The beauty is that the HEB works in pretty much any type of river, regardless of depth or flow speed (though that will have an impact on the quantity of power generated).
The barrel is one-piece moulded plastic with paddle treads and two integral planet gear driven permanent magnet generators installed making this a relatively light assembly for transportation and installation.
The rotating barrel turns the generator case which drives the planet gears which in turn spin the discs which holds the permanent magnets.
The movement of the magnets induces electrical current in the coils which are held stationary.
A more detailed description of the system can be seen on the HEB website at: https://www.hydro-electric-barrel.com/html/how_it_works.html