Culverts and the fish who love them

By Kevin Davis, USFS
Reader Contributor

Do you enjoy fishing in North Idaho? Or, perhaps you like to fish for kokanee on Lake Pend Oreille? Are you fly fisherman that enjoys the seclusion of fishing in mountain streams?  What about hiking up to a high mountain lake and bringing your light-weight spinning rod on the off chance you might catch a native cutthroat trout?

A variety of fish populations are distributed widely across North Idaho and you can catch fish just about anywhere you go. The fisheries division with the Idaho Panhandle National Forest is working to make sure that fish are well distributed across their range and have the ability to increase their population. One way to do this is to make sure that fish can access their range of available habitat.

The old 5-foot diameter Quartz Creek culvert taken circa 2010. Photo by Kevin Davis.

Many miles of forest roads wind across the landscape. At every stream crossing you’ll find a culvert that passes the stream under the road. Some of these culverts pass the water but not the fish. If culverts are too small, have a big vertical drop at the outlet, or are too long, fish are not able to navigate to their upstream habitat.

These blockages present a variety of problems. Culverts may prevent fish from accessing suitable spawning areas. In the summer when water temperatures are rising, fish that reside in mountain streams tend to migrate upstream where water temperatures are cooler. If fish populations are healthy, undersized culverts can prevent fish from expanding their range.

For the past several years the Sandpoint, Bonners Ferry, and Priest Lake ranger districts have been identifying those culverts that are fish migration barriers and replacing them with larger culverts—and in some cases, bridges.

First, the streams are surveyed to identify the quality of stream habitat. Then the type of fish and their approximate distribution in the stream are identified. The Forest Service focuses on native fish species such as cutthroat trout and bull trout, but also prioritizes important game fish such as kokanee and Kamloops.

If the crossing is considered a problem and it would benefit fish to replace it then the culvert is surveyed and a contract is made to remove the existing culvert and replace it with a larger structure. These contracts are called Aquatic Organism Passage projects (AOP). In addition to fish and aquatic insects, AOPs also benefit more terrestrial creatures like frogs, salamanders and turtles.

In the case of the North Fork of Grouse Creek, an old culvert that blocked fish passage to miles of good habitat was replaced with a bridge. All age classes of fish now swim freely through the crossing benefitting cutthroat, bull trout, and Kamloops trout.

The new 25-foot width by 13-foot tall Quartz Creek Arch culvert taken in 2014. Photo by Kevin Davis.

The Quartz Creek culvert on the #419 road in Upper Lightning Creek was replaced three years ago. In addition to fish passage problems this culvert had a high risk of plugging and washing out the road. The five-foot diameter culvert was replaced with a 25-foot bottomless arch pipe designed to pass flood waters and log debris.

The stream channel under the pipe was also constructed to match the natural channel. This technique is called stream simulation and is good insurance that the constructed channel will be stable and not create fish passage barriers.

More culverts that present barriers to fish are being replaced this summer. Shertz Creek, a tributary to Trout Creek near the mouth of the Pack River and Quartz Creek a tributary to the Priest River are under construction in September.

Many rusty culverts are in need of replacement anyhow since they were first installed more than thirty years ago. It makes sense to take the opportunity and improve our fisheries as well as our road infrastructure.

When you’re out driving a forest road this summer and cross a stream, take a look at the culvert. Is there a lot of gravel deposited at the inlet? Is there a vertical drop at the outlet? Are there fish in the creek?  If you answer yes to any of these questions stop in your local Ranger District office and let us know. It may be on our list to fix or it might be one we didn’t know about.

We’ll work to ensure that our fisheries in North Idaho have the best chance to flourish well into the future for many generations to come.