|The finished riffle with the water babbling over the stones
|This is a concept drawing of the constructed riffle structure built in Bilston Creek at Lippincott bridge. Cobbles selected for this project were hand picked to be rounded glacial till as would be found in a natural stream bed condition.For a number of years, elevated iron bacteria levels have been observed to originate in this area. This causes an orange, spongy deposit on the stream bed and plants. Though not directly harmful to fish, this interferes with and reduces the growth of feed organisms, and well as being unsightly. A series of two riffles in Bilston creek are designed to raise the level of holding water upstream by a few inches which will, hopefully, restrict the amount of iron rich groundwater from seeping into the stream. As well the water flowing over the riffle structure will increase the amount of oxygen in the water. In the Firehall creek tributary, three riffles were constructed which are intended to increase the oxygen as well. Though this section of Firehall creek dries up in the summer, it is seen as possible spawning area during the spring, after which the fish would migrate downstream. An increase in oxygen will also assist in the breakdown of the spongy deposits, thus increasing food production.
|This shows the temporary sand bag and plastic sheeting dam built to prevent water, debris and fish from entering the area worked on. Water flow here was so low at the time, no bypass flow pipe or channel was needed. Water level upstream simply increased a few inches during the day. The streambed was excavated about 30 cm to reach a stable base.
|Here the stones are in place. Some final sorting and placing of the larger stones on to the top of the structure was done by hand.
|An excavator was used to scoop out and profile the stream bed. This method reduces greatly the damage done to adjoining areas by many trampling feet if this was done by hand. Release of silt into the stream was almost nil as the machine was placed back from the bank on the road. Evidently there is still hand work, the machine doesn't pick everything up off the road without some help.