ABOUT THE AUTHOR
Curtis C. Bohlen is director of the Casco Bay Estuary Partnership at USM's Muskie School.
Most people only notice culverts when something goes wrong. A house flooded, or a road damaged, and suddenly, the humble culvert matters.
Several weeks ago, on Aug. 8, more than 5 inches of rain fell in Yarmouth and nearby towns in a 24-hour period. Rain fell at a rate of almost 1 inch per hour for two hours and at a half-inch per hour for most of four hours.
It was quite a storm. Intense rain falling on an already soggy landscape led to flooding.
Road culverts in nearby towns were overwhelmed. Roads were damaged; some were closed. Local road crews are now stuck cleaning up the mess, replacing damaged culverts and making needed repairs. The state has applied for disaster funding to help fund these repairs.
Replacing a culvert may appear to be a routine matter, and indeed it often is routine. But today it also offers insight into what it means to live in a greenhouse world.
Culverts do their job in the context of a particular pattern of rainfall and stream flow. Their useful life typically spans decades. Culverts installed today to replace the ones damaged a few weeks ago will remain in service into the middle of the century, when scientists project Maine's climate will be quite different from today.
Total annual precipitation in Portland has increased 20 percent over the past 150 years. Climate modelers predict that Maine will see further increases in coming years.
Precipitation will come, on average, in more intense storms. No detailed studies have been carried out for the Casco Bay region. But if predictions here are similar to what has been learned in New Hampshire and Massachusetts, we might see a storm like the Aug. 8 deluge every few years.
We do not want to be replacing culverts every few years. Simple prudence suggests we not only replace damaged culverts, but enlarge them or replace them with bridges.
Larger culverts cost a bit more, and bridges cost more still, but they would better survive the more intense storms of the future, reducing repair costs and saving tax dollars.
Larger culverts and bridges also offer environmental benefits. Undersized culverts not only put roads at risk, they create a barrier to movement of aquatic organisms.
Larger culverts are more likely to permit upstream passage of sea-run fish like salmon and alewives. Open bottom culverts and bridge spans have the added benefit of not disrupting the bottom substrate.
A survey of road crossings in the lower Penobscot basin found that over half the culverts presented a severe barrier to movement of fish.
River advocates statewide have begun replacing undersized culverts with larger structures purely because of the fisheries benefits.
Replacing failed culverts with larger ones would protect public investment in the face of anticipated climate change and provide environmental benefits. But it is uncommon, due to several practical and policy barriers.
Few people – even professionals working in the field – are aware of just how profoundly Maine's climate has changed over the past 100 years, much less how much it is expected to change in the next 50.
We need to reach key people making infrastructure design and investment decisions – from road crews to foresters, from subdivision designers to town councils – so that they consider climate change in their thinking.
The size of most culverts and road crossings today is based on historic precipitation and stream flow records. The past, however, is no longer a reliable indicator of the future.
Without good data on future conditions, it is impossible to design and may be difficult to justify the costs of, a larger culvert. We need to develop and make available predictions based on the best available science about future climate and stream flow on local (town) and regional (Casco Bay watershed) scales.
When considering culvert upgrades, a word of caution is needed. By restricting water flow, undersized culverts may actually be reducing erosion or flooding downstream.
Regulatory review ensures such potential impacts are evaluated. Maine's Department of Environmental Protection already exempts most replacement culverts from state review (provided they are not too long) even if the replacement culvert is larger in diameter.
We need to ensure that local decision-makers are aware of and take advantage of this regulatory flexibility.
We are just beginning to recognize the challenges of living with a changing climate. The humble culvert offers an object lesson about decisions we will face with increasing frequency.
Society-wide, we need to heed these lessons and learn to plan (and to invest time and resources) with climate change in mind.
In our sister state of New Hampshire, the city of Keene has developed and is putting into practice a climate change adaptation plan, including cost-benefit assessment of replacing culverts that are likely to fail in a changing climate.
Here in the Casco Bay region, we need the best possible science and creative thinking from town officials, lawmakers and regulators to help us mitigate and adapt to the effects of climate change on all of us.
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