The wavebox creates a wave with no direction, just like a wave flow at a large lake or the sea, you kick up some sand, it washes back and forth and settles roughly where it was kicked up. In the ocean there are also direction currents, they clearly move in one direction, usually these are driven by thermalclines and tides. The 6100 would be used to simulate this form of current, working in tandem the wavebox will lift and suspend debris, the pump will then sweep it away.