Wetland Culverts in Fayette County

Pennsylvania has the highest density of waterways of any state in the country[1]. The commonwealth also has one of the largest networks of roads in the nation[2]. This means that Pennsylvania has an incredible number of bridges to bring these roadways over our many waterways. Pennsylvania is currently home to over 25,000 state-owned bridges – the third highest number in the nation. The way in which those bridges, and their associated approaching roads’ underpasses and culverts, can either be a help–or a hindrance–to wildlife movement. At the same time, this infrastructure is aging, with an average age of a Pennsylvania bridge being over 50 years old[3], meaning that many are reaching the end of their lifespan and will require significant upgrades in the coming years. The good news is that each upgrade to a Pennsylvania bridge is also an opportunity to mitigate the negative impacts on wildlife and include habitat connectivity in design.

The Indian Creek Reservoir wetlands

Indian Creek runs through western Pennsylvania’s Fayette County, approximately 5 miles north of Frank Lloyd Wright’s iconic Fallingwater house and about 10 miles east of the borough of Connellsville. As it flows into the Indian Creek Reservoir (also known as the Mill Run Reservoir), it crosses under State Route 381 in Normalsville. Originally built in 1930, the bridge that allows State Route 381 to cross Indian Creek was scheduled to be replaced, with the work planned to
begin in 2012.

Pennsylvania Natural Heritage Program.Photo by Pennsylvania Natural Heritage Program | Public Domain

The S.R. 381 bridge and its approaching roads cross wetland habitat at the southern end of the reservoir. This area is partially included in the Upper Indian Creek Natural Heritage Area, which is designated as a Biological Diversity Area of state importance. The designation, made by the Pennsylvania Natural Heritage Program, indicates an area is home to species of special conservation concern at the state or federal levels, unique natural ecosystems, or exceptional native diversity. In addition to multiple rare plant species, the Upper Indian Creek Watershed is also home to numerous threatened animal species, some of whose precise identity and location aren’t disclosed to the public in order to protect them from illegal collecting[4].

Painted turtles have been observed in the reservoir, a species native to Pennsylvania that has been declining throughout its range. A major cause of painted turtle mortality is roadway deaths, specifically of females migrating to lay eggs. This leads to painted turtle populations located near roads to be disproportionately male and, consequently, to have fewer hatchings[5].

A wood turtlePhoto by Colin Osborn, USFWS | Public Domain

Another endemic species, the wood turtle, is a Species of Greatest Conservation Concern in Pennsylvania and being considered for listing under the federal Endangered Species Act[6] is also present in the wooded wetlands of the Indian Creek Watershed[7].

Culverts that help wildlife

The road bisecting this wetland and the surrounding floodplain had no crossings, and upon visiting the site PennDOT staff observed dozens of dead amphibians on the roadway approaching the bridge[8]. The reconstruction of the bridge and its approaching roadway provided an opportunity to incorporate culverts that would allow amphibians and reptiles to pass underneath.

Left: This pipe culvert is unfriendly to wildlife, misaligned with the water level and flowing at high velocity. Right: A “natural bottom” or “bottomless” culvert.Photo by Credit: Army Corps of Engineers | Public Domain

Traditional pipe culverts, which focus on allowing the flow of water, pose several challenges for aquatic wildlife. First, traditional culverts channelize the water and substantially increase how quickly it flows, which is inhospitable to most wildlife. At the same time, this rapid water flow can cause erosion, damaging habitat as the high-speed water travels through an ecosystem. Additionally, the bottom of the pipe is often misaligned with the ground or water level on either side, preventing animals from entering and using it as a crossing. By contrast, “bottomless” or “natural bottom” culverts act as an extension of the surrounding environment, making them easier for wildlife to use.

At this specific site, the culvert shape chosen was an oval pipe with a natural bottom, a shape demonstrated to be specifically inviting to reptiles and amphibians[9]. The project reached completion when the S.R. 381 bridge over the wetland was finished in 2014, and included several such culverts that facilitated the safe passage for many species of amphibians and turtles living in the wetland.

Additionally, these crossings were paired with new exclusionary fencing along the roadside to prevent animals from entering the roadway, instead redirecting them to the culvert. Return visits to the site by Pennsylvania Fish and Boat commission staff found no roadkill, indicating the tunnels have been effective at protecting wetlands’ wildlife as they move through the area[10].

A culvert entrance and exclusionary fencing as seen from S.R. 381.Photo by Stephen Wiedemer | Public Domain

References

1. Pennsylvania Department of Environmental Protection, Advice on Flood Prevention and Management on Streams, accessed: 5 February 2025.

2. Pennsylvania Governor’s Press Office, Shapiro Administration Gets Stuff Done: Pennsylvania Repaired More Poor-Condition Bridges Than Any Other State Last Year (press release), 3 October 2024.

3. PennDOT, Bridge Conditions, accessed at: https://gis
.penndot.pa.gov/paprojects/bridge-conditions, 5 February 2025.

4. Pennsylvania Natural Heritage Program, Upper Indian
Creek NHA (fact sheet), 13 January 2021, accessed: http://www.naturalheritage.state.pa.us/inventories.aspx, 5 February 2025.

5. David A. Steen and James P. Gibbs Effects of Roads
on the Structure of Freshwater Turtle Populations, Conservation Biology 18(4): 1143-1148. http://dx.doi.org/10.1111/j.1523-1739.2004.00240.x August 2004.

6. Pennsylvania Fish & Boat Commission, Wood Turtle
Conservation (fact sheet). Accessed at: https://www.pa.gov/agencies/fishandboat/conservation/reptiles-and-amphibians/turtles/wood-turtle-conservation.html 5 February 2025.

7. Mountain Watershed Association, Indian Creek River
Conservation Plan: The Sequel 2021, 2021.

8. Stephen Wiedemer, former Environmental Manager, PennDOT, personal communication, 28 January 2025.

9.  Ibid.

10. Ibid.

11. Pennsylvania Governor’s Press Office, Shapiro Administration Gets Stuff Done: Pennsylvania Repaired More Poor-Condition Bridges Than Any Other State Last Year (press release), 3 October 2024.