Flood Resiliency in Bennington
A town-state partnership to begin avoiding hazards*
The Roaring Branch is a tributary to the Walloomsac River which flows in Woodford and Bennington, Vermont. It becomes a tremendously dynamic and powerful force at times of flood, delivering an astounding volume of boulder, cobble and woody debris into the urbanized area of Bennington. For 150 years or more, this municipality and its residents have struggled with the river, attempting to confine and control it with a system of earthen berms and structural levees.
The Roaring Branch has won most of the contests. It has catastrophically breached the berms, inundating residential and industrial areas, and devastating public infrastructure including roads and bridges. History shows that damaging events take place about every 20 years on the Roaring Branch, and each flood triggers a reaction by the village to re-dredge the channel and reconstruct the gravel berms. The results has left the “protected” property and infrastructure behind the berms extremely vulnerable to the next flood.
After years of disagreement between the Town and State on how to manage the river and its riparian lands—with one dispute going all the way to the Vermont Supreme Court—Bennington reached out for assistance. In 2008, the Town formed a partnership with the Vermont Department of Environmental Conservation (DEC) to find ways of reducing flood and erosion hazards associated with the Roaring Branch. It was agreed that State investments to protect public infrastructure within the river corridor were needed and that these would likely include management practices within the river itself. But for the State’s part, these investments only became prudent if the Town passed bylaws to limit further encroachment to the river. This agreement was seminal to the definition of a State river corridor incentives program (later codified in Act 110), where commitment to manage an urban river gave incentive to a community to take an avoidance approach to riparian land use.
State Ecosystem Restoration Grants were made to the Town to complete stream geomorphic assessments and a river corridor plan, which provided detailed hazard mitigation options for restoring the river and protecting the community. The DEC Rivers Program (VRP) developed a model ordinance and provided technical assistance throughout the town’s process to adopt a fluvial erosion hazard (FEH) area which would limit development within the river corridor. In response to the town adoption of the FEH bylaws, the VRP found funding to design and construct part of a major floodplain restoration project to re-connect historic floodplain areas to the channel on recently acquired town land. The objectives were to lower inundation levels, reduce flood velocities, and create space away from existing infrastructure for sediment deposition between the Brooklyn and Park Street Bridges.
Project construction began in 2010, and approximately 1,400 feet of the 3,500-foot project was constructed. Berms immediately adjacent the channel were removed and a new armored berm was constructed on the back side of the retored floodplain. This project stopped the trend of confining the Roaring Branch and begins opening the channel and floodplain up as much as possible to reduce flood and erosion risks.
Although only a portion of the proposed floodplain reconnection had taken place when Tropical Storm Irene hit, the partially expanded floodplain likely helped save the Park Street Bridge. The storm produced the flood of record (~Q100) and moved large amounts of sediment and woody debris. Approximately 500,000 cubic yards (over 35,000 dump truck loads) of sediment was deposited in 3.5 miles of the Roaring Branch in Bennington. There was damage: bridges were filled with sediment, a portion of the Town water main was destroyed, houses and garages were washed way, many banks were eroded, and flood protection levees were undermined.
Portions of the remaining berms that were proposed for removal during the floodplain restoration project were washed out during the flood exposing large areas of Bennington to increased flood risks. Convinced they were on the right track, town officials made the decision to complete the floodplain restoration project as part of the flood recovery work. The town needed to dredge the channels that had filled within the city, and decided to use the materials to continue building the new floodplain and berm at the back of the floodplain rather than windrow a berm along the channel edge. Constructing the remainder of the floodplain restoration project, and extending it further, also reduced the cost of the flood recovery effort as the area behind the proposed berm is being used as a local fill deposit area to minimize haul distance for sediment excavation from the channel. The DEC was making grants from its 2011 Ecosystem Restoration capital funds during the recovery, and showed its continued commitment to Bennington by awarding another grant to pay for armoring the new berm. The state funding source places a priority on making grants to communities that have adopted river corridor and shoreland zoning bylaws.
Although dealing with a multi-million dollar flood recovery effort to limit future flood and erosion risks following Irene with no clear funding assistance available, the Town of Bennington remains committed to river corridor protection. Moving forward with and contributing to the final phases of the floodplain restoration project, maintaining implementation of the adopted fluvial erosion hazard zone, preserving the widened floodplain where possible, and only armoring those areas where public safety and infrastructure are at risk exemplify a consistent goal of river corridor improvement and protection. This approach demonstrated a science-based approach and a continuing State-Town partnership in river corridor protection and flood resiliency that serves as a model for other Vermont municipalities. The DEC looks forward to working with sister agencies and the legislature to strengthen a State incentives program that will help municipalities avoid and mitigate flood hazards through river corridor protections.
*This report was prepared by Mike Kline (DEC Rivers Program Manager) and Roy Schiff (River Restoration Engineer with Bennington’s project consultants Milone and MacBroom, Inc.)