Feb 11, 2019 · Although it is the oldest material used for this type of construction, wood is not good for seawall construction, but has many applications in retaining walls and marine barriers. In freshwater retaining walls, or walls that are built above the water line, wood is an affordable and popular option.. May 04, 2022 · The seawall size will help you select the suitable material because a giant seawall must be able to withstand the excessive soil and water force. That also includes how deep a seawall should be . Remember that some materials, like vinyl, are only strong enough and suitable for small seawalls..