Motor Boat Science
The motor boat sector disputes that erosion is caused by boats despite considerable scientific documentation to the contrary, including local research in 2013.
"[...] there are now sufficient numbers of studies that have provided convincing evidence for the negative cumulative impact of sustained boat traffic on river banks [...] The study seems to indicate that boat wakes do indeed contribute to the erosion problem on the Lower Shuswap River [...]" (Laderoute & Bauer 2013).
In 2014, Cameron and Bauer conducted an additional study that showed the problem was even greater than originally described.
"The implication is that boat-generated waves may be of relatively greater importance (than the spring freshet) in forcing bank change throughout the annual cycle than had previously been anticipated." (Cameron & Bauer 2014).
Also of concern is the pollution from motors designed to operate on water.
"A certain amount of the fuel that enters into a motor is discharged unburned, and ends up in the water [...] Estimates vary as to how much fuel may pass into the water column, 25-30% is a reasonable average, and depends upon factors such as engine speed, tuning, oil mix, and horsepower." (T. Asplund 2000)
Asplund goes on to document the chemical pollutants discharged into the water, including polyaromatic hydrocarbons, some of which are known carcinogens, and methyl tert-butyl ether, a suspected carcinogen. (T. Asplund, 2000).
"Adding to this, it is generally accepted that increased recreational boating along the Lower Shuswap may be further exacerbating erosion of these un-vegetated and destabilized banks." (Hawes, Schleppe & Jantz, 2011, pg iv).
"Based on the inventory results, there is a lack of deep water holding pools/thermal refuge areas downstream of Enderby to Mara Lake. This, in conjunction with more intensive landuse and recreational pursuits (namely boating), presents concerns for Fisheries staff relating to the potential stress on migrating adult salmon." (Hawes, Schleppe & Jantz, 2011, pg 68).
"Watercraft can impact the biophysical values of waterbodies through fuel and exhaust emissions, noise pollution, direct contact with flora and fauna, and hydrodynamic impacts such as wake-induced shoreline erosion and turbulent prop wash. In terms of the hydrodynamic impacts, recent studies have correlated boat waves to an increase in shoreline erosion and stirring of bottom Sediments (Hill et al. 2002). In other studies it was concluded that the wakes contributed a significant amount of bank erosion and sediment disturbance near the bank was markedly increased for wake heights exceeding 13-14 cm." (Hawes, Schleppe & Jantz, 2011, pg 69).
"With 81% of the docks recorded on the Lower Shuswap River occurring in Reaches 1 – 5 (Mara Lake to Enderby), it is plausible that more intensive watercraft use and operation is a factor in decreased bank stability and increased erosion. The hydraulic character of the lower reaches is a low gradient, low velocity, straight to sinuous glide, with generally low erosive forces. However when combined, the lack of riparian vegetation and boat wakes may be a key causal factor of observed erosion along the river bank in lower reaches." (Hawes, Schleppe & Jantz, 2011, pg 69)
TRUE OR FALSE? SOME FACTS MANY PEOPLE GET WRONG
- Boat wake can’t cause any more damage than wind-driven waves. YES IT CAN.
Wind driven waves tend to travel along the length of the waterway and directly approach the shore only at bends in the channel. But boat wakes may travel almost directly towards the bank and can cause erosion along the entire length of the waterway.
Most ‘tinnies’ are small and light enough not to cause any wake problems. NO THEY'RE NOT.
Speed is just as important as size, and both factors must be considered together. For their size, most outboard powered boats can travel much faster than almost anything else on the water.
On the plane, the smaller wake causes less damage. NO IT DOESN'T.
Even though a wake reduces in height as the boat planes, the waves are moving faster, further and travelling outwards from the vessel track. When a planing vessel travels parallel to a sheltered shore, the wave energy is directed towards that shore.
You can see what your wake’s doing from the boat. NO YOU CAN’T.
Even if you’re fairly close to the bank (say 50 metres away) the peak wake impact of a boat travelling at 20 knots only occurs as the first 5–10 waves hit. By that time, you’re half a minute and 300 metres away. The only way to really observe the impact of wake is to stand on a soft shore and watch the impact of wake in all three phases of boat speed. Every boat driver should do this sometime – you may be surprised at what you see." (Tasmania Dep't. of Primary Industries)
— REFERENCES —
Abbott, J.C. and G.O. Stewart, Envirocon Pacific Ltd. "Sockeye Salmon In-gravel Survival Rates for Clemens Cr., Adams, Lower Shuswap, Birkenhead, Seymour and Horsefly Rivers during 1986-87". (Figure 3 and A.10) Prepared for Fisheries and Oceans Canada, May 1987.
PSMFC - Pacific States Marine Fisheries Commission. "3.0 Description of Adverse Effects on Pacific Salmon…" psmfc.org. January 1999. Extracted Nov. 11, 2015 <www.psmfc.org/efh/Jan99-sec3-1.html>.
Tasmania Dep't. of Primary Industries, Water and Environment. "Wake up? Slow Down!" ISBN 0724663665. Undated joint publication with Tasmania Marine and Safety, Inland Fisheries Service, Australian Maritime College and Hydro Tasmania.