should be able to
safely pass (without water flowing over the dam embankments and also from a stability
standpoint). For a high hazard potential dam, the "design" storm is one-half the Probable
Maximum Flood (1/2 PMF). The Probable Maximum Flood is "the most severe flood that is
considered reasonably possible at a site as a result of the most severe combination of critical
meteorological and hydrologic conditions possible in the region" [320 CMR 10.03 (2)]. A smaller
storm can be used for design or analysis if it can be shown that the increase in flood damage
downstream of the dam following a dam breach during that storm is less than about 2 ft greater
than the flooding damage from the storm without a breach or is less than 2 ft above the lowest
ground elevation adjacent to the outside foundation wall of an inhabited structure.
Condition
There are five condition categories for jurisdictional dams in Massachusetts. An inspection
schedule is prescribed based on the hazard classification (every 2 years for High, every 5 years for
Significant, and every 10 years for Low). The condition of a dam is assigned following an
inspection and can be one of Good, Satisfactory, Fair, Poor, or Unsafe. If a dam is in Poor or
Unsafe condition, the regulations permit ODS to order the dam owner to rehabilitate the dam to
bring it to Fair, Satisfactory, or Good condition.
Document Review
The documents reviewed by GEl are listed in Table 1. The Phase II report and the Emergency
Action Plan both refer to additional analysis details submitted by GZA under separate cover.
Unfortunately, those additional details were not available for review.
History of Hazard Classification
At one time in the past (prior to 1987) it appears that the Upper Dam may have had a "low hazard
potential" rating. However, according the GZA Phase I report prepared in 2006, a 1987 inspection
report prepared by the Massachusetts Department of Environmental Management estimated that a
failure ofthe Upper Roberts Meadow Reservoir Dam could cause a domino failure of downstream
dams. Therefore, GZA proposed that the hazard potential classification should be High.
In 2007, GZA prepared an Emergency Action Plan (EAP) for the Upper Roberts Meadow
Reservoir Dam. The EAP includes maps showing the areas downstream of the dam where flooding
is estimated to occur after a fair weather failure of the dam and after a failure during the design
storm (the 112 PMF). The results of GZA's analysis indicated that the Middle Dam and Lower
Dam would be overtopped by the flows from a breach (failure) ofthe Upper Dam and likely breach
also. The resulting flooding would impact several properties in Leeds. Therefore, GZA affirmed
their previous hazard potential classification of "High" for the Upper Roberts Meadow Reservoir
Dam.

5. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
Spillway Design Flood Estimate
-5-
The following presents a summary ofthe work perfonned by GZA.
October 27,2010
In 2008, GZA prepared a Phase II report on the Upper Roberts Meadow Reservoir Dam. This
report was prepared in response to an order from ODS to investigate the condition of the Upper
Dam and propose a plan for remediation of the darn, which had been found to be in Poor condition
in 2006. As part of the Phase II studies, GZA re-evaluated the potential for flooding downstream
of the Upper Dam from a failure of the dam during a flood. They evaluated flooding during the Y2
PMF, the 500-year flood, and the IOO-year flood. They concluded that the Upper Dam would be
overtopped during by all three floods and could potentially breach. However, for the IOO-year
flood the depth of overtopping over the earth embankment was calculated to be only 0.6 ft. The
duration ofthe overtopping was not given. GZA also concluded that the Middle and Lower Dams
would be overtopped during the Y2 PMF whether or not the Upper Dam failed. For the 500-year
flood, the Middle Dam would not be overtopped whether or not the Upper Dam failed and the
Lower Dam would be overtopped slightly (by 0.2 ft) ifthe Upper Dam failed, but would not be
overtopped if the Upper Dam did not fail.
GZA then estimated the extra flooding that a failure ofthe Upper Dam would cause if it failed
during the 12 PMF or the 500-year flood. They estimated that a failure ofthe Upper Dam during
the 112 PMF would cause less than 2 ft of additional flooding throughout the downstream area to
the Village of Leeds. However, for the 500-year flood, GZA computed a failure of the Upper Dam
would cause 2 to 3 ft ofadditional flooding over that caused by the stonn without failure. This
additional flooding would occur downstream ofthe Lower Dam as a result of it being overtopped
by 0.2 ft and subsequently failing.
On the basis ofthese findings, GZA suggested that the 500-year flood be designated the Inflow
Design Flood, instead of the 12 PMF. [For comparison, in the Regulations, the Inflow Design
Flood for a Significant Hazard potential dam is the IOO-year flood and for a Low Hazard potential
dam is the 50-year flood. The current spillway at the Upper Dam cannot safely pass the IOO-year
flood, but the costs would likely be much less to improve the dam to pass the IOO-year flood rather
than the 500-year flood.]
Evaluation of Completeness of Prior Studies
In general, the analysis methods used by GZA were appropriate and the dam breach parameters
assumed in the analysis were reasonable. There are one or two areas where the analyses could be
refined:
1. A May 2009 presentation by the Northampton Department of Public Works (DPW) and GZA
included a bathymetric survey of the Upper Roberts Meadow Reservoir that showed the
impoundment is silted in (the exact date of the survey is unknown). Prior to that survey, the
nonnal capacity of the reservoir was estimated to be 35 acre-ft (approximately 11.5 million
gallons). After the survey, the nonnal capacity of the reservoir was estimated to be 19 acre-ft
(approximately 6 million gallons). In the 2007 EAP, GZA states that they assumed a nonnal
capacity of 35 acre-ft. Although the 2008 Phase II report doesn't explicitly state the storage
capacity assumed in the dam failure analyses, we assume the same capacity of 35 acre-ft was
used. Therefore, ifthe dam break analysis was to be redone with the smaller reservoir
storage capacity used, it is possible that the incremental flooding from a dam break during a
500-year flood would be less than 2 ft. It would then be reasonable to estimate the

6. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
-6- October 27,2010
incremental flooding from a failure during the 100-year flood to estimate whether the 100-
year flood might be a suitable design flood.
2. GZA used the computer program "DAMBRK" to perform the dam failure analysis and
estimate the downstream flooding. An alternative computer program that could be used
today would be HEC-RAS. One advantage ofusing HEC-RAS is that more detailed
topographic information can be developed to more accurately define the geometry of the
stream channel downstream of the dam using a geographic information system (GIS). In
fact, the City ofNorthampton has mapping with 5-ft contour intervals available. GZA used
USGS topographic maps with 10-ft contour intervals (which may have been the only
information available at the time).
Evaluation of the HEC-RAS results is enhanced by exporting the peak water surface
elevations into GIS over a digital elevation model (DEM). The GIS software automatically
delineates the inundated areas and allows us to efficiently compare and evaluate potentially
impacted structures, properties, roads, etc. The incremental impacts are assessed by
comparing the dam failure versus the non-darn-failure conditions.
Although we do not know how many or how detailed the cross sections were that GZA used
in their DAMBRK model, it is possible that the use of additional cross sections may allow
better definition of the fairly flat area upstream of the Middle Dam. This flat area could store
flood water and attenuate the flood wave as it travels downstream. An attenuated flood could
result in less incremental damage or fewer impacts, which provide justification for
reclassifying the hazard potential ofthe dam. Using the 5-ft contour map available on the
City ofNorthampton website, we computed an area ofabout 72 acres between the Upper and
Middle Dams at El. 405, the elevation ofthe emergency spillway at the Middle Dam. The
spillway crest at the Middle Dam is about El. 399, implying that there is approximately 430
acre-ft of storage available above the Middle Dam spillway crest before the emergency
spillway at the Middle Dam would be activated.
Appropriateness of High Hazard Potential Classification
Based on the work completed to date, it is our opinion that the High hazard potential classification
was appropriate. However, it appears that the prior work was based on a storage capacity of 35
acre-ft rather than the storage of 19 acre-ft that is currently in the reservoir, accounting for siltation.
If the reservoir is to remain a recreational asset and is not dredged, it would be appropriate to
compute the downstream flooding effects using the lower storage volume. This reanalysis might
justify a lower hazard potential rating such as Significant. However, it is our opinion that we
would not be able to show that the hazard classification should be "Low," because breach flows are
likely to flood and potentially damage the adjacent secondary roads (Chesterfield Road and/or
Reservoir Road).
Feasibility of Filing a Hazard Reclassification with ODS
The Office of Dam Safety has a procedure for requesting a hazard classification change. The
requesting party will need to provide data and calculations that justify that change. In this case the
basis for pursuing the hazard classification change would include: the more detailed topographic
data; the reduced reservoir storage as estimated from the bathymetric survey performed since the
2008 Phase II report was completed; and possibly the opportunity to use the HEC-RAS model.
The bathymetric data were presented in the 2009 and 2010 presentations by the Northampton DPW

7. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
-7- October 27,2010
and GZA. Ifthe Friends cannot obtain the bathymetric data, a new bathymetric survey will need to
be completed to update the DAMBRK model used in the previous study. Ifthe DAMBRK model
is not available, the dam failure analysis and hazard classification evaluation should be evaluated
using recent bathymetric data, HEC-RAS, and GIS.
Impact of Reclassification to a Lower Hazard Potential on Existing Cost Estimates
to Rehabilitate the Dam
The Upper Roberts Meadow Reservoir Dam is in Poor condition and several of the deficiencies
will need to be addressed regardless ofthe hazard potential classification. These deficiencies
include:
• Trees and other vegetation on the embankments and dike.
• Seepage through the spillway masonry blocks.
• Seepage through the right embankment, particularly along the spillway retaining wall.
• Sinkholes on the right embankment crest.
• The loose fill upstream and downstream ofthe masonry core wall at the right embankment.
• The lack ofa functioning low-level outlet.
If the dam is reclassified to a Significant hazard potential dam, the spillway will need to be
enlarged to safely pass the 100-year flood or the right embankment and left dike will need to be
raised to prevent overtopping or hardened to allow flow over the top without washing out the
embankment fill. However, the spillway enlargement or embankment modifications will be
significantly less expensive for a 100-year flood rather than a SOO-year flood.
In addition, the stability analyses performed by GZA indicated that the masonry spillway was not
stable for several required loading cases unless three-dimensional buttressing effects (due to the
dam's curved shape) were included. We did not review the GZA stability analyses in detail, but
changing the design flood from SOO-year flood to 100-year flood mayor may not resolve the
stability issue. GZA used a simplified method to account for the 3-dimensional effects ofthe
curved shape. A more detailed 3-dimensional evaluation might show that the dam can meet
stability criteria.
Although we cannot predict the full extent ofthe dam modifications needed without performing the
additional spillway design flood/dam breach and stability analyses, it is our opinion that the costs
to rehabilitate the dam if it is reclassified to Significant hazard potential would be less than half the
costs to perform the full rehabilitation costs estimated by GZA for the High hazard potential
classification.
Given that the Lower Dam is only slightly overtopped (by 0.2 ft) by the breach ofthe Upper Dam
during the SOO-year flood, it would be relatively inexpensive to raise the crest of the Lower Dam, if
needed. .

8. The Friends ofthe Upper Roberts
Meadow Reservoir and Dam
-8- October 27,2010
Estimated Scope and Cost to Prepare and Submit a Hazard Reclassification
Request to the State
We have not prepared a detailed cost estimate to prepare and submit a hazard reclassification to the
state. However, we can provide the following approximate budget numbers:
Re-perform Inflow Design Flood/Dam break
studies to estimate the IDF
Prepare and submit application to ODS
Bathymetric survey (if needed)
$25,000
$10,000
$10,000
We have not provided a cost for additional ground survey work because we do not think it is
necessary at this time.
We appreciate the opportunity to be of service. Please let us know if we can provide any additional
assistance.
Sincerely,
GEl CONSULTANTS, INC.
Gillian M. Gregory, Ph.D., P.E.
Senior Project Manager
GMG/rr
M:PROJECf201O 10426Upper Roberts Meadow Dam Leeds MA Ltr Rpt Final.docx

9. Table 1 - Documents Reviewed by GEl
Department of Public Works (2009). "Project Update, Upper Roberts Meadow Dam," City of
Northampton, September 9.
GZA GeoEnvironmental, Inc. (2006). "Phase I Inspection/Evaluation Report, Upper Roberts
Meadow Reservoir Dam, Northampton, MA," prepared for Northampton Department of Public
Works, March.
GZA GeoEnvironmental, Inc. (2008). "Phase II Engineering Evaluation & Alternatives Analysis,
Upper Roberts Meadow Reservoir Dam, Northampton, MA," prepared for Northampton
Department of Public Works, March.
GZA GeoEnvironmental, Inc. (2007). "Emergency Action Plan, Upper Roberts Meadow Reservoir
Dam," prepared for City ofNorthampton, August.
GZA GeoEnvironmental, Inc. (2009). Upper Roberts Meadow Dam Presentation 20090520,
prepared for Northampton DPW, May.
GZA GeoEnvironmental, Inc. (2010). Final Upper Roberts Meadow Dam Presentation 20100120,
prepared for Northampton DPW, January.
The Essex Partnership (2010). Letter to Mayor ofNorthampton, Northampton Board of Public
Works, and Friends ofthe Upper Roberts Meadow Reservoir Dam, August 27.