Hazard areas highlighted in Ammonoosuc River report
November 10, 2010
CARROLL — "There's a grave situation at the two snow-making ponds at the Bretton Woods Ski Area." Those were the words of plained fluvial geomorphologist Nicolas Miller of Field Geology Services of Farmington, Me., on Thursday evening in front of the Planning Board and Conservation Commission in Twin Mountain.
The scientist used a slide talk to report on some of the data-collection work done on the Ammonoosuc River over the last two years. The data collection was performed under the aegis of Planning Director Tara Bamford of the North Country Council and John Field, Ph.D., principal of the company that bears his name.
There is a 15- to 20-foot drop in the unconsolidated gravels and sands near the ponds that, if flooded, could compromise the Ski Area buildings and adjacent real estate, Mr. Miller said.
As he pointed to an aerial photo depicting the ponds, west of Route 302, whose depths he said he had not researched, he noted, "This is kinda scary," calling it a "red flag" situation.
If the ponds were to be overtopped by water overflowing the banks of the Ammonoosuc River, sediments would be rapidly sent downstream.
The data collection project will result in fluvial erosion hazard maps, divided into "reaches," each of which is about a mile long.
Over the years, the Ammonoosuc River, like most New England rivers, has been confined by structures, such as bridges and riprap, and straightened for log drives and railroad building, Mr. Miller explained. Straightened rivers have steeper riverbeds, and water flowing downstream moves more quickly and has more "energy" to release.
Mr. Miller spoke of the river as though it were a person, pointing out, for example, that it "wants" to meander.
The Ammonoosuc River has no "extreme" zones in Carroll, but the reach alongside the Presidential golf course at the Mount Washington Hotel is rated a "very high hazard" zone.
Most other reaches are rated as "high" hazards.
The Lower Falls area where the river flows over bedrock in the White Mountain National Forest is rated geologically as a "very low hazard" area.
Large sandbars, some dotted with large cobbles, characterize the points at which both the Zealand and Little Rivers join the Ammonoosuc.
The final report from Field Geology Services has been delayed until Feb. 2011, according to Ms. Bamford, but those field observations of particular interest to the state Department of Transportation will be forwarded to state engineers.
"We expect the completed report to contain recommendations about not only prevention of further problems, but also restoration of some segments of the river to reduce current chronic problem areas," Ms. Bamford said in an e-mail exchange. "One such restoration project is already being explored as a
prototype in Lisbon."
She added that she would work with the Ammonoosuc River Local Advisory Committee (LAC) and the Ammonoosuc Conservation Trust (ACT), and NCC's Transportation Advisory Committee to help see that some restoration projects are implemented. Changes could be also implemented by working with NCC's Transportation Advisory Committee, Ms. Bamford noted, that could save taxpayers' dollars over time by avoiding damage to Rte. 302 and possibly to abutments and other supporting members of bridges that span the river.
The entire Ammonoosuc River from its headwaters at the Lakes of the Clouds to the Connecticut River is in the New Hampshire
Rivers Management and Protection Program (RMPP).
The maps shown at Thursday evening's presentation are available for study in the town offices.
Dr. Field's website (www.field-geology.com) points out that "geological studies can provide important information on the location, magnitude and frequency of various flood hazards, such as floodplain inundation, bank erosion, and channel avulsions. A comprehensive understanding of potential hazards is essential for communities that are developing flood mitigation plans and struggling with land use issues.
Planning Board vice chairman Dr. Evan Karpf said the Board would look into whether or not any additional ordinances should be presented to townspeople for possible adoption, based on new data and information.