Levin: Flashflood Mitigation

Jul 12, 2017

The flow from the July 1st downpour had jumped two streambeds and overwhelmed two culverts, trisecting Thetford’s Five Corners Road into three unequal lengths, scouring out a pair of nearly forty-foot wide spillways into the woods. It had left skirts of debris fixed to tree trunks and draped from low limbs, some more than a foot above the ground.

I’d missed the storm. By the time I returned home, our town road crew had already repaired both culverts temporarily. But beyond the road, the flashflood had leveled great swaths of grasses, ferns, and small shrubs, all of which now lay flat, aligned with the western direction of flow. Outside the immediate flood zone, however, apart from the ground still resembling a waterlogged sponge, the woods appeared normal.

Charlie Hohn, a wetlands ecologist with the Vermont Department of Environmental Conservation, travels the state to monitor wetlands, those landscapes midway between upland and aquatic ecosystems.

They’re characterized by saturation during the growing season that promotes the growth of plants favored by standing water and the development of an underlayment of hydric soils. Broad categories of wetlands include swamps, marshes, and peatlands. And when Hohn visits a wetland he takes time to discuss with the respective landowners the unequivocal importance of their property to the integrity of wild Vermont, which includes mitigating the impact of floods.

A few days after the storm, Hohn visited Coyote Hollow, our neighboring wetland, to assess conditions there. He called it a very healthy intermediate fen, and was enthusiastic about the beneficial effect it had had on the flashfloods.

The flooded streams had scoured out their beds down to the Earth’s bare bones, exposing rocks and stones that likely hadn’t seen daylight since the Ice Age. But at the edge of the fen, the water slowed and pooled, and according to Hohn had softened the downstream impact of the deluge. The only remaining evidence of the flood was that a patina of silt that reached nearly a foot up their stalks covered sedges and irises.

Of course, I had to see this for myself — and not fifty feet into the fen, except for the still saturated soil, I found that, like a Penn and Teller trick writ large, any visible sign of the flood had indeed vanished.