culvert

Typical culvert for a small brook – note the waterfall at the end of the culvert.

We call them dirt roads, but these days, most are made of gravel. Tourists tend to drive around Vermont on paved roads like Route 2, or Route 5. The really adventurous might head down the Peacham Danville Road or up the Bruce Badger Memorial Highway. There are even a few local residents who live on pavement and seldom leave it. But most of us spend a lot time on gravel. We get to complain about potholes, washboards, and the gullies that appear after hard thundershowers.

Local roads in Vermont come in several flavors. Class 1 roads are state highways, paid for and maintained by the state of Vermont. Class 2 roads are paid for and maintained by towns and are main connecting roads like the Peacham Danville Road. They are almost all paved. The large majority of gravel roads that we encounter are Class 3. They are plowed in winter and maintained regularly in summer. Class 4 roads are often still dirt, without much gravel, and can be rough and muddy. Towns are not required to plow class 4 roads and can set their own maintenance standards. The lowest classification of a town road is a “legal trail.” Towns have no obligation to do anything at all on a legal trail, but they remain a public right of way.

There is a huge variation in the mileage of roads in Vermont towns. Statewide, there are about as many paved roads as gravel roads, but like so many average statistics, the numbers are skewed by Chittenden County. Over there, they have 901 miles of pavement and 261 miles of gravel. Williston has 83 miles of pavement and 9 miles of gravel and dirt. Here in the Northeast Kingdom, gravel is the surface of choice (or necessity). Caledonia County has 440 miles of pavement and 623 miles of gravel, with by far the highest percentage of gravel roads of the counties in Vermont. Stannard has 18 miles of town highways, none of them paved. Peacham has 71 miles of town highways, 61 of which are gravel or “graded dirt.” Danville has 121 miles of town highways, 106 of which are gravel or dirt. Danville has the distinction of having the most miles of town highway in the state.

Maintaining gravel roads is an art as much as a science. Road foremen have a lot of factors to balance. The ideal candidate needs to be patient and a skilled diplomat, while having a knack for maintaining equipment, a sound understanding of the road structure, familiarity with stormwater runoff, and the ability to manage a crew of workers. There’s no question they have the most important job in town. Taxpayers want to spend as little as possible while being able to drive on roads that are smooth and dry. Residents complain that their road hasn’t been graded, or that the grader left a mess cleaning out a turnout, or that the dust is terrible. As soon as the road has been made smooth, residents complain that the cars drive too fast. On and on.

The everyday challenges of washboards and potholes pale in comparison to the damage wrought by hard thunderstorms. The year 2011 is remembered statewide for Tropical Storm Irene in August of that year, but on the evening of May 26th, 2011, a dangerous thunderstorm blew through southern Caledonia County. My wife Betsy was at a friend’s house and I was home listening to the Red Sox game when the warning beeps came over the radio. A bad storm was rolling our way from Barre and a funnel cloud had been sighted. We were advised to take shelter immediately. It was very ominous, as were the wind and clouds that soon enveloped us. When it cut loose, I knew our roads were in for a serious test. Betsy made her way home, later finding out that she had passed through East Peacham just before the road blew out, leaving a 10-foot deep crater. By about ten o’clock, the storm had dumped over five inches of rain. Almost every gravel road in town suffered serious damage and several were cut when culverts were overwhelmed. In Peacham, it cost us several hundred thousand dollars and about two years to put it all back together.

As it happened, the legislature had recently passed Act 110, which revised town road and bridge standards. Towns were first incentivized to adopt standards in 1999, at the urging of FEMA. It seems the agency was tired of sending money to fix the same problems they had paid to fix a few years before. In 2010 the legislature also recognized the water quality problems being caused by frequent washouts and adopted best management practices (BMPs). In 2013 the standards were updated to include the state’s Stream Alteration Standard, including the sizing of culverts and the construction of ditches.

Resilience is a popular word these days as we contemplate climate change. For local taxpayers, making our gravel roads resilient to major storms should be a no-brainer. The most obvious step is to make sure culverts are big enough, not just for the everyday couple of inches of rain, but for the big events such as we saw in 2011. The state has been pushing this for a number of years and most towns are working on upgrading their culverts, of which there are many. The culvert at the end of your driveway could be the key to your escaping major personal damage in the next heavy rain, and the culvert down the road could be the key to the town escaping another costly road repair.

There can be multiple benefits from increasing the size of culverts. The obvious one is to accommodate a five-inch thunderstorm. Culverts are sized by engineers by taking into account the watershed that is feeding water to it. The steepness of the terrain, the type of vegetation, and the presence of any flat flood storage areas are three key factors. The culvert itself will have a length and a slope which will affect how much water can pass through it. Knowing all these factors, the engineer must then decide how much rain to plan for. Before 2013, the standard was the peak rainfall you could statistically expect every 25 years. That statistic has risen dramatically over the past 25 years. Now the state standards for sizing culverts are more nuanced to take into account the wide variations in runoff from a given amount of rain in a given amount of time in a given place.

Another major factor driving culvert design is the desire to allow fish to swim up or down through the culvert. This is known as fish passage. Along actual brooks, round culverts often represent barriers to fish. Sometimes they are too steep for fish to swim up, or they have a drop off at the outlet end of the pipe that is too high for a fish to jump into the pipe. The state offers incentives to towns willing to install concrete box culverts for perennial streams. These structures are pre-cast and usually about 5 feet square. The bottom is shaped to allow for stream gravel to accumulate, resulting in a continuation of the natural streambed right through the culvert.

Next month I’ll get into the anatomy of a gravel road and the mechanics of how they are (or could be) maintained to provide a reliable driving surface while also keeping the gravel on the road instead of eroding into streams.