Christian Science Monitor: “How to plan better for New England floods”

The April 3 Christian Science Monitor uses the occasion of the recent flooding along the New England coast to look at climate trends:

How to plan better for New England floods  

As flood waters recede in rain-soaked New England, March’s record-smashing storms highlight the need for planners in the region to place an increased emphasis on reducing flood risks and boosting their communities’ resilience to floods…

Planners need to update the basic information on rainfall intensity they use to determine the adequacy of their projects.

That’s the view of several hydrology specialists, who note that changing rainfall patterns in the area alone have increased the number of floods and appears to have increased their average severity as well over the past 40 years – particularly in the last decade…

[click for the complete article]

The Kohl Construction condominium proposal  for North Street relies heavily on stormwater assumptions (see PDF) that may be outdated. Kohl assumes that a typical 24-hour 2-year rainfall is 2.95″, a 10-year rainfall is 4.45″,  and a 100-year rainfall is 6.50″. Maybe this is still true, but when you build as close to wetlands as Kohl proposes to, there’s little margin for error.

See also:

Springfield Republican: “Northeast seeing more, fiercer rainstorms in line with global warming predictions, study says” (4/5/10)
Healthy wetlands and wetlands buffers mitigate flooding. Compared to manmade stormwater infrastructure, wetlands are cheap, effective, and low-maintenance forms of flood control. Scientific studies suggest wetlands need 50-foot buffers or more to retard degradation from human activity.

Gazette: “Region’s storms going to extremes, report finds” (12/5/07)

City Council Enacts New Wetlands Ordinance, Including 10-Foot Buffers
We believe…that our in-town buffers are more important than average when it comes to flood mitigation and water pollution. A disproportionate percentage of the people and property of the city are found in the areas now subject to 10-foot wetlands buffers. Our drainage systems there are already under stress. Flood damage reports from Tropical Storm Floyd show clusters of red flags in our urban areas, even under the previous, more restrictive buffer zone regime.

Comparing the New Hazards Mitigation Plan to the Old One: Wetlands Protection Weakened (11/2/08)
We compared the new Plan to the existing one, which the City Council signed off on in 2004. We gave special attention to wetlands regulations. Wetlands play a valuable role in mitigating both floods and droughts.

The 2004 Plan specifically mentions the regulation of development within 100-foot buffer zones around wetlands as an effective flood mitigation strategy...

Unfortunately, the City Council voted 7-2 in 2007 to permit development in multiple districts to encroach as close as 10 feet to wetlands. In a rapid shift of priorities, facilitating urban infill was now deemed more important than flood mitigation, water pollution control, or urban greenspace. The proposed condo development off North Street is a good example of a project that relies on the narrowed buffer zones.

The 2008 Hazards Mitigation Plan reflects the weakened wetlands protection by leaving out all mention of 100-foot buffer zones. Instead, it merely refers readers back to the Wetlands Ordinance and continues to claim it is “effective at limiting development that would harm these resources.”

Most striking in the [Environmental Law Institute] report is that some locales desire wider buffers in areas of intense land use to address the higher levels of pollution and runoff. By contrast, Northampton has its narrowest buffers in these areas.

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.

[The new Hazards Mitigation Plan states:] The last hurricane to make landfall in New England was Hurricane Floyd, a weak category 2 hurricane, in November 1999. Therefore, 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.” (p.28, emphasis added)

As Hurricane Threat Builds, Has Complacency Set In about Flooding?
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.