Discussion of Results

Wave Height:

The MasterCraft X-Star boat produced the largest wave height of the three boats studied.  This is not surprising since the X-Star is mainly used for wakeboarding, a sport that requires a large wake.  At low wind speeds, the wind wave height was less than the boat wave height for all boats.  As the speeds increased, however, the wind wave height eventually surpassed the boat wave heights, since boat wave heights decrease with speed and wind wave heights increase with speed.  The  wave height from boats could be greater than or less than those from the wind based on the boat type, the boat distance from shore, the boat speed, and the wind speed.

For wave height calculations and graphs, click here.

Wave Power:

The results show that the wave power produced from wind waves far exceeds the power produced by boat waves, which is due to the duration of the waves.  Boats usually only operate during the daytime and there is a limited number of boats that can fit comfortably on Ada Lake, especially when skiing or wakeboarding.  I estimated a total of 75 boat wakes per day, composed of 13 waves each.  However, with the wind assumed to blow all day long, it creates 86,400 waves per day, which results in a much greater daily wind power.

For wave power calculations and graphs, click here.

Sediment Resuspension:

While time duration is an important factor in wave power, it is not important in calculating sediment resuspension capabilities because the bottom velocity equation greatly depends on wave height.  The bottom velocity due to wind is less than the bottom velocity due to boats at low velocities, but greater than the bottom velocity due to boats at high velocities.  This is due to the fact that boat waves decrease with speed and wind waves increase with speed.  However, the average wind speed in the Ada Lake area is only 4.37 m/s.  So with the exception of storm events, boat waves will have more impact on bottom velocity than wind waves.

For sediment resuspension calculations and graph, click here.

Causes for Error:

There are many potential sources for error in this project. 

• I only used three different types of boats in my analysis, and different boats will produce different size waves.  However, I chose boats that will likely be common to Ada Lake if the lake is opened up to motorboats.  Also, I analyzed the MasterCraft X-Star, a wakeboarding boat that produces a larger wake than the vast majority of recreational boats.

• I assumed the wind direction to be from the southwest, making the fetch of the lake 685.5 m.  This is not always true since the wind changes direction, but it is a good assumption because it represents the largest fetch possible on the lake.

• I estimated the number of boats per day (5) and the number of passes per boat (15) on a typical day.  I feel that these are reasonable assumptions, but the number of boats and number of passes will vary from day to day. 

• I assumed the wind to be blowing for 24 hours a day.  This is obviously not always the case as wind speed will vary daily. 

• I analyzed sediment resuspension by calculating the bottom velocity produced by the waves.  While I believe the velocity calculations are correct, they do not directly correspond to sediment resuspension due to factors such as particle size and cohesion.

• Turbulence can also play a role in sediment resuspension and would be worth considering if I had more time.

On a final note, this project is not meant to be an all-encompassing, study to end all studies on boat-generated waves.  I made several assumptions and used fairly simple equations in my analysis.  However, I hope that I have shown trends in the significance of boat waves compared to wind waves on wave height, wave power, and bottom velocity for Ada Lake.  

Thanks for visiting.  If you have questions, email me at scallen@wisc.edu.