Why Streams Flood—And What We Can Do About It

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“We’re fighting against a process we haven’t dealt with much before: a valley reforming process. I’m proposing we need to have a different response in recovery.” – Mike Kline

Mike Kline, retired State Rivers Program Manager and WEC member from the Bear Swamp area of Middlesex, was the Annual Meeting’s featured speaker. He discussed flooding causes and potential mitigation strategies, drawing from past flood events and stream management practices in Vermont.

Kline pointed out WEC is a “headwater utility,” with a service area of steep, narrow valleys in the upland headwaters of seven major Vermont watersheds. Reflecting on flood events over the last 15 years, from Tropical Storm Irene to the consecutive July 10 storms in 2023 and 2024, Kline described the emotional experience of a flood like a bereavement: shock, overwhelm, heartbreak. Flood damage to private property and public property and infrastructure is hard to bear, and expensive to fix. Rebuild infrastructure in more or less the same mold and in the same location, and the next flood will wash it away. Kline proposed breaking this cycle by reconsidering the space streams and rivers need for floodplain and water storage.

Over the course of human history, people have put enormous effort and energy into straightening and channeling waterways in order to keep that water from inundating the surrounding land. But as Kline pointed out, that channeling creates fast, powerful water that in a flood is capable of increasingly damaging erosion, landslides, and infrastructure damage. A meandering stream, within a corridor that gives the stream plenty of room to oxbow and spill over the land, is far less erosive.

Kline discussed the historical preference for straight, channeled streams rather than meandering ones, tracing this approach back to early New England settlement. “If you didn’t like the way your neighbor was ditching their land,” he said, “you could go and do it for them.” 

Coarse sediment acts like speed bumps in river systems, Kline said. Preserving that sediment, he said, is a cost-effective method for preventing stream erosion and bank failure. But whereas a meandering stream can move coarse gravel, “a particle the size of a baseball,” a channel can move “a boulder the size of this lectern,” stripping sediment from streambeds and depositing it downstream in unwanted locations. 

In glacial lake areas with fine silt soils, like many of Vermont’s valleys, Kline explained that water can “down-cut” the streambed, or force its way deeper, in high-velocity flow or when flow is obstructed. He said channeling streams encourages this down-cutting process, and that once a stream down-cuts, it becomes more erosive and no longer accesses its own floodplain.

Kline pulled examples from local streams and roads particularly impacted by recent flooding, especially Great Brook and Great Brook Road in Middlesex. Three factors contribute to a stream’s erosive power, said Kline: depth, slope, and roughness. All three of these stream characteristics have been intensified by historic decisions made “in the honest intent to reduce inundation of our land,” but noted that during flood events, it makes inundation more severe, less predictable, and more harmful.

 “We’re fighting against a process we haven’t dealt with much before: a valley reforming process,” and added, “I’m proposing we need to have a different response in recovery.”

A key shift in thinking, Kline explained, was considering flooding within the context of the whole watershed. “All efforts to protect one section of stream will have effects downriver,” he said. Just like WEC members on rural hillsides are impacted by flood damage in villages and downtown areas, where they may work and shop and recreate, efforts to protect village or downtown areas will impact river systems up- and downstream. 

Among the approaches he described were: limiting new development in valley areas, giving streams time and space to “re-armor” themselves with sediment and debris, restoring floodplains and wooded buffers, preparing debris management plans, and working with private landowners to create corridor easements.

To build a corridor easement costs in the $50,000 range, Kline said, as opposed to the “$2.5 million for Middlesex to put its road back together.”

Kline concluded with an image of a flooded floodplain, a wet valley, but with no infrastructure or infrastructure damage in sight.

Goddard Graves asked Kline how to get his message to the people responsible for repair. There’s a program called Rivers and Roads, designed for road crews, who are usually the first on the scene after water recedes, Kline responded. “Mostly, we get their hands dirty,” he said. They run models of different road rebuilds and crank water to see how flooding would impact each design. Approximately 600 road workers have taken the two-day course.

Angela Manning commented that in her experience, flooding exposed properties to other forms of damage; and Lindy Biggs asked if Vermont had a program for paying landowners for ecosystem services to their community. Kline pounced on this concept: paying for that service is something we should consider, he said: “We don’t think about the service landowners give us all when they allow their land to flood—especially if it’s going to flood anyway.”