Willow spilling is a traditional form of riverbank stabilisation or revetment. Carried out during winter or early spring, live willow rods are woven around upright willow posts driven into the stream bank where erosion and collapse is occurring. In spring, these living willow rods and posts send out shoots and roots into the bank holding the soil firm, thus solving the problem.
This method is a soft form of river engineering, requiring minimal heavy equipment and so causing least disturbance to the river environment. A rough-finished surface to the wall of spilling is preferable. Such a surface slows the river flow near the bank allowing the slow moving water to deposit the silt and mud it carries, thus adding to the protection of the riverbank. Overtime, the increased deposits and the spreading willow roots stabilise the bank and create a naturalised wildlife habitat.