Date of Inspection: June 25, 1998

By: Hydraulic & Water Resources Engineers for DEM Office of Dam Safety

General Notes: Assessment of Dam was based on the general conditions and available data and visual inspections. The inspection was required because a previous report in 1987 by Camp Dresser and McKee, Inc. reported that there were serious structural, and/or hydraulic and/or emergency action plan deficiencies.

Findings from visual inspections (at time of inspection the water elevation was 158.0 MSL (mean sea level) or 4 feet below the top of the dam)

  1. Evidence of extensive seepage and rust stained wet areas were observed along the downstream toe in the area right of the emergency spillway. Wet areas were also present along the downstream toe to the left of the spillway where the Mill Brook flows adjacent to the toe of slope.
  2. Spalling and mortared joints and missing stones were observed in the emergency spillway training walls and outlet channel. There is erosion of the embankment at its contact with the left training wall.
  3. A crack and spalled area on the left concrete sidewall of the principal gated spillway was found. There is a 4-inch diameter hole in the tainter gate.
  4. Riprap was absent and localized erosion from wave action was evident along the upstream slope of the dam.
  5. It is unknown whether or not the low-level outlet is operational.
  6. Trees and debris are blocking the spillway outlet.
  7. Heavy tree and brush growth make it difficult to monitor the condition of the dam and to observe sinkholes, cracks, slides or animal burrows on the upstream slope of the dam.
Summary of Recommendations
  1. Implement a regular inspection program to monitor any changes in the condition of the dam.
  2. Remove trees and brush on the slopes of the earth embankment. Fill stumpholes with compacted granular fill on downstream slope and compacted impervious fill on the upstream slope.
  3. Remove trees, brush and debris and repoint the spalled mortared joints in the emergency spillway channel.
  4. Provide riprap slope protection on the upstream slope of the embankment particularly where erosion of the shoreline has occurred.
  5. Repair the spalled concrete and crack on the left sidewall of the spillway
Estimated cost to complete work: $188,000 to $270,000

General Description of the Arlington Reservoir Dam

The Arlington Reservoir Dam is an earth embankment With a minimum top width of 20 ft. The dam impounds water from the Munroe Brook and has a drainage area of 2.36 square miles. The reservoir was built in the late 1800's and used for water supply for the town. The spillway crest gate was built from 1957 to 1958.

The Arlington Reservoir Dam is presently used for recreation and flood control. The overall length of the dam embankment is 1770 feet and is located between Lowell Street and the Boston and Maine Railroad tracks (Minuteman Bikeway) at the Arlington and Lexington town lines. The dam is an intermediate size dam. There is a housing development immediately downstream of the dam and therefore the dam is classified as Class 1, (high) hazard dam. The responsibility for operation and maintenance of the dam lies with the Arlington Department of Public Works.

Dam includes:

  1. Crest Gate Spillway with concrete sidewalls and wingwalls is located 80' to left of emergency spillway. Gate can be raised from elevations 153 MSL to 159 MSL with its crest 3 feet from below the top of the dam. It is manually operated. Overflow passes into a 60 inch diameter, 70 foot long concrete pipe and then into the Mill Brook.
  2. Emergency Spillway is a stone and mortar channel which is about 20 feet wide and 3 feet deep. Overflow from this spillway also empties into Mill Brook. A steel service bridge in general disrepair spans the spillway.
  3. Low level outlet is located about 800 feet to the left of the crest gate spillway. The low level outlet empties into a 12" pipe which then empties into a 15" concrete storm drain which then empties into the Mill Brook.
  4. An earthen embankment 1770' feet long which has a structural height from the dam crest to the lowest downstream slope of approximately 14 feet (only an estimate). The top of the embankment is 162 MSL. Top of the dam downstream is 148 MSL. The maximum storage capacity is approximately 480 acre feet. The reservoir has a surface area of 65 acres.
Operation procedures:
  1. Crest gate of sluiceway is used to regulate the surface water elevation of the reservoir from elevations 159 MSL to 153 MSL.
  2. Low level outlet (~ 148 MSL is used to draw the reservoir even lower.
Previous studies and reported problems:
  1. 1981 by ASEC Corporation and 1987 by Camp, Dresser and McKee, Inc.
  2. Previous concerns from hydraulic/hydrologic data from both studies: distinct potential for overtopping the dam and the spillway is capable of passing not more than 48% of the Storm Design Flood (based on a 1/2 PMF storm event (I think a 500 yr. storm)).
Proposed Scope of Services for town funded study:
Inspect the conditions at the dam and identify two repair options and a cost estimate for selected repair option. Perform a hydraulic and hydrologic study to evaluate the spillway capacity of the dam. Neither an Emergency Action Plan nor an Operation and Maintenance plan will be completed.

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