The dissipation of energy and relative calm water created by the breakwaters can encourage deposition of sediments. (+)

 

However this can lead to excessive build up, leading to tombolo formation reducing longshore drift on the shore. (-)

 

This trapping of sediment can cause adverse effects down drift of the breakwaters leading to beach sediment starvation and increased erosion. (-)

 

It's very expensive to construct. (-)