Abstract: Systems for reinforcing various waterfront properties such as riverbanks, lake shores and beaches of oceans, bays and the like to protect them from erosion and encourage accretion of beach sand and gravel are disclosed. Improved seawalls and the like can be built from L-shaped members having a vertical wall portion, a horizontal footer, a vertical key protruding below the footer and an angular splash plate protruding from the wall opposite the footer. Systems based upon such seawalls may further comprise groins perpendicular thereto which are built from inverted "T"-shaped members, and optionally rows of such inverted "T" members parallel to the seawall as well. Further, erosion of the bank above the seawall and/or the beach below same may be reduced by partially covering them with water-permeable concrete mats. One or more groins extending perpendicular from the seawall may preferably be fabricated of inverted "Double T" members and adapted to support a pier.