Future modeling by scientists indicates that heat waves the likes of which eastern North America experienced every 20 years will be occurring between a year to every six years in the latter half of this century, he said. New York State is predicted to have the climate of South Carolina by the end of the century.
By then, what was once a 20-year daily rain storm will happen every four to 18 years — a big range of uncertainty, Frei acknowledged. “For this area, we’re talking about a 3 to 5 degree average temperature increase in the latter half of the century and a five-to-nine-degree increase by the end of century,” he said. More evaporation due to the warmer temperature means that even though there may be more rain, less water will fall into local waterways. “Spring runoff may not exist by the end of the century…this will have a big impact on stream ecology and water quality.”
Frei said most hydrology models used for infrastructure planning assume a stationary pattern, but the latest research shows this is a dangerous misconception. And he noted that since 1990, governments around the world have been justifying their use of satellite data as a reason to reduce their meteorological stations — a distressing trend, given that such data was never more needed for future planning.
Allowing a river to run its course
Roy Schiff, based in Vermont, noted that his state had assessed over 1350 miles of stream channels to determine how natural processes have been modified by channel management activities, corridor encroachments and land use/land cover changes. Recognizing the need to protect steam ecosystems as well as protect the public from destructive floods, Vermont is devising new river management guidelines that involve protecting and purchasing conservation easements within river corridors in order to enable streams to run their course. In the past, management has relied on building buffers instead.
Schiff noted that the nation has a history “of armoring rivers.” In Vermont, 176 miles of rivers have been straightened, and following Irene, 77 miles of rivers were dredged. Unfortunately, the pattern of settlement in the floodplain has resulted in many people living and working in the spots most vulnerable to flooding, he said.
The old ways of doing things have not worked long-term. Dredging, for example, said Schiff, “… is not cost-effective and has a huge impact on water quality.”
Why? “The dredged area will migrate downstream, cut down the channel, and destabilizes a major area downstream,” explained Schiff. “Rivers sort material naturally, with boulders armoring the bottom of the bed and cobble beds created. If you start digging and cut through this layer, you will initiate a process to change that water channel for a long time. River management was all about water, but now it’s all about sediment and debris.”
Early management strategies didn’t acknowledge the natural dynamics of rivers and streams — “that they cut down, widen out, fill and reconnect old floodplains.” Schiff said three-quarters of Vermont’s 26,000 miles of rivers consist of streams that are in the cutting-down and widening stage of their evolution. Armoring such rivers to protect nearby infrastructure doesn’t change the process. Despite the considerable financial commitment, the risk remains, said Schiff.
Schiff said his firm is currently working on river corridor planning that allows the river run its course. The width of the corridor is establishing by measuring the amplitude of its meandering and varies depending on the type of stream; maps showing the inundation and erosion patterns help predict where the river might migrate to in the future. In Vermont, 22 communities have adopted zoning codes that protect fluvial erosion hazard corridors. So far, conserving river corridors has been a grassroots municipal movement, but Schiff suspects it will soon become a state policy.
Following the flooding of New Orleans by Katrina, FEMA contracted a study to provide a benefit-cost analysis of protected river corridors and floodplains. It found the benefits were not just aesthetic. Air quality also improved air quality. Biological control, climate regulation, and erosion control were also helped. The estimated benefits were calculated at $37,493 per acre per year, compared with $7853 per acre year for green open space. “Functionary flood plains have a huge economic value,” Schiff argued. His firm is working on a study that examines this approach at the local level.
“It’s almost impossible to understand what’s going on a project site if you don’t know the larger context,” Schiff concluded. “If you’re managing sites over and over again, it’s an invitation to step back and understand the broader context. Every community and neighborhood should have a river corridor plan.”
The all-day event also featured several afternoon sessions for attending municipal officials, residents and business owners.
