Thank you to the committee for this opportunity to speak to you today.

At the outset, I want to note that I did speak to this committee a couple of years ago, as some of you may remember, on the topic of the impact of commercial shipping on shoreline erosion. At that time, I summarized a study on the St. Lawrence River that I was conducting. I reviewed the physics of large-ship wake waves in narrow channels, new measurement technologies, nature-based shoreline protection strategies and current research needs. Here, in collaboration with my colleague Professor Jesse Vermaire from Carleton, I'll discuss wakes produced by pleasure craft.

The likelihood of a boat wake contributing to bank erosion depends on the power of the waves; the water surface elevation with respect to the bank; and bank characteristics that determine bank stability, such as bank angle, sediment grain size, cohesion, consolidation, pore pressure and vegetation. It's not only large ships that may induce shoreline erosion; smaller pleasure craft can also generate relatively large waves. Wake boats, as an example, are specifically designed with a deep draft to induce a large wake for recreational purposes, such as water-skiing.

While pleasure craft are generally too small to generate a large primary drawdown wave, which is what I discussed on the St. Lawrence, the subsequent V-shaped Kelvin wake wave can be large enough to erode shoreline bank sediments. This has been documented in some previous studies. For example, as reference, Bauer et al., 2002, estimated erosion rates of between 0.01 millimetres and 0.22 millimetres per boat passage. That's a small amount per passage, but the cumulative effects of thousands of passages could be substantial.

We believe there is a need to identify where zero-wake zones and speed limits are required to reduce shoreline erosion and ecological impacts associated with recreational watercraft use.

Pleasure craft boat wake has been implicated as a possible contributor to shoreline erosion on the Rideau Canal waterway. As part of a larger NSERC-funded study in collaboration with Parks Canada, we've been working on measuring boat wake waves and turbidity associated with various pleasure craft in the Rideau River. We have a study site near Eccolands Park, just south of Ottawa.

The experimental design involves running various individual boats at set speeds and distances back and forth past an eroding river shoreline cutbank. I will focus here on three boat types—an 18-foot bass boat, a 22-foot wake boat and a 29-foot small cruiser, as you would typically see on the Rideau. The boat speeds we used were slow, medium and fast for each type of boat. The distances from shore were 30 metres, 60 metres and 100 metres.

We collected various data with several instruments, but here I'll focus on water level and turbidity collected with an RBRduo instrument at 2 hertz. We placed this instrument six metres from shore to measure the waves and the turbidity. I also took repeat measurements of the bank over a couple of years using a survey-grade GPS to monitor recession of the bank.

As each boat passed and the wake wave train impacted the riverbank, sediments were entrained, resulting in increased turbidity. We processed the water level data to extract what's called the “significant wave height”, which is the average of the top one-third of the waves in the wake train. We also processed the turbidity to see how much the increment in turbidity was during that passage of the boat.

We have a number of preliminary observations.

First, wake waves from pleasure craft dissipate as they propagate. Thus, waves impacting the riverbank are larger if generated near the shore than if generated farther from shore. This is even on a small waterway like the Rideau. We could see a difference based on how far away the boat was.

Each boat produced a maximum significant wave height when run at medium speed. This is because at medium speed, the boat is not planing, and thus pushes more water and displaces more water. For the three boats that I'm talking about here, the medium speed was on the order of 20 kilometres per hour.

Maximum significant wave heights produced by the small cruiser and the wake boat were similar, on the order of 15 centimetres. This was larger than those produced by the bass boat, which was on the order five centimetres.

The turbidity increment increased almost linearly with the significant wave height, which suggests that shoreline erosion will be a function of wave height.

Lastly, I did measure a recession of the bank over a year's time. It was 10 centimetres at the bank top and about half a metre at the bank bottom, suggesting that the bank is getting steeper over time.

Thank you.