River Crossings: Effects on Wildlife in and Around the Fort River


An illustration of a water inlet

An inlet drop at a culvert's entrance.

When my family moved to Amherst, Massachusetts, I was struck by how many streams and small rivers run through the town. At first I focused on how great it was to have so much nature right where people live, work, and go to school. The waterways are beautiful, and they provide swimming, canoeing, and fishing fun.
Then I noticed how often the local roads cross over the rivers and streams. Almost anywhere I might need to go—school, a friend's house, the grocery store—involved crossing over a stream or river, sometimes several times. I started to wonder how good the mingling of waterways and roadways is for the fish and other wildlife that live here. While it's convenient for people to have these crossings, I had to ask myself, do the crossings allow fish, turtles, salamanders, and other animals to make their way safely along the waterways?


An undersized culvert causing the water flow to contract.

I decided to investigate this question by studying a local waterway. But which one? For insight, I called the Rushing Rivers Institute, a nonprofit river science organization, and spoke by phone with director Dr. Piotr Parasiewicz. He informed me that Amherst's Fort River is a prime habitat for many species, including the endangered bridle shiner fish and the endangered dwarf wedge mussel. Atlantic salmon, American eel, brook trout, sea lampreys, and many other species have also been found in this river, which is one of the longest undammed tributaries of the Connecticut River (the Connecticut River being the largest river in New England). Realizing how ecologically important the Fort River is, I chose it as the subject of my exploration.
I started out by studying a map of the Fort River and saw that there were nine crossings, seven in Amherst and two in neighboring Hadley. Then I visited all the crossings to see how they were made and what shape they were in. I found a variety of structures: bridges, culverts (pipe-like structures), and open-bottom arches (Messmer et al.). Water was flowing through all of them, but I couldn't tell whether fish or other animals would be able to safely use them. I needed to do more background research.


Annie measuring the river depth near a bridge.

Fortunately, I was able to interview the director of the Massachusetts Water Resources Center, Dr. Paula Rees. From Dr. Rees, I learned that my area of interest has a technical term—river and stream continuity—and that there is growing concern about the role of road crossings in disrupting habitats. Organisms in rivers and streams need to move freely so they can access food, shelter, mates, and nesting areas. While a crossing may allow water to flow, it may not be practical for animal movement. Dr. Rees encouraged me to continue my research.

How Crossings Can Hinder Animals 
The scientific articles I read confirmed that most existing crossings were designed to keep the water moving but without much concern about fish and other wildlife (streamcontinuity.org; Jackson et al.). There are many ways in which crossings can prevent or inhibit animal movement.

Annie, 13, a 2008 Young Naturalist Awards essay winner, standing under a bridge, taking notes

Good design features: This bridge spans the riverbank.


For example, a crossing that forces the water to drop at its inlet or outlet can lead to wildlife injuries and make upstream travel impossible (Graber). Culverts that are perched too high, or embedded too little, can make the water flow too shallowly through them; this can be a barrier to all kinds of aquatic life (streamcontinuity.org). Crossings can also collapse as they age, or get clogged with leaves and sticks; beavers love to barricade small crossings when building dams (Walk).
Especially for weaker swimmers, including some amphibians and reptiles, long crossings that don't have riverbank edges as rest areas can be too difficult to navigate (Critter Crossings). Also, animals that live in the streambed can't move through crossings that don't contain natural bedding (Jackson).


Good design features: As these paw prints and bird prints on the enclosed bank show, animals are traveling along [the bridge]

An undersized crossing can contract the water flow, causing increased water speeds and turbulence (Graber). In addition, if a crossing is too narrow or too low, larger animals such as otters or giant salamanders can't enter it (Critter Crossings).

Thinking back to my initial survey of the Fort River crossings, I remembered seeing several of these trouble spots, including beaver activity, outlet drops, and narrowness. Based on what I'd learned from the experts and my reading, I hypothesized that most of the Fort River crossings pose barriers to wildlife.

Good design features: This bridge has good openness, natural bedding, no drops or perches, and it spans the riverbanks.

Refining My Hypothesis 
My next stop was the Environmental Institute at the University of Massachusetts. I met with water ecologist Françoise Walk and learned that several organizations have recently developed the "Massachusetts River and Stream Crossing Standards." In summary, a crossing meets the general standards if:

  • It is wide enough to span one or both banks (at least 1.2 times as wide as the stream).
  • It is open enough (the ratio of cross-sectional area to crossing length is at least 0.25).
  • Water flowing through it is the same depth and speed as the rest of the stream.
  • The bottom is made of the same material as the natural stream bedding.
  • The road above the crossing is accessible to land animals and semi-aquatic animals.

Bad design features: Inlet drop.

