IV. Retreating Shorelines .....
219
Marshes appear to prevent erosion of the upland shoreline because the array of
stems substantially reduces wave height as a wave passes through a fringing
marsh and the plants eventually establish a dense mat of roots and partially
decayed plant material, marshes appear to provide reasonable erosion protection
for upland banks but in higher wave climates evolve to be erosion sensitive
themselves.
Protected with a reliable, low cost structure, the combination of marsh grasses
and breakwater should provide upland erosion protection for a wide range of
wave exposures and for a long functional life.
An experiment near Duck N.C. using a combination of a small wooden
breakwater and planting marsh grasses showed substantial potential for
controlling shoreline erosion. In a time of rising sea level and concern over
shrinking marshes, the combination of low breakwater and planted marsh
appears to offer substantial increases over the reliability of the marsh planting
zone and still cut the cost of shoreline protection by half of that bulkhead. Along
with unprotected marsh planting, the breakwater appears to be one of the few
erosion control options which is a clear environmental asset.
2.1.8
Tetrapods and Similar
Quarried rock is not readily available at all sites and its transport being onerous,
lumps of "false rocks" have been used. In Japan 50-ton concrete tetrapods have
been used to protect the east coast ofHonshu. Tetrapod barriers have been built at
Silt (Fed. Rep. Germany). Similar are tribars, tripods, dolosses and hanbars TM.
The hexagonally shaped Australian seabee, a rather recent development, can be
manufactured from a variety of materials, among others concrete and vitrified
clay. They can be used to build sea-walls or breakwaters. The honey-combed
structure was selected for projects near Sydney (CronuUa Beach) and Papua New
Guinea (Wewak Causeway in the northwest).
Tetrapods, a double layer even, have been used to armor a breakwater at Rota in
the Bay of Cadiz (Spain), more than 1000 of them, each weighing 25 metric tons
(27.6 US t). The toe of the structure is protected by concrete blocks of 250 m.t.
Nevertheless considerable destruction took place during the 1958 major storm.
Burger and his collaborators made full scale tests on tetrapods' resistance (W.W.
Burger, H. Oumeraci and H.W. Partensky, 1990, Stresses in tetrapods : results of
large scale model tests :Abstr. 221.C.C.E. (Delft, The Netherlands) 513-514).
219
Marshes appear to prevent erosion of the upland shoreline because the array of
stems substantially reduces wave height as a wave passes through a fringing
marsh and the plants eventually establish a dense mat of roots and partially
decayed plant material, marshes appear to provide reasonable erosion protection
for upland banks but in higher wave climates evolve to be erosion sensitive
themselves.
Protected with a reliable, low cost structure, the combination of marsh grasses
and breakwater should provide upland erosion protection for a wide range of
wave exposures and for a long functional life.
An experiment near Duck N.C. using a combination of a small wooden
breakwater and planting marsh grasses showed substantial potential for
controlling shoreline erosion. In a time of rising sea level and concern over
shrinking marshes, the combination of low breakwater and planted marsh
appears to offer substantial increases over the reliability of the marsh planting
zone and still cut the cost of shoreline protection by half of that bulkhead. Along
with unprotected marsh planting, the breakwater appears to be one of the few
erosion control options which is a clear environmental asset.
2.1.8
Tetrapods and Similar
Quarried rock is not readily available at all sites and its transport being onerous,
lumps of "false rocks" have been used. In Japan 50-ton concrete tetrapods have
been used to protect the east coast ofHonshu. Tetrapod barriers have been built at
Silt (Fed. Rep. Germany). Similar are tribars, tripods, dolosses and hanbars TM.
The hexagonally shaped Australian seabee, a rather recent development, can be
manufactured from a variety of materials, among others concrete and vitrified
clay. They can be used to build sea-walls or breakwaters. The honey-combed
structure was selected for projects near Sydney (CronuUa Beach) and Papua New
Guinea (Wewak Causeway in the northwest).
Tetrapods, a double layer even, have been used to armor a breakwater at Rota in
the Bay of Cadiz (Spain), more than 1000 of them, each weighing 25 metric tons
(27.6 US t). The toe of the structure is protected by concrete blocks of 250 m.t.
Nevertheless considerable destruction took place during the 1958 major storm.
Burger and his collaborators made full scale tests on tetrapods' resistance (W.W.
Burger, H. Oumeraci and H.W. Partensky, 1990, Stresses in tetrapods : results of
large scale model tests :Abstr. 221.C.C.E. (Delft, The Netherlands) 513-514).