Jetties are built on both sides of a river or waterway for two primary reasons: to protect the channel from erosion and to keep the channel clear for navigation.
Erosion is a major problem for rivers and waterways. Over time, currents can gradually erode away at the banks and bottom of the channel. This can cause the channel to become shallower, narrower, and more difficult to navigate. Jetties help to prevent this by providing a physical barrier that protects the banks from the force of the current.
In addition, jetties help to keep the channel clear for navigation purposes. Debris and sediment can build up in a waterway over time, making it difficult or even impossible for boats and other vessels to pass through. By building jetties on both sides of the channel, this debris is prevented from accumulating in the middle, ensuring that thechannel remains clear and navigable.