Rootwads are composed of the root mass or root ball of a large tree plus a portion of the trunk. They are used to armor a streambank by deflecting stream flows away from the bank. They also provide structural support for the streambank. By dissipating water velocities and erosive stresses along the bank, they protect the channel until dense riparian vegetation becomes established. Each revetment (the word revetment just means a barrier or retaining wall) will also generally have two to four mature willow transplants stuck into the root masses where the structure meets the streambank to speed revetation. Other plantings will help to improve the long-term stability of the bank.