In September 2000, the Veins of Life Watershed Society
undertook the task of constructing two Newbury rock weirs in the
Millstream Creek along Selwyn Road. The Millstream creek
runs through the District of Langford in the Greater Victoria
Region. The locations of the weirs were chosen by a hydrologist
from R. Irwin Consulting Ltd. during a Fisheries Habitat Assessment
and Enhancement survey performed in April 2000.
Location of the work site along the Millstream Creek in Landford
A weir is a formation of strategically placed rocks in a stream.
It improves the fish habitat by:
Currently, the Millstream supports a population of cutthroat trout.
The purpose of this project was to increase the fish population.
The following is a technical diagram of the Newbury Rock weir.
- creating pools and riffles for fish to rest in,
- slowing down the water current,
- creating turbulence in the water to increase oxygen renewal,
- increase wetted area upstream
A. Training and
Team supervisors introduced the work crew to the fundamentals
of weir construction, the proposed site and the necessary safety
precautions to be taken (ie personal protective equipment required).
B. Equipment Used
Shovels, rakes, filter fabric, wheelbarrows, a crowbar, handsaws,
boulders and rocks (of various sizes and shapes), a gas powered
water pump, hoses, sandbags, PPE (personal protective equipment),
plastic to cover sandbags, and hay bales.
C. Construction of the Weir
1. Site Preparation: Before work on the weir could
begin it was necessary to prepare the work area in order to minimize
our impact on the environment. Our main concern was that
silt from the streambed, disturbed by our work, would spread downstream
reducing the clarity of the water. Also, the water level
in the work area had to be lowered in order to excavate the streambed
and place the base rocks.
Figure 2: Diverting the creek around the
First, sandbags were placed on either side of the proposed weir
site approximately 10 feet away. Three hoses were placed
between the layers of sandbags to carry the streamís water flow
through the worksite. The final height of the sandbags was
sufficient to dam the stream. A plastic sheet was tucked
around the sandbags to further impede the flow of water.
A silt barrier was constructed downstream of the first site to
catch sediment using filter fabric and logs found in the stream.
At the second site, hay bales were used in conjunction with sandbags
to catch the sediment. Once the site was dammed, a gas powered
pump was used to lower the water level in the weir site.
Figure 3: Sand bags and Hay Bales used
to Stop siltation downstream
2. Excavation of Streambed and Anchor Sites: Once
the water level was sufficiently low, the streambed was excavated
3 inches using shovels. Also, anchor sites were excavated
on either side of the stream.
3. Rock Placement: Large boulders of various
sizes were placed in the excavated areas to form the base layer.
All of the rocks used in the construction of the weir were rolled
down the stream bank. When the base was completed, a layer
of filter fabric was placed over the boulders.
Figure 4: Filter fabric laid over first
layer of boulders
will trap sediment to further enhance effectiveness
of the Weir
Figure 5: A second layer of large boulders
to hold the filter
fabric in place and to give shape to the final
Next, a second layer of large boulders was put into place, securing
the filter fabric.
The upstream, or approach, beginning to take shape, showing
the concave form and 1:5 ratio slope
The weir was extended lengthwise until it attained a ratio of
length to height that was approximately 5:1. To create a
smooth water flow over the weir, flat finishing rocks were placed
on top creating a convex shape. It is not essential for
spaces between the rocks to be filled as these spaces permit passages
through the weir and promote habitat diversification.
Finally, small rocks were placed along the banks extending beyond
the weirs to prevent erosion and scouring of the banks.
D. THE FINISHED WEIR
Figure 7: The finished Weir at the first
site, looking downstream
4. Clean Up: The stream diversion and sandbags
were removed. A silt fence was built on the bank in the
area in which we had been working in to prevent sediment from
washing into the stream in the event of a rainfall. Woody
debris was dispersed to naturalize the work area, and finally,
native species such as Maple, Pacific Ninebark, Douglas Fir, Grand
Fir, Alder, and Western Red Cedar were planted to encourage diversity
of species, provide habitat, and prevent erosion.
Figure 8: A silt fence at the bank side
keeps silt out of the creek
until replanting of native species can take place
Lifting Rocks Can Be Tiring!!!