New England Climate Change: More Rain on Snow Will Challenge Stormwater Management

Stormwater modeling calculations, such as those found in the Kohl condo proposal for North Street, typically leave out a number of common scenarios. One of the most challenging of these is managing the flow from rain that falls on snow. Frozen ground doesn’t absorb water well. Snow can plug up pipes and grates and interfere with landscape grading that directs water towards catchment systems. Unfortunately, more rain on snow is what New England can expect due to climate change. USA Today reported on 7/30/04:

Study: New England now getting less snow, more rain

Snowfall in New England has decreased significantly in favor of rain during the last half of the 20th century, according to a study by the U.S. Geological Survey….

“We’re likely to see an earlier snow melt and more rain on snow,” [said Thomas Huntington, a USGS hydrologist in Augusta and the study’s lead author]…

Previously published studies of late winter and early spring hydrologic changes in New England during the past century showed a one- to two-week advance in the halfway point of the winter-spring runoff and large increases in February river flows coupled with decreases in May flows, suggesting earlier snowmelt.

[Caveat: The study included data from locations in Maine, New Hampshire, Vermont, Rhode Island and eastern Massachusetts. Sites in Connecticut and western Massachusetts lacked sufficient data to meet the study’s criteria.]

Another aspect of climate change is an increase in the frequency of extreme downpours and snowstorms in the US, with the highest increases in New England. The 12/5/07 Gazette reports:

Massachusetts saw a 67 percent rise in severe storms during [1948-2006], trailing only Rhode Island and New Hampshire…

…the top 10 severe storms in the state all occurred in the past decade…

…scientists expect that extreme downpours will punctuate longer periods of relative dryness, increasing the risk of drought…

The changing nature and distribution of precipitation in New England are two excellent reasons to preserve and even enlarge the buffer zones around our urban wetlands. We need healthy wetlands more than ever to absorb stormwater and moderate extreme precipitation events. Proposals like Kohl’s, that call for a great deal of disturbance and encroachment inside the 35-foot buffer zone, are taking the city in the wrong direction.

See also:

Flood and Natural Hazard Mitigation Plan: Floyd Flood Damage Reported
Behind View Avenue; Avoid Building on Filled Wetlands

In the map
below, the red flag behind View Avenue (the topmost flag) indicates a
flood damage report from Tropical Storm Floyd (1999). This area is in
the eastern portion of Kohl Construction’s proposed condo site, one of the more elevated portions. We infer that much of Kohl’s property may be at risk from heavy rainfall events.

Easthampton Flooding Hazard: Snow-Clogged Storm Drains
“If the water has nowhere to go, it’s going to find somewhere to go… The slush really clogs [storm drains].”

Snow and Slush Expose Limits of Storm Drains
…”The rainfall carries floating slush to a catch basin,” said Amherst
Public Works Superintendent Guilford Mooring. “We clear something up
and it clogs up again. We’ve been working since last night.”

for Easthampton Public Works Superintendent Joseph I. Pipczynski: “It’s
just a nasty storm,” he said. “You unplug the basin, they go down the
street, the slush covers the basin again and you’ve got another lake…”

Video: “Low Impact Development: Performance Results and Implementation in the Field”; Summer vs. Winter Performance of Stormwater Systems
Here are selected excerpts from Dr. Roseen’s presentation (0:13:30-0:32:12):

0:23:36-0:27:59: Summer vs. winter
performance of various stormwater systems. Pointing to a chart showing
removal of total suspended solids (TSS): “So here’s our [stone-lined]
swale. This is probably 98% of what’s out there. It’s doing fine in the
summer. It does nothing in the winter.” “If you consider the EPA is in
general is looking at 80% removal efficiency for TSS, our conventional
practices [such as stone-lined swales and wet ponds] are not meeting

0:29:36… “How are you going to balance public
safety with aquatic habitat? We know we’re going to go with public
safety. So, salt reduction is not the simple answer… and there’s no
way to treat salt with a stormwater BMP.” Roseen goes on to recommend
consideration of porous pavements. They let you use less salt and still
prevent slippery surfaces.

Kohl Construction’s application
(PDF) to build condos near the wetlands off North Street provides a
Stormwater Drainage Report and a Stormwater Management Plan (pages
27-185). In light of Dr. Roseen’s research findings, the winter
performance of Kohl’s proposed stormwater systems needs much more
Not only is water quality an issue, but also flood
control, as ice, snow and slush are well known to impede the smooth
flow of water.

On page 152 of the application Kohl asserts,
“The use of sand or deicing materials shall not be excessive.” Since
public safety is generally top priority in practice, however, this
seems like a thin safeguard for water quality.

Video of December 11 Kohl Condo Hearing at Conservation Commission
Kohl proposed to place grading, walls, yards, patios, and certain components of the stormwater
management system as close as 12 feet to the wetland
on its parcel… The commission expressed discomfort with allowing much disturbance closer than 35 feet to the wetland…

Commissioner Downey Meyer, “I’m also not inclined
to go below 35 feet. I also wonder why those who have spoken so quickly
got to 50, since the state Wetland Protection Act and the city
ordinance both protect to 100. So I think you’re being rather
unambitious arguing from 50 to 35… I’m also, as Alex said, a little
bit skeptical of the engineered solutions… Part of the reason why
buffer zones have received greater emphasis in wetlands protection is
that they do seem to work without anyone having to maintain them in
terms of making the whole wetlands system work effectively. However, in
terms of extraordinary mitigation, I think that to leave open what
could happen within 35 feet, I think that depending on the size of the
impact within the 35-foot boundary, then the extraordinariness of the
mitigation would be in relation to that. Obviously here you have the
creation of some of these detention ponds within the 35-foot area. If
you were talking about pipes or drywells within the 35 feet, and there
was some significant or extraordinary mitigation in relation to that
minor incursion, that’s a different calculus…  The extraordinariness
of the mitigation is to be balanced against the size of the incursion.
I would think that’s the only way the commission can look at it. They
couldn’t just say, ‘There’s one extraordinary measure you must go
through regardless of what you do within 35 feet…'”

New Hazards Mitigation Plan Reflects Weakened Protection for Wetlands
The claim that allowing development within 50 feet of wetlands can
still give effective protection does not bear up under scientific
scrutiny. As Hyla Ecological Services noted in 2007:

“Buffers of less than 50 feet in width are generally
ineffective in protecting wetlands. Buffers larger than 50 feet are
necessary to protect wetlands from an influx of sediment and nutrients,
to protect wetlands from direct human disturbance, to protect sensitive
wildlife species from adverse impacts, and to protect wetlands from the
adverse effects of changes in quantity of water entering the
wetland…” (Castelle et al., ‘Wetland Buffers: Use and Effectiveness’,

Earlier this year, NSNA engaged Hyla to
compare Northampton’s new Wetlands Ordinance to the regulations in
other cities across Massachusetts. Hyla found that Northampton is now an outlier. In the entire state, it’s hard to find anything similar to our 10-foot buffer zones for new development…

“…it is forecasted that, Massachusetts,
and the rest of New England, is long overdue for a major hurricane to
make landfall. Based on past hurricane and tropical storm landfalls,
the frequency of tropical systems to hit the Massachusetts coastline is
an average of once out of every six years.” (Hazards Mitigation Plan, p.28)

As Hurricane Threat Builds, Has Complacency Set In about Flooding?
Bastardi, AccuWeater:] New England is fair game from now on until 2025,
although the most frequent threats to the Northeast should be later in
the run of the cycle… I believe we are in the early to middle stages
of the AMO [Atlantic Multidecadal Oscillation]…

Infill sounds
great on paper, but when it means paving over green space in downtown
Northampton, it runs contrary to sound flood mitigation practice. The
reality is that much of the remaining green space in downtown is in
low-lying areas that are most susceptible to flooding. It makes sense
to go along with the collective wisdom of the past 350 years and leave
them undeveloped.

American Meteorological Society Press Release: Is Less Snow in New England’s Forecast? (7/26/04, PDF)