“UMass geologists: New England may be facing higher risk of flooding as groundwater levels rise”

Yesterday’s Springfield Republican reports on work by geologists at the University of Massachusetts:

The study was authored by David F. Boutt, a hydrogeologist and assistant professor, and Kaitlyn M. Weider, a graduate student in geology…

“More precipitation is falling as rain and less as snow with average annual precipitation displaying a gradual increase of 5 to 10 percent across the Northeast” since the early 1900s, she said…

On average, the water level in the wells rose 1.4 feet over the length of time records were kept, which was more than 20 years at all the wells, Weider said. When the water table is higher and storms occur, water is less likely to be absorbed into the ground and more likely to cause flooding.

“We are expected to receive more frequent and intense precipitation events in the next 50 years,” she said. “I would say more flooded basements are on the way.”

Consider this in light of the condo development proposed for the woods off North Street. [This proposal was approved by the Conservation Commission and the Planning Board in 2009 but is currently on hold pending litigation in Land Court.] Test pit data provided by Kohl Construction (PDF) estimates that the seasonal high water table in several spots is just 16″ below ground, possibly even 14″ in a few cases. Here is a picture of ponding water on the proposed condo site taken this April. This spot is near the end of View Avenue, at a relatively high elevation on the site.
Exacerbating the risk, the condo proposal calls for the removal of numerous large trees, which can lead to groundwater rising (see below). In light of climate trends, it would seem that the margin of safety for the proposed condos is thin and getting thinner.

See also:

Over the past century, according to data from the National Oceanic and Atmospheric Administration, average annual rainfall in the commonwealth has increased from about 36 inches to nearly 50 – a jump of over 33 percent…

…in the last 10 years, an average of over 50 inches of rain has fallen annually in the Valley.

That rainy trend is likely to continue. In a sweeping report on global warming that it issued in June, the U.S. Global Change Research Program, a coalition of scientists and researchers from a dozen federal scientific agencies including NOAA, projects that the Northeast will grow progressively wetter – and warmer – this century. Much of the increasing precipitation could fall in heavy rainstorms that raise the risk of flooding and damage to agriculture, the report says.

Latest Kohl Condo Proposal for North Street: 20 Units as Duplexes (6/18/09)

  • Units 5-12 would be in an area that Conservation Commissioner Paul Wetzel objects to building on because the ground is so wet (March 12 hearing)
  • Wetzel also expressed concerns about how the underground stormwater detention system by Unit 10 would interact with groundwater in and around the wetland
  • Unit 18 appears to be slated for the same place as a unit that Conservation Commissioner Downey Meyer objected to previously as too close to the wetland
  • The total amount of disturbance inside the 100-foot wetlands buffer zone would remain high; Meyer objected to this on the version of the proposal reviewed on March 12…
  • A 1999 Tropical Storm Floyd flood damage report for the end of View Avenue (near proposed Unit 1) suggests much of the site may be at risk of future flooding (View Avenue is at a relatively high elevation on the property)

A single large tree can remove as much as 150 gallons of water from the soil each day. They also intercept a portion of rainfall before it reaches the ground.

[Below, Paul Wetzel refers to an earlier version of the condo proposal which called for 23 units. The current proposal calls for 20 units.]

3:00:22… Commissioner Paul Wetzel: “…I’m just going to say something, we’ve spent a lot of time listening… right now as this plan…I’m inclined to deny it. And its just because…if we were looking at whether this development has an impact on the wetlands, I think it’s going to have an impact on the wetlands. And, I see, a number of things, primarily the underground [detention basin] getting in the way of the hydrology connections underground…”

Watering-up: Studies of Groundwater Rising After Trees Cut (3/9/09)

Research cited below finds that the “sites most susceptible to [hydrology] changes after clearcutting were the transition ones between the bogs or fens and the uplands.” This appears to describe well the land Kohl proposes to remove trees from. An average rise on the order of 20 cm (7.9 inches) in the water table is plausible. This could put unanticipated strains both on the foundations of the condos and on the stormwater mitigation system, a major component of which is underground. In addition, “the clear-cut of riparian and other wetland vegetation may lead to ecosystem conversion, i.e., to the encroachment…of water-tolerant or of shallow-rooted invasive species.” Conservation and Land Use Planner Bruce Young has shown a keen interest in controlling invasive species on Kohl’s land.

The phenomenon of groundwater rising after tree harvests is common enough to have its own term: “watering-up”.