Providing Low Water River Habitat for Trout !

Bow River Boulder Garden Project 1996

    In 1996, BVHD completed a boulder habitat enhancement project on the Bow River, in the Town of Cochrane, Alberta. Due to extreme water level fluctuations caused by a hydro dam upstream, during non-peak demand for electric power, the river levels are very low. This creates a stressful daily experience for sport fish that reside in the river. The fish are required to move from a high flow habitat too a low flow habitat within a 24 hour timeline.

    To reduce the stress for some of these sport fish, low water boulder habitat was created at key locations on 5 different sites over a 3 kilometre reach of the Bow River. In total, 133 class 4 and class 5 rocks were placed in double and triple rock placements at the sites. The large rocks were seated into the riverbed with the top of the boulders at or slightly above or below water level, during low flow periods.

    The objective was to create refuge for shoreline trout and mountain whitefish when the river levels were dropping, after the main turbines at the power plant were shut down. The sport fish would not have to move as far up or down the river channel to find acceptable cover habitat when the levels are receding. This completed project would enhance both sport fish populations in the specified boulder site areas and it would also reduce the stress levels for trout and mountain whitefish.

Left Photo:

    You can see that the class 4 and class 5 quarry rock used in this project was very large, in comparison to the 355 Hitashi Track Hoe and Cat 980 loader that were used in this program.

    The spoil from seating the rock into the riverbed was used to create low profile berms along the shoreline of the river. These berms would also create a current break and eddy, when the river levels are at normal height.

Above Photo:

    This photo was taken from the Highway 22 Bridge over the Bow River. You can see the series of double rock placements installed on the riverbed in this deeper run. The double rock placement design is best suited for deeper areas such as this.

Right Photo:

    This is a 2004 photo of a triple rock placement under low water conditions. A small pocket pool was excavated in 1996, when the project was carried out on the river. You can see that it has maintained its position and the pool is still evident.

Left Photo:

    This is a double rock placement in a shallow riffle area. Note the scour around the large rocks. It is in this area around the boulders that sport fish utilize, during low flow conditions on the river. No pool was excavated below these boulders in 1996.

Above Photo:

    The triple rock placement is the most effective boulder design for a small cluster of rocks. The single apex rock is always positioned in the center, upstream of the two lower wing rocks.

Assessment of the Sites has Proven Very Positive Results!

    The boulder sites have been assessed twice by electro fishing and once using underwater video equipment. The two electro fish programs were conducted during high flow events, but the results proved to be very positive. However, because the habitats were created for low flow conditions, it was necessary to conduct a video survey of the sites at low water conditions. This was completed in 1998 and 1999. The video footage at the site selected for assessment, showed hundreds of both mountain whitefish and rainbow trout utilizing the boulder habitats. The double rock placement shown in the photo above, left, had approximately 9 trout holding around it in the 1998 video and 14 trout and 6 whitefish holding around it in 1999! I have fished these sites over the years with good success, since the project was completed!

Above Photo:

    This is a Bow River rainbow trout that was caught at one of the boulder sites in 2003. They are pretty unmarked trout that do not grow as large as the rainbow trout that have made the lower Bow River famous!

Bow River Boulder Project

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