The natural process for smaller sediments is for the river to move them downstream during spring runoff events. As gravels get swept downstream, they are replaced by new gravels from upstream. Dams, such as Lucky Peak, interrupt this process and prevent new upstream gravels from entering the river. Over time this leads to a loss of the smaller gravels that trout need to spawn.

To improve trout spawning habitat, both Trout Unlimited and Boise Valley Fly Fishers have done gravel augmentations on the Boise River. BVFF’s two gravel augmentations in 2021 and 2023 were done in a side channel between Glenwood bridge and the head of Eagle Island. Over the last several years we have monitored the side channel and can tell that the gravel has moved from its original location, but it is impossible to know where it went. We have observed new gravel accumulations in the lower end of the side channel that we think are from our augmentation, but there is no way to know for sure.

Here are some Conservation Blog entries with information about those augmentations, plus observations of the gravel migration.

BVFF 2020 Augmentation

Side Channel Gravel Refresh 2023

TU Gravel Augmentations

Where Did The Gravel Go?

BOISE RIVER HIGH WATER AND TROUT HABITAT

We have been working on a gravel augmentation for the Owyhee River in Oregon to improve the trout spawning habitat in the lower section of the river which has much less spawning activity than the upper reaches. This project started back in 2022 and it has taken several years to obtain the necessary permitting. We have our permits and the augmentation is planned for this October. Here’s are a couple of conservation blog entries that talk about the initial Owyhee River Brown Trout Redd Location Study and our plans to do the augmentation.

Brown Trout Redd Location Study

Owyhee Augmentation Details

We have confidence that brown trout will adopt the gravel we add to the river, although it may take a few years before they utilize the entire augmentation area. But a big question everyone has is how long the gravel will stay in this location. Our observations on the Boise River is that the gravel we added stayed in place as long as flows stayed below 2,000cfs, and we expect a similar experience on the Owyhee. The Owyhee is a lower gradient river than the Boise and experiences fewer high water events. Here is a historical graph of Owyhee flows. You can see that flows only exceeded 2,000cfs 6 times in the last 25 years, with two of those being the last 2 years. Based on that, it’s likely that we won’t see another high water event for several years, so we are hopeful that will give the brown trout plenty of time to start using the gravel.

BVFF and ODFW are interested in determining how long our gravel stays in place. If it stays around long enough and is helping recover the brown trout population in the lower river, then we would try doing a second gravel augmentation. We have looked into different ways to track gravel migration and are investigating using radio PIT tags. We have met with local company Biomark, who is a leader in PIT tagging and tracking and is interested in partnering with us on studying gravel migration.

Club member Jeff Jones, a retired geologist, has been leading the project investigation. A few days ago, Jeff and I experimented with samples of ¾” gravel and were able to add a PIT tag as well as detect that tagged piece of gravel in a bucket full of gravel—a promising proof of concept! We are planning to tag 1,000 rocks and are looking for volunteers who are interested in helping cut the rock, add PIT tags and seal them with epoxy. Please reach out to us at conservation@bvff.com if you are interested in helping with this rock tagging project. We could use more small offset grinders to speed up the process of cutting the rock.