The Baker Dam is particularly problematic since floodwaters back-up behind the dam, raising floodwater levels during major storms and causing water to spill over onto the Neponset Greenway bikepath, the MBTA tracks and during larger floods, into the Milton Landing area, into the planned Baker Square Condominium common area near the dam and, under certain conditions, and into the Baker Square parking area. Making matters worse, these floodwaters would likely be carrying a load of toxic river-bottom sediments.

The Department of Conservation and Recreation recently completed dam safety engineering inspection reports on the Baker and T&H Dams. These were the first formal dam safety inspections completed on these dams in approximately 26 years. Those inspection reports recommended increasing the flood hazard classification for both dams to “significant” because the failure of one or both of these dams would create additional flooding and may contribute to the loss of life and damage to property and infrastructure.

The Baker Dam is more problematic in terms of its failure potential because of its close proximity to the historic mill buildings in the Lower Mills area, with the dam actually being an integral part of the foundations of two of the historic buildings.

Since the dams were completed in the mid-1960s, there have only been two significant flood events on the Neponset River, in 1968 and 1998. Each of these storms was a relatively modest flood event, at or below the 40-year flood level as estimated by the US Geological Survey upstream. The Baker Dam flooded the railroad tracks and bike path during both of these events, with 1968 being a major overflow and 1999 a more minor overflow. During 1968, flooding also inundated the Milton Landing area.

The recent dam safety inspection reports for the dams indicate that the Department of Conservation and Recreation, which owns and operates the dams, has no operations manual for the dams, no operating records, no emergency operating plans, no emergency action plan and no design plans or hydraulic data for either of the dams.

Recently updated bathymetry data show that the flood storage capacity of the T&H Dam is only 60 acre-feet, even using the most optimistic assumptions. Analysis of the hydrograph by Milone and MacBroom Inc. estimates that, at best, the T&H Dam has the capacity to store only 0.15% of the 100-year flood volume and reduce the peak discharge rate by approximately 0.14%. Expressed another way, if the T&H Dam were completely drained before the commencement of the storm and the gates were raised at just the right moment to shave the peak off the “floodwave,” it would take less than 15 minutes for the pond to refill.

Additional Flooding Information

Under Construction: Slideshow of historic photos (hyperlink to come)

Under Construction: Links to 1968 USGS study (hyperlink to come)

January 2008