Regions 3, 4, and 5) has been to build 

 bulkheads along vegetated shorelines 

 and then to backfill the area to create 

 wat::front real estate (Lindall 1973). 

 The natural shoreline is usually altered 

 by channelization, bulk heading, and fill- 

 ing. Houses are built on narrow strips 

 of land which are separated by a series 

 of dead-end channels (hence the name 

 "finger-type" development). The biolog- 

 ical effects of this type of development 

 in bays and estuaries have not been 

 well researched. However, several stud- 

 ies do give some indications of potential 

 impacts. Physical changes in estuaries 

 and bays include: reduction in acreage 

 of shore and marsh vegetation, changes 

 in marsh water circulation patterns and 

 nutrient input into the bay or estuary, 

 changes in water depth and substrates, 

 and the conversion of aquatic areas to 

 upland areas with a resulting decrease 

 in water area in the bay or estuary 

 (Corliss and Trent 1971, Cronin et al. 

 1971). 



The ecology of one finger-type 

 housing development in West Bay, 

 Texas, has been studied extensively. 

 Phytoplankton production (Corliss and 

 Trent 1971, Trent et al. 1976), sub- 

 strates, and hydrology (Trent et al. 

 1976)were studied in an open bay area, 

 in a bulkheaded canal area in the de- 

 velopment, and in an adjacent natural 

 marsh area. In general, productivity 

 was higher in the marsh than in canal 

 areas and lowest in the open bay. The 

 plankton blooms followed by low levels 

 of dissolved oxygen, high nutrient lev- 

 els, fish kills, and lowered production 

 of oysters, benthic macroin vertebrates, 

 and shrimp in summer months indicated 

 the presence of eutrophic conditions in 

 the canal areas of the housing develop- 

 ment. Similar eutrophic conditions have 

 been reported in housing developments 

 in Florida (Lindall 1973, Taylor and 

 Saloman 1968). Trent et al. (1972) 

 noted that standing crops of benthos, 

 fish, and crustaceans were relatively 

 high in the canal areas in spite of ap- 

 parent eutrophic conditions. The au- 

 thors were unsure if this was due to 

 canal areas in the housing development 

 being self-supporting in terms of vege- 

 tative production or whether productiv- 

 ity relied upon the detritus carried in 

 from the adjacent marsh by tidal action. 



REVETMENTS 



Definition 



A revetment is a sloped structure 

 built to protect existing land or newly 

 created embankments against erosion by 

 wave action, currents, or weather. Re- 

 vetments are usually placed parallel to 

 the natural shoreline. Riprap (randomly 

 placed stones) and gabions (a wicker- 

 like basket which can be filled with 

 stones) can be included in this defini- 

 tion. 



Structure Functions 



The primary function of most revet- 

 ments is to protect the area landward of 

 the revetment from erosion or scour due 

 to waves or currents. This protection 

 is due to the armoring characteristics 

 of the revetment and its ability to dis- 

 sipate wave energy. Revetments are nor- 

 mally used where it is necessary to re- 

 tain the shore in a more seaward posi- 

 tion relative to adjacent lands, where 

 there is little or no protective beach 

 in front of the land to be protected, or 

 where it is desired to maintain a cer- 

 tain depth of water in front of a struc- 

 ture. Revetments are especially useful 

 at the mouths of waterways where erosion 

 is frequently severe (Coastal Environ- 

 ments, Inc. 1976). They may also prevent 

 undermining from wave erosion when plac- 

 ed along the seaward slope of eroding 

 dunes or cliffs (Yasso and Hartman 

 1975). Revetments are often used to pro- 

 tect the foundations of structures, such 

 as bulkheads or buildings (Figure 29), 

 from erosion. Figures 30 and 31 give 

 examples of riprap and concrete revet- 

 ments. Revetments are generally used 

 where there is the potential for high 

 wave energy. Bulkheads can function in 

 a similar capacity, but offer far less 

 energy dissipation. 



Site Characteristics 



Revetments are generally built to 

 protect eroding shorelines. They are 

 found in many types of coastal habitats 

 including areas with eroding embankments 

 or cliffs and little or no protective 

 beach. Their most common occurrence is 

 in developed areas where the shorefront 

 property is endangered by erosion. 



58 



