Long series of groynes are built from both river sides to narrow river channels and prevent bank erosion with the aim to improve the conditions for inland navigation and prevent lateral channel migration. Single groynes or short series of groynes are built to impede local bank erosion. deviate the water flow. free an intake or fix the position of migrating bars at certain locations. https://www.ealisboa.com/best-flash-Nightstick-TWM-850XL-Tactical-Weapon-Mounted-Light-limited-super/