Rocky Road (culvert woes, not the ice cream)
We shouldn’t put a road across a river until we know it. Really well. Does it have some baggage? Like that time it flooded back in 1978? Planning around the entirety of its behaviors can help us avoid a rocky road of costly maintenance, safety concerns, and fish passage problems.
Plan for the 1 Percent
September 2012 — a week-long storm triggered severe flooding, overwhelming roads in Alaska’s Matanuska-Susitna Borough. Willow Creek rose three feet and swelled to roughly ten times the volume it carried the previous week. Montana Creek ate away at and commandeered Yoder Road. Oil Well Road, West Kenny Boulevard, and others washed out. People were stranded. The Governor declared a federal disaster and FEMA stepped in.
Each year, there’s a 1 percent chance that a flood this big (the so-called “100-year” flood) will occur. It’s a mistake to think it’ll only happen once every century. Though statistically unlikely, it can happen many years in a row. In fact, Alaska has seen multiple 100+ year floods in the past 20 years. Floods that have caused road failures on the Kenai Peninsula, Kodiak Island, and across Mat-Su. A major culprit? Culverts that aren’t designed to give rivers and streams room to be their natural, dynamic selves:
Rusty Reminders
It’s a common sight: the culvert graveyard. Where mangled 12 inch diameter pipes, 18 inchers, and 4-footers languish and rust, cast aside after each blowout to make room for the next size up. Culvert remains are also in our roads, filled with debris, unearthed only when excavators come in to make way for new pipes.
These graveyards serve as reminders that rivers and streams are powerful and ever-changing. They carry fallen trees, boulders, and heavy loads of silt. They flood. They carve up the landscape. And when they encounter culverts not custom-fit to carry them through roads and railways they find ways around:
As water volume increases during heavy rain, it can’t physically drain through a too-small culvert fast enough. Things worsen when it clogs with debris. Water backs up, forming a reservoir and putting pressure on the road. Roads aren’t designed to be dams and can be over-topped or washed away under the strain.
Let’s consider the other end of the spectrum. Where intersections of transportation and river networks are designed to retain the character of the natural channel and reduce risk to the road. This can be done using a technique first developed by the U.S. Forest Service called stream simulation:
Pay Now or Pay Later
Despite more cost upfront, stream simulation has a growing track record of increasing infrastructure longevity and lowering (sometimes even eliminating) costly maintenance. What’s more, return on investment may become even more pronounced in the future. A recent study predicts climate change-related expenses to Alaska’s public infrastructure increasing through the end of this century. The largest total predicted damages involve roads, with 75 percent of damage caused by flooding. Planning and building better road drainage systems could reduce predicted flood damages by an order of magnitude and significantly reduce the cost to maintain Alaska’s roads.
Given expense and long-term liability, it’s also worth considering if crossing streams can be avoided completely. And if not, where along the stream’s length is best to cross. Like higher upstream where there’s less floodplain and volume of flowing water.
Before 2012, the Mat-Su Borough had already been working with partners to install stream simulation culverts for another reason: salmon. At 81 road-stream intersections to be exact (as of 2017, the number has grown to 108). They held fast during the 2012 flood.
Vermont had a similar outcome in 2011. Tropical Storm Irene damaged or destroyed nearly 1,000 traditional culverts. Stream simulation culverts in Green Mountain National Forest fared much better. They’d been designed for Brook Trout passage and better performance during storms.
It turns out designing culverts with this in mind is good for the bottom line. The Mat-Su and Kenai Peninsula boroughs and Municipality of Anchorage recognize this. They’ve adopted proactive, preventative ordinances that include fish-friendly standards and designing new crossings to accommodate at least the 100-year flood.
Jim Jenson, the Mat-Su Borough’s operations and maintenance manager, is responsible for maintenance of roads and vehicles. He’s seen the benefits of stream sim culverts firsthand:
“The 2012 flood cost millions of dollars in road damages where we still had low capacity culverts. Now when we put crossings in we make them bigger and put rocks in them for the fish. A big benefit is they pass the floods.”
