Millions of Dollars of Property Outside the Official Floodplain Vulnerable to Localized Flooding

As reported in today’s Sunday Republican, the Pioneer Valley Planning Commission invites the public to review a Local Natural Hazards Mitigation Plan for Northampton (PDF) as well as plans for other valley municipalities.

We believe Northampton’s proposed wetlands ordinance, by inviting developers to encroach as close as 10 feet to wetlands in our more populous districts, goes against the goals of PVPC’s plan. We encourage the public to express their concerns to Andrew Smith at the Commission, 413-781-6045,

We’d like to call particular attention to the following passages from PVPC’s plan addressing flooding. Certain neighborhoods in Northampton have a special interest in preserving the drainage capacities of our urban wetlands:

Localized Flooding

During the Natural Hazard Mitigation Committee’s meetings, several points in town were identified as areas that flood frequently but are outside of the community’s Flood Insurance Rate Map boundaries. These areas are, roughly:

  • The Intersection of State Street / Stoddard Street / Perkins Avenue to Route 5 & 10. This neighborhood is medium density residential. Approximately eighteen could be affected by a flood incident. 100% damage to 100% of the structures, estimated cost of repairing or replacing to be $4,860,000.

  • The area surrounding Riverside Drive, Nutting Avenue, Ormond Street, Federal Street. Approximately sixty-eight could be affected by a flood incident. At 100% damage to 100% of the structures, the estimated cost of repairing or replacing would be $18,360,000.

  • Pomeroy Terrace/Eastern Avenue. This a low-density residential / light commercial section of town that could flood from a collapsed drainage pipe. Approximately 15 structures could be affected, and at 100% damage to 100% of the structures, the estimated cost would be $4,050,000.

…The Comprehensive Emergency Management (CEM) Plan for Northampton lists the following generic mitigation measures for flood planning… Strict adherence should be paid to land use and building codes, and new construction should not be built in flood-prone areas… Natural water storage areas should be preserved. (p.34)

…The City of Northampton has adopted several land use regulations that serve to limit or regulate development in floodplains, to manage stormwater runoff, and to protect groundwater and wetland resources, the latter of which often provide important flood storage capacity. These regulations are summarized below and their effectiveness evaluated in Table 4-1. (p.36)

…Drainage systems, including detention, retention, and infiltration, must be designed to prevent any increase in peak flows for the one (1) or two (2), ten (10), and one-hundred (100) year Soil Conservation Service design storms. TR-55 (or TR-20 with all inputs and outputs shown) should be used for calculating drainage systems. In addition, drainage systems should include water quality/settling basins that detain the stormwater draining off the site in a 4/10 inch rain storm for an average of at least six hours. (Amended April 11, 1991) …All subdivision proposals and other proposed new development shall be reviewed to determine whether such proposals will be reasonably safe from flooding…(p.38)

The City of Northampton has established a set of bylaws designed in part to “lessen congestion in the streets; to conserve health; to secure safety from fire, flood, panic, and other dangers; to provide adequate light and air; to prevent overcrowding of land; to avoid undue concentration of population; to encourage housing for persons of all income levels; to facilitate the adequate provision of transportation, water, water supply, drainage, sewerage, schools, parks, open space and other public requirements; to conserve the value of land and buildings, including the conservation of natural resources and the prevention of blight and pollution of the environment; to encourage the most appropriate use of land through-out the City, including consideration of the recommendations of the City’s master plan, adopted by the Planning Board, and the comprehensive plan of the Pioneer Valley Regional Planning Commission; and to preserve and increase amenities by the promulgation of regulations to fulfill said objectives.” (p.39)

…Major projects, except in the Central Business District must be designed so there is no increase in peak flows from the one (1) or two (2) and ten (10) year Soil Conservation Service design storm from pre-development conditions (the condition at the time a site plan approval is requested) and so that the runoff from a 4/10 inch rain storm (first flush) is detained on site for an average of six hours. These requirements shall not apply if the project will discharge into a City storm drain system that the Planning Board finds can accommodate the expected discharge with no adverse impacts. (p.41)

See also:

