Reservoir Consultant's Report

by Mohammad Kheirallah, February 2000

SECTION 1:  INTRODUCTION
  1. Site Description

    Arlington Reservoir Dam is located between Lowell Street and the Boston and Maine Railroad tracks on the town lines of Arlington and Lexington (see Figure 1 for dam location). The dam impounds water from Monroe Brook. The Town of Arlington Department of Public Works owns and operates the dam. The dam was constructed prior to 1900 with the spillway modified in 1957 and 1958. No construction documents are available for the original design.

    The earth-filled embankment dam was originally constructed to provide water supply for the town of Arlington; however, it is currently used for recreation and flood control purposes. The dam has an average top width of approximately 20 feet, a maximum height of about 14 feet, and upstream and downstream slopes ranging from a minimum 2.5H:1V to 1.5H:1V. The overall length of the dam is approximately 1,770 feet, including a 9-foot wide emergency spillway with a concrete crest located near the center of the dam.

    The dam contains a crest gate spillway (principal spillway), an emergency spillway, and a low-level outlet. The emergency spillway is located about 400 feet from the right end of the dam and the crest gate is about 20 feet to the left of the emergency spillway. The low-level outlet is located about 800 feet left of the crest gate spillway.

    The principal spillway has concrete sidewalls with concrete wing walls in the approach area. The gate is 9 feet long and can be raised a total of 6 feet from its lowest position at elevation 153 feet. At its fully raised position (elevation 159 feet), the spillway crest is 3 feet below the top of the dam. A concrete slab spans the top of the sidewalls of the spillway just upstream from the crest gate. The gate can be raised and lowered manually by a worm drive mechanism located on the concrete slab. A security fence encloses the crest gate and worm drive mechanism. Overflow from the spillway passes into a 60-inch diameter, 70-foot long concrete pipe and ultimately into Mill Brook.

    The emergency spillway is a stone and mortar channel that is about 20 feet wide and 3 feet deep. Overflow from this spillway empties into Mill Brook. A steel service bridge spans the spillway.

    A 12-inch diameter pipe controlled by a gate valve serves as a low-level outlet for the dam and is located about 800 feet to the left of the crest gate spillway. According to Department of Environmental Management (DEM) reports, the 12-inch outlet connects to a 15-inch concrete storm drain, which then empties into Mill Brook. The gate valve is reported to be operational and is housed within a brick chamber on the crest of the dam, which was built below grade and can be accessed through a manhole at the top of the chamber.

  2. Engineering Data

    The following sections are based on information obtained from available reports and are intended to provide an overview of the impoundment. We have checked the accuracy of some of this information (dimensions, elevation, etc.) based on our visual observations in the field. Other information was not verified, as it was outside the specified scope of work.

     

    1. Drainage Area
    2. The drainage area for Arlington Reservoir Dam is approximately 1.75 square miles.

    3. Reservoir
      1. Dimensions (feet)
      2. A. Length of normal pool: 1,150

        B. Width of normal pool: 800

        C. Length of pool at top of dam: 1,850

        D. Width of pool at top of dam: 1,000

      3. Storage (acre-feet)
      4. A. Normal pool:

        At Elevation 153 75

        At Elevation 159 246

        B. Top of dam: 494

      5. Surface (acres)
      6. A. Normal pool: 29

        B. Top of dam: 43

      7. Additional Elevations (feet)
      8. A. Top of dam: 162 MSL

        B. Normal pool: 153 to 159 MSL

        C. Spillway crest, gated: 159 MSL

        D. Spillway crest, ungated: 153 MSL

        E. Emergency spillway crest: 159 MSL

        F. Downstream water: 148 MSL

      9. Main Spillway

        A. Type: Spill Crest Gate

        B. Length of weir: 9 feet

        C. Crest elevation (gated): 159 MSL

        D. Crest elevation (ungated): 153 MSL

        E. Upstream channel: Arlington Reservoir

        F. Downstream channel: Flows into 5-foot diameter concrete pipe and exits to Mill Brook

         

  3. Regulatory Classifications

     

    1. Size Classification
    2. The maximum storage capacity of Arlington Reservoir Dam is approximately 494 acre-feet at maximum pool, as calculated in the Phase I Inspection Report prepared by ASEC Corporation and a structural height of approximately 14 feet, measured from the dam crest to the lowest point of the downstream slope. In accordance with Department of Environmental Management (DEM) classification, under the December 27, 1996, DEM Code of Massachusetts Regulations 302 CMR Dam Safety Rules and Regulations, Arlington Reservoir Dam is an Intermediate size dam.

    3. Hazard Classification

There is a housing development immediately downstream of the dam. In the event of dam failure, loss of more than a few lives and excessive property damage is likely. As a result, under DEM Guidelines, Arlington Reservoir Dam should be classified as a Class I (High) hazard dam.

 

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