The Constructed Log Pool Habitat

It has always been my ambition to create an in-stream and riparian fish habitat that blends into the environment. This has been the case in all of my projects, over the years. The constructed log pool habitat is one of my best contributions to the field.

The pool habitat shown above was constructed a few years earlier, on a no-name creek near the community of Hinton, Alberta. Bow Valley Habitat Development was involved in project design and implementation. The BVHD Log V-weir design was used for creating a self-cleaning pool habitat on a small stream.

The structure is used for compensation work for pipeline and electric power transmission right of ways. The design is also included in stream restoration projects.

A Few Years Earlier

In 2006, a visit to the site was made, to complete some survey work. Also, some consultation and discussion of ideas of where some pool habitats would fit in nicely were carefully considered during that visit. The project site for one of the log pool habitats was photographed and it is shown below. I will use this particular project for this construction overview.

The pool site below is what the stream channel looked like in the year 2006. The log v-weir would be installed right where you can see the flow going over a log in the streambed. As you can see, the streambed is close to the surface at this particular spot. It is located at the bottom of a long narrow riffle, in the creek, upstream. All of the surrounding vegetation would be protected during the construction phase.

The stream that I was working on had a population of small brook trout, so pool habitats are always a winner for brook trout habitat. The brook trout is very gregarious and numerous trout can be found in one good pool habitat.

The first thing to do, when you are going to construct a pool in-stream, is to deal with proper silt containment measures. I use a flow by-pass that I constructed and also some permeable silt fabric for my silt fences. The excavation work is done while a flow by-pass is diverting clean water around the channel where you are working. Proper silt fences are used on the downstream end. On most projects, I like to use two silt fences downstream.

Detailed instructions of how silt containment will be carried out, is required in the permitting process, so you need to have a thorough plan of what you are going to do.

Prior to blocking off the escape from our work area, all fish, including trout are netted out of the confined area. I will go into more details further on in this overview. There was an environmental inspector on-site, during most of the early part of the project.

The log v-weir is a very effective design for use in constructed pool habitats. It concentrates the flow into a narrow thalweg that creates a scouring force that keeps a pool deep and clean of silt, directly below the weir. With frost heaving being a major problem on all northern streams, the structure needs to be well anchored, so it is.

Log V-weir construction

The photo below shows how I make up my log v-weirs. First, the logs are joined at a 45-degree cut. I custom made some angle iron brackets to hold the logs together, while the holes for the rebar pins are drilled and also the 12-inch spiral spikes are driven in using a heavy framing hammer. The 3/4 inch rebar can also be used as an attachment point, for a cable anchor, when installing the weir.

Before the entire log v-weir is placed into the streambed, a galvanized apron and a silt fabric liner are added to the upstream side of the v-weir. I use galvanized roofing nails for prolonged life under the water. The galvanized mesh apron is used as an additional anchorage. The silt fabric liner is permeable so it lets water percolate thru, at a slow rate. Eventually, the material upstream of the log v-weir will pave or harden like concrete.

Five gallon buckets are a great tool for hauling material to site and also storing soil until the project is at a stage where some of the soil can be put back in place. Lots of rock is used in the construction of this log v-weir design, so having it on hand for installation saves a lot of time.

The log structure needs to be leveled and positioned at the right depth in the streambed. The apex of the v shape has to be considerably lower than the wings of the structure. During installation, large rocks can be added to help stabilize the weir at the right height and angle.

The rebar pins in the log v-weir are driven into the streambed, for added stability. There is a cable attached to the apex of the log structure and this is attached to a steel anchor pin that is driven into the streambed, upstream of the weir.

The rock used at the end of each wing will prevent erosion from scouring around the structure. The design is made to withstand annual frost heaving. It can move up and down at the contact points with the stream bank, during the spring thaw and winter freeze up.

The site is now ready for final landscaping and the pool deepening part of the project. First, the stream banks need some attention.

Maintaining a narrow stream channel at the log v-weir will help to keep the flow of the stream directed into the apex.

This is the log v-weir 4 years after the project completion. The far stream bank at the site was preserved, with its natural undercut bank and shady cover. The pool is over a metre in-depth and I could see small brook trout living in the depths.

Removing Fish From A Project Site

I have used electrofishing and trapping to remove trout from certain areas of streams, but the most effective method is netting. You can cover the entire area of a pool, using a fine mesh net, with a steel cable weight on the bottom. I like to work around the outer edges of an area and then heard the fish into a closing circle of the net. It works great if electrofishing doesn’t do the job.

Another Example of a pool habitat

Below is another example of a pool habitat, from before until a few years later.

This deep pool habitat looked pretty rough during construction, but if you see the photo below, you can appreciate the final product.

The pool now has some willows growing around the edge and trout hold in the deep water. Here is another look at it below. The photo was taken a few years after the project was completed.

Can you see the trout in the photo below? If you look carefully, you will see two trout. If you look long and hard, you will find three small trout in the photo. Zoom in, if you like.

The Log V-weir design

The original design didn’t have the galvanized wire mesh anchor apron. I have some sketches of a design for a larger stream that I will share with you. This sequence of drawings will give you an idea of how the v-weir is placed in the streambed, but you should consider that fewer anchor posts are used on smaller streams. However, the basic design is the same.

The top view shows what the structure looks like with most of the components included.