Crossings that meet these standards are deemed to be "invisible" to organisms. Substandard crossings are classified as minor, moderate, or severe barriers to movement, depending on how many standards they fail to meet. All new crossings in Massachusetts are required to meet the new standards, but older crossings, such as the Fort River's, are not (Massachusetts River and Stream Crossing Standards).
Now, I refined my hypothesis: Most of the Fort River crossings will not meet the established River and Stream Crossing Standards for the state.

A beaver dam at Fort River crossing.

Bad design features: Physical barriers include beaver dams.

Evaluating the Fort River Crossings 
One chilly autumn afternoon, Françoise and I went to one of the Fort River crossings together, and she showed me how to observe and measure the crossing in order to tell if it met the standards. This involved measuring the crossing itself and observing the water flow (depth and speed). I also examined the road and its surroundings to see if land animals could cross over the road if they needed to. Steep embankments, retaining walls, fences, and heavy traffic would make safe road travel difficult or impossible.
Over the course of the next two weeks, I continued on to the other eight crossings—always wearing my hip-high wading boots so I could get right into the river to measure its depth and look for organisms. I also wore an orange safety vest so I'd be visible while observing the road conditions.


Bad design features: Physical barriers include fallen trees and branches.

My findings for all nine crossings are shown on page 10. Only three of the crossings—all of them bridges—met the general standards. The four other bridges posed moderate to severe barriers to movement due to poor openness ratios, inlet drops and outlet perches, contracted water flow (resulting in turbulence and fast flow), designs that excluded the riverbank edges, beaver dams, fallen trees, and/or road barriers such as retaining walls and fences.

The following photos of the Fort River crossings illustrate some of the differences between acceptable bridge design and substandard bridge design along the Fort River.


Bad design features: Poor openness, crossing doesn't span banks.

The one culvert crossing (actually, a series of four elliptical culverts) was a severe barrier to movement. The culverts had inlet drops, constricted flow, sticks obstructing the inlets, and roadside fencing. The one open-bottom arch crossing (a series of three arches) was also a severe barrier to movement. It had inlet drops, high water speeds, turbulence, and roadway barriers (steep embankments, retaining walls, and fencing).

Based on my research, I concluded that my hypothesis was correct: Most of the Fort River crossings do not meet the established River and Stream Crossing Standards. The most common problems were: low openness ratios (four crossings); inlet drops (four crossings); physical barriers such as beaver dams, stick clogging, lack of banks (four crossings); and barriers to road access (eight crossings).


Bad design features: Heavy traffic and fencing are road-access barriers.


It would be great if all the substandard crossings could be replaced or fixed, but since local and state budgets are being tightened, I don't think that will happen any time soon. Still, I plan to write letters to the town council and the governor asking for the worst barriers to be fixed. Now that I have scientific data to support the request, maybe something can be done.

The most challenging part of my fieldwork was measuring the dimensions of the crossings, which were often long and difficult to reach. The most enjoyable part was going into the river, feeling its energy and seeing the life forms in and around it. I got to spend time at the places where people and nature intersect, and that was an eye-opening experience. I'm really glad I've had the chance to explore nature in this way.


Bad design features: One of the open-bottom arches.

I am left wondering whether the Fort River crossings are similar to the crossings for the other rivers and streams in Amherst. I suspect that most of the others are also substandard. I'd like to test this hypothesis by studying the crossings at some of the other waterways in my area.
I conducted my field study in the autumn, when the rivers and streams in this area are at relatively low flow (Walk). I'm wondering how turbulent and swift the water gets in the narrow crossings during the higher flow times, such as after a summer rainstorm or during the springtime snow melt. I'd like to revisit the Fort River crossings in April or July to check out the situation.


Crossing types, problems, road barriers, and conclusions.

I look forward to continuing my field work in river and stream continuity.


"Critter Crossings: Linking Habitats and Reducing Roadkill." Washington, D.C.: Federal Highway Administration, 2000.
"Evaluating Fish and Wildlife Passage at Culverts and Bridges." Riverways News & Notes 13 (August 2003): 2-4.
Graber, Brian, and Amy Singler. Massachusetts Stream Crossings Handbook. Boston: Commonwealth of Massachusetts, 2005.
Jackson, Scott, et al. Proceedings of the International Conference on Ecology and Transportation. Raleigh, NC: North Carolina State University, 2003.
Massachusetts River and Stream Crossing Standards. Amherst, MA: River and Stream Continuity Partnership, 2006.
Messmer, T., et al. Wildlife and Highways: Seeking Solutions to an Ecological and Socioeconomic Dilemma. Bethesda, MD: The Wildlife Society, 2000.
Parasiewicz, Piotr. Telephone interview by Annie Vernick. Amherst, MA. 17 October 2007.
Rees, Paula. Interviewed by Annie Vernick. Amherst, MA. 26 October 2007.
River and Stream Continuity Project. University of Massachusetts. Retrieved from the World Wide Web on 28 October 2007. http://www.streamcontinuity.org
Walk, Françoise. Interviewed by Annie Vernick. Amherst, MA. 15 November 2007 and 29 November 2007.