INTRODUCTION

Millstream Cleanup

 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. 

  Figure 1: 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: 

• creating pools and riffles for fish to rest in,
• slowing down the water current,
• creating turbulence in the water to increase oxygen renewal, and
• increase wetted area upstream

A.     Training and Planning

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 worksite

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 layer

Next, a second layer of large boulders was put into place, securing the filter fabric.

Figure 6: 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!!!