Last year on August 28th, Irene blew through Vermont and wreaked havoc in the Connecticut River and Lake Champlain watersheds. The amounts of rain varied but many locations had extended downpours that dropped over 7 inches of rain. Rivers responded to that level of precipitation by increased flow and power that destroyed property and infrastructure that was the wrong size or located in the wrong place. So on the anniversary of the worst flooding in 75 years it is worth pondering about where and why some infrastructure and communities withstood the onslaught of our streams.
Once Irene left, it became clear our roads, culverts, bridges and homes took a beating. The storm washed out or swept away nearly 1,000 culverts and much of the damage to local and state roads was associated with washed out culverts. However, an untold story involves Jenny Coolidge Brook (the Brook). The Brook is a small headwater stream of the West River that flows out of the Green Mountain National Forest. Forest Service roads crisscross the National Forest to allow us access to our wild lands for hiking, bird and wildlife watching, horseback riding and cross-country skiing. The Service owns and maintains the road that crosses over Jenny Coolidge Brook. Where the road crosses the Brook there is a culvert that illuminates a discussion of the value of culverts that mimic nature.
The performance of that culvert in Irene illustrates the difference between what happens when the Service installed a properly sized culvert versus those that are cheaper but “good enough to get by.” The Forest Service estimates that properly sized culverts cost 20 to 40% more at initial construction. They quickly point out that because a properly sized culvert does not clog with debris during storm events they do not have to clean them out as often. Roadways do not wash out when a culvert successfully passes all the high flow caused by events like Irene and since the Forest Service have both properly sized culverts and those from earlier eras that are undersized, they know the difference. It turns out those culverts that are flood hardly cost less in the end than the get-by culverts.
In addition to lower long-term costs, there is a benefit to the stream itself from a properly designed culvert. The Brook culvert is an open-bottomed culvert sized large enough to accommodate extreme flood flow and the bottom of the culvert is natural streambed allowing for the placement of rocks, gravel and boulders inside the culvert. The natural bottom means the flow steps up through pools as opposed to being flat laminar flow forcing fish and other aquatic organisms to navigate the entire length of the culvert with no resting places. In a typical metal get-by culvert with no pools and steps, in most cases it can be impossible for fish and other aquatic organisms to gain upstream passage.
Another telling example of a natural river setting being protective of property during flooding is the difference between what happened in Rutland when the Otter Creek flooded and the same flows just 30 miles downriver in Middlebury. Otter Creek flooded Rutland with almost 19,000 cubic feet per second (CFS) of water on August 28, which is the highest flow ever recorded for that river. The flow in Otter Creek in Middlebury peaked 4 days later at only 7,000 CFS with little flooding or damage.
The answer to why the rush of flood water slowed down with a lower crest in just 30 miles was the intact floodplain between the cities. The land between them is broad, flat, has extensive wetlands and is for the most part undeveloped. The floodwaters spilled over into the floodplain as nature intended and only gradually did the floodplain release water back into the river and then past Middlebury.
So on this, the anniversary of Irene, one has to consider more than river situations where undisturbed or mimicked natural dynamics provided positive results to flooding. You have to look at the effects Irene had on the people of Vermont. One perspective on our future after Irene starts with musings about the strong force. The strong force is one of the four basic forces in nature. It holds together the essential particles that make up all matter in the universe, and it is virtually impossible to overcome the strong force. As you use more energy to try to separate the building blocks of atoms, the strong force becomes more powerful. Vermonters are like the strong force. Here in Vermont the flooding brought out the strength of Vermonters to cope with the flooding itself, and then deal with the after effects of Irene and like the strong force, nothing will deter us from rebuilding our future. Our unity only grows stronger as the difficulty rises.
David L. Deen is River Steward for the Connecticut River Watershed Council. CRC is celebrating 60 years as a protector of the Connecticut River.