A-Jacks are a commercially made concrete product used in both open channel and coastal applications. They consist of three long cement stakes joined at the middle, forming six legs. (External Link) They can be manufactured in sizes from 35 kg to 10 tonnes and more. Open channel applications include bank stabilization, flow and grade control, scour protection for bridge piers, and biostabilization. In coastal applications A-Jacks are used as breakwaters, revetments, artificial reefs, and habitat… (More on A-jack)