Northampton’s Flood and Natural Hazard Mitigation Plan: Floyd Flood Damage Reported Behind View Avenue; Avoid Building on Filled Wetlands [emphasis added]
Northampton can experience flooding in any part of the City. One great misunderstanding is the belief that floods only happen in the floodplain. With sufficient rain, almost any area will experience at least pockets of surface flooding or overland flooding. Overland flooding in rural areas can result in erosion, washouts, road damage, loss of crops and septic system back-ups. Heavy rain in the more urbanized parts of the City with extensive paved and impervious surfaces can easily overwhelm stormwater facilities resulting in localized flooding and basement damage. Stormwater flooding also contributes to water pollution by carrying silt, oil, fertilizers, pesticides and waste into streams, rivers and lakes. As the intensity of development continues to increase, Northampton will see a corresponding increase in serious stormwater problems. It is therefore important that the City as a whole, not just residents of the identified floodplain, address the need for mitigation. Flood and hazard mitigation is any preventive actions a community can take to reduce risks to people and property and minimize damage to structures, infrastructure and other resources from flood or other hazardous events. Hazard mitigation and loss prevention is not the same thing as emergency response. Some flood loss reduction can be achieved by components of response plans and preparedness plans, such as a flood warning system or a plan to evacuate flood prone areas. However, warning and evacuation deal only with the immediate needs during and following a flood event. Hazard mitigation is much more effective when it is directed toward reducing the need to respond to emergencies, by lessening the impact of the hazard ahead of time. (Massachusetts Department of Environmental Management 1997, 3)

…In a table of Existing Mitigation Strategies, the plan includes a “100 foot buffer around wetlands and the wetland resource area itself…” It says this strategy has been “Effective”, and says that an option to improve it would be to “Strengthen Wetland Ordinance”…

Flooding is already affecting Northampton’s built-up areas during major storms. Weakening wetlands buffer zone requirements downtown will make this worse

Northampton Open Space Plan: “This loss of habitat and natural flood buffering areas is Northampton’s most serious environmental problem”

Alex Ghiselin, Letter to Gazette: “Don’t let development encroach on our wetlands”
The failure of the storm water system built as a part of the Northampton High School renovation six years ago illustrates why protecting wetlands is so important. Silt has filled the retention pond so there is no capacity to slow a storm surge which now flows unimpeded into the Mill River and contributes to flooding downstream. This accumulated silt also raised the water table and spills ground water into nearby basements…

Without maintenance, these [storm water mitigation] systems are part of the problem, not the solution…

Wetlands do not need to be maintained; they just need to be protected.

Flooding Around Barrett Street Marsh: Development Eyed as Factor
…The city has been sued over problems in the marsh and has a responsibility to maintain the area’s water infrastructure as part of a mediated agreement involving neighborhood residents…

Ward 1 City Councilor Maureen T. Carney, said residents around the marsh are anxious about the potential for flooding, particularly on Church Street, which was subject to heavy flooding and property damage years ago…

Several city residents are protesting the city’s actions and calling for public hearings. Some say the city has created the problem by the way it has allowed the area to develop.

“I suspect water problems will persist long after the beavers move on,” said Joanne Montgomery, a former Conservation Commission member, as she addressed the council Thursday.

Connecticut River Watershed Action Plan: Remove impervious surfaces within 50 feet of streams
To reduce nonpoint source pollution from stormwater runoff, the Connecticut River Strategic Plan proposes the removal of impervious surfaces within 50 feet of streams and the investigation of “functional replacements” (such as the use of permeable pavement) for impervious surfaces within 100 feet of streams, in developed areas (PVPC, 2001). In the urbanized areas, the removal or retrofitting of impervious areas and the implementation of Stormwater Best Management Practices (BMPs) could be beneficial in improving water quality. The interception and redirection of stormwater, that would otherwise enter storm drains and CSOs, would contribute to the reduction of peak flow during heavy storms. One example is to collect runoff from roofs for use in lawn irrigation.

…Areas with high percentages of impervious surfaces are most likely to be affected by increase stormwater runoff into rivers and streams. (p.46)

EPA: Wetlands and Flood Protection
Wetlands within and downstream of urban areas are particularly valuable, counteracting the greatly increased rate and volume of surface-water runoff from pavement and buildings…

The Economic Value of Wetlands: Wetlands’ Role in Flood Protection in Western Washington