Constructing a riffle

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"The Telstra riffle" was our first major river construction. Built to solve a specific problem, this riffle in fact solved some other issues as well. The situation was that a major Telstra cable, originally submerged under the Dasher River, was hanging several feet in the air due to prolonged erosion of the river banks and bed. This left the cable very vulnerable to damage from debris carried by floodwaters.

After discussing the problem with DPIW's river engineers, our co-ordinators suggested to Telstra that a solidly constructed riffle would both protect their cable and prevent further erosion at the site. Telstra agreed, and also supplied funding for the construction. DPIW provided plans, and construction began.

This is a section of the Dasher river before the construction of the riffle.



















This is where we learned that a substantial riffle requires a lot of rock - more than the engineers had estimated (roughly twice as much). The picture below shows rock being delivered to site.

Large boulders were strategically placed to form the basis of the riffle across the whole width of the riverbed. Some of the boulders were very big indeed!


















Below is the completed riffle, viewed from upstream during summer at low water levels. The calm area above the riffle is a deep pool and a favourite spot for fish and the riffle contains passages allowing fish to move freely up and down the rivers.