Diving animals and tidal turbines

Tidal energy devices are becoming commonplace, particularly in Northern Europe, where several devices have been tested, or are already active. There is a huge potential in this predictable energy source, helping to guide us out of the fossil fuel era. However, high energy tidal environments are also home to a plethora of diving marine animals like seals, dolphins and seabirds. Assessing the risk of collision by particular species' is part of most environmental impact assessments, and is vitally important towards management of our ocean resources; living and otherwise.

Assessment of collision risk is a complicated process and there are many factors to take into account. For a full summary of factors view Page 16, Table 2 of the Scottish Natural Heritage guidance note.

This is just a short list of a few factors (click on the item to learn more):

There are many different types of tidal turbines, and some may or may not overlap with certain species.

Figure 5.2 from Robbins (2017) showing overlapping dive depths of birds and some tidal turbines

A sample collision risk model

There are several collision risk models that are used to assess the probability of an animal being struck by a device blade. An early implementation that is still used due to it's overall simplicity is the Encounter Rate Model (ERM) by Wilson et al. (2007). The formula for the ERM is defined as this:

D   x   Bb(w + 2r)(R + r)   x   v(1+(u2/3v2))

D = the ‘prey animal’ density, per m3
B = number of rotors (devices)
b = number of blades
w = the width of a turbine blade, as viewed from the side
R = the length of a turbine blade
r = the ‘effective radius’ – the clearance required due to the body size of the prey animal
v = the blade speed relative to the water, combining tangential speed and current speed
u = the prey animal’s swim speed relative to the water

Try for yourself!

We have populated all the fields here (except D) for you using data from the SNH Guidance note: (Page 83: Gannet)

See HERE for how we calculated D using data from Penguiness

Your collision risk estimate is: