Northampton - Winter Street - Review Letter
4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com
Berkshire
Design
Group
June 16, 2022
Rose Nieboer
29 Winter Street
Northampton, MA 01060
RE: Review of City Drainage Design & Alternative Drainage Designs
Winter Street
Dear Ms. Nieboer,
At your request, Berkshire Design has reviewed the documents you provided that summarize a project
proposed by the Northampton Department of Public Works, on Winter Street in Northampton.
The following documents were reviewed:
· Notice of Intent – Drainage Improvements to Winter Street, Northampton, Massachusetts, dated April
15, 2022 (NOI).
We reviewed the project narrative, including alternatives analysis, and the plan sheets included in the NOI. We
have prepared the following comments.
1. We agree with DPW that their proposed Alternative 1 is not feasible due to the requirement to
separate stormwater flows from the sanitary sewer. This will necessarily increase stormwater flows
from the street. We also agree that the increase in runoff to the downstream wetland system is small
as a percentage of total water flows to the wetlands and it is our opinion that any impacts to adjacent
properties from this increase will be negligible.
2. Alternative 2, which proposed new catch basins and storm drain in Winter Street with an engineered
outlet at the eastern edge of the site, was dismissed due to higher cost, engineering challenges, and
increased impacts to the wetland buffer area. We acknowledge that construction of this alternative
would incur higher capital costs and create more wetland buffer impacts, but the NOI overlooks some
advantages of this alternative. The presence of catch basins ensures some level of water quality
treatment (25% TSS removal per the Massachusetts Stormwater Handbook). The City already provides
scheduled maintenance for catch basins and storm drains, so some level of maintenance would be
assured to occur as part of existing programs. The NOI narrative notes that a new outfall would
“require ongoing maintenance to ensure it continues to function properly”. As discussed elsewhere in
this letter, any alternative proposing new stormwater features will require maintenance to ensure
functionality. A properly designed level spreader would ensure low-velocity sheet flow discharge and
would require similar maintenance to the proposed gravel spreader if functionality is to be maintained.
(See also #4 and #5 below regarding maintenance.)
3. We have concerns about the selected alternative, which would create a compacted gravel pad at the
downslope end of the road and is intended to spread out stormwater flows and reduce velocity before
discharge toward the wetlands to the east. The proposed pad is described as a “level spreader” in the
NOI narrative; however, a true level spreader includes a length of flat curb or other solid material at the
discharge end that promotes sheet flow and is resistive to erosion. With a surface made entirely of
aggregate, we would expect the stormwater flows to concentrate in low areas over time and erode
channels, which would progress with each heavy rainstorm and thus undermine the ability of this pad
to spread out stormwater. Winter snow plowing is likely to exacerbate these issues.
June 16, 2022
Review of City Drainage Design & Alternative Drainage Designs
Winter Street
Page 2 of 2
4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com
Additionally, the paved portion of Winter Street is proposed to be crowned and curbed. During intense
rainfall gutter flows will be relatively large and the transition point between the guttered pavement
and the flat gravel spreader will be particularly vulnerable to erosion.
4. We note that the NOI does not include a clear maintenance plan for the gravel spreader. The NOI
described the proposed gravel as a “level spreader”, which is a stormwater BMP listed in the
Massachusetts Stormwater Handbook. Conversely, the drainage report states that no stormwater
management is proposed, and that the area will be “monitored” along with the rest of the street under
DPW’s street management operation. An Operation and Maintenance Plan is typically required for
stormwater projects approved by the City, so it would be expected that on-going maintenance would
be a requirement for this project. At a minimum, periodic inspection that specifically reviews the site
for erosion or collection of sediment, followed by repair if required, would be needed to ensure
continued functioning of the gravel spreader over the long term.
5. We would suggest an additional alternative that does not appear to have been considered by DPW at
this location. We can appreciate the difficulty and expense of designing and constructing a new storm
drain and outfall for Winter Street that was considered as Alternative 2. Instead, we suggest exploring
an alternative that keeps stormwater on the surface, but discharges it through a true engineered level
spreader, designed per the Massachusetts Stormwater Handbook, and located toward the eastern end
of the new right of way. The design would need to consider how to convey gutter flows to the new
level spreader, but it is our opinion that this design challenge could be solved with proper grading and
selection of materials.
A true level spreader would require no more maintenance than would be required to keep the
proposed gravel spreader functional, while still avoiding the need for maintaining catch basins and
storm drain piping. Per the Handbook, maintenance should consist of: Inspect level spreaders regularly,
especially after large rainfall events. Note and repair any erosion or low spots in the spreader.
6. We recommend that accessibility to the walkway at 29 Winter Street be reviewed. The existing
compacted gravel driveway is not, strictly speaking, an ADA-accessible walking surface. However, we
understand that the gravel has provided suitable pedestrian access to the walkway. Plans for the
proposed gravel spreader specify “4-inch minus dense graded crushed stone”. We note that the 4-inch
maximum stone size may provide a poor walking surface for an elderly or low-mobility person.
Generally, a smaller maximum stone size would provide a preferred surface. A true ADA-accessible
aggregate surface would require the use of stone dust or decomposed granite, both of which would be
more likely to erode and would not be recommended for this application. It is our opinion that a dense
graded gravel with a smaller maximum stone size would be an appropriate middle ground.
Sincerely,
Berkshire Design Group
Christopher Chamberland, P.E.
Principal