The Native Village of Tyonek is another Alaska community that’s had enough with their roads blowing out and disrupting people and fish. Like Mat-Su and the western Kenai Peninsula, Tyonek has a lot of intersecting roads and salmon streams. A number cross “flashy” streams that rise and fall quickly with storms. They have a history of frequent blowouts and more than thirty don’t pass juvenile fish. Tyonek’s only accessible by air or barge, so infrastructure and repair costs are even higher. Making each decision more important.
Christy Cincotta, Executive Director of the Tyonek Tribal Conservation District, says:
“The reason we really like these projects is they’re a win-win. Developers need to be able to get places on the roads out there and if they’re washed out projects can get delayed. In 2012 and 2013 the only roads that didn’t wash out had been replaced with fish-friendly culverts. Everyone’s on board.”
Design
The foundation of a well-designed road-stream crossing is good information. More extensive on-the-ground assessments of a stream come at a nominal cost.
Compared to other states, Alaska is lacking long-term flow data. Specifically, the data from instruments (“gages”) placed on rivers that measure the volume of flow through time. Gage data that captures extreme flows is, as you’d guess, very useful. Without it, hydrologists must rely on equations that use weather statistics and land cover to predict flows. These estimates can have wide margins of error.
Construction
The highest cost tends to be the larger culvert itself. Other costs include deeper excavation and labor/equipment to move the streambed and streambank materials to site and into the crossing. In Alaska, it typically costs 5 to 20 percent more to do it right the first time. However, long-term savings can far exceed those costs. It’s similar elsewhere: a study contrasting different culvert designs in Vermont found that stream simulation increased construction costs 9 to 22 percent, but the cost of repairing traditional culverts after Tropical Storm Irene exceeded that by over four times.
Maintenance and repairs
Mobilizing heavy equipment and materials for routine or emergency repairs is costly and can directly impact drivers. This is where stream simulation shines, offering long-term cost savings.
Costs to Alaska’s Fisheries
This externality isn't reflected in the price tag of old-school culverts. In Alaska, people’s livelihoods and ways of life depend on fish. So do Alaska’s multi-billion dollar commercial and sportfishing industries.
Between 2001 and 2017, Alaska Department of Fish and Game looked at 3,099 crossings on state and local roads. They estimate 40 percent are full or partial barriers to weak-swimmers like Arctic Grayling and baby salmon.
On Tongass National Forest roads, there’s a similar pattern: 34 percent of 2,019 stream crossings have documented fish passage concerns. According to Gillian O’Doherty, a habitat biologist with ADF&G:
“We’ve assessed over 90% of culverts in the state for fish passage impacts. We also look at their condition and age and help develop initial cost estimates for replacement. That data’s publicly available in ADF&G’s interactive online mapper.”
Fish passage at roads matters. For Alaska’s fish, being able to move at the right time can mean life or death. They move between feeding areas, ice-free overwintering areas, and cooler areas during summer. They must quickly find refuge during high and low flows and temperatures. Many (20 to be exact) are anadromous — they migrate (sometimes thousands of miles) between their freshwater birthplace and the ocean and back. Migration maximizes growth and reproductive potential, but quickly becomes disadvantageous when culverts cause delays or dead ends. Alaska can learn from the Lower 48 states, where roads rank second only to dams as the biggest obstacle to salmon recovery.
Decades-long research in western Alaska by the University of Washington has shown that stability of wild salmon fisheries depends on diverse freshwater habitat options. Similar to diverse investments and financial stability. In allowing passage under a range of flows, stream simulation helps fish keep their options open.
The New Norm
With roads and fish, Alaska can have its cake and eat it too: it can have durable roads where streams move seamlessly and fish swim freely underneath.
Learn More
The ADF&G Fish Passage Improvement Program and USFWS Fish Passage Program jointly offer free fish passage workshops. For more on Alaska’s fish and their habitats, follow us on facebook and subscribe to our newsletter!
This story is adapted from its original version in Alaska Business Monthly’s June 2018 Transportation issue. Katrina Liebich is the Alaska Fisheries Outreach Coordinator for the U.S. Fish & Wildlife Service.
In Alaska we are shared stewards of world renowned natural resources and our nation’s last true wild places. Our hope is that each generation has the opportunity to live with, live from, discover and enjoy the wildness of this awe-inspiring land and the people who love and depend on